Update module to 1.17 and update all deps

23 files changed, 4234 insertions, 0 deletions

diff --git a/vendor/golang.org/x/tools/internal/event/core/event.go b/vendor/golang.org/x/tools/internal/event/core/event.go
new file mode 100644
index 0000000..a6cf0e6
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/event/core/event.go
@@ -0,0 +1,85 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package core provides support for event based telemetry.
+package core
+
+import (
+	"fmt"
+	"time"
+
+	"golang.org/x/tools/internal/event/label"
+)
+
+// Event holds the information about an event of note that occurred.
+type Event struct {
+	at time.Time
+
+	// As events are often on the stack, storing the first few labels directly
+	// in the event can avoid an allocation at all for the very common cases of
+	// simple events.
+	// The length needs to be large enough to cope with the majority of events
+	// but no so large as to cause undue stack pressure.
+	// A log message with two values will use 3 labels (one for each value and
+	// one for the message itself).
+
+	static  [3]label.Label // inline storage for the first few labels
+	dynamic []label.Label  // dynamically sized storage for remaining labels
+}
+
+// eventLabelMap implements label.Map for a the labels of an Event.
+type eventLabelMap struct {
+	event Event
+}
+
+func (ev Event) At() time.Time { return ev.at }
+
+func (ev Event) Format(f fmt.State, r rune) {
+	if !ev.at.IsZero() {
+		fmt.Fprint(f, ev.at.Format("2006/01/02 15:04:05 "))
+	}
+	for index := 0; ev.Valid(index); index++ {
+		if l := ev.Label(index); l.Valid() {
+			fmt.Fprintf(f, "\n\t%v", l)
+		}
+	}
+}
+
+func (ev Event) Valid(index int) bool {
+	return index >= 0 && index < len(ev.static)+len(ev.dynamic)
+}
+
+func (ev Event) Label(index int) label.Label {
+	if index < len(ev.static) {
+		return ev.static[index]
+	}
+	return ev.dynamic[index-len(ev.static)]
+}
+
+func (ev Event) Find(key label.Key) label.Label {
+	for _, l := range ev.static {
+		if l.Key() == key {
+			return l
+		}
+	}
+	for _, l := range ev.dynamic {
+		if l.Key() == key {
+			return l
+		}
+	}
+	return label.Label{}
+}
+
+func MakeEvent(static [3]label.Label, labels []label.Label) Event {
+	return Event{
+		static:  static,
+		dynamic: labels,
+	}
+}
+
+// CloneEvent event returns a copy of the event with the time adjusted to at.
+func CloneEvent(ev Event, at time.Time) Event {
+	ev.at = at
+	return ev
+}
diff --git a/vendor/golang.org/x/tools/internal/event/core/export.go b/vendor/golang.org/x/tools/internal/event/core/export.go
new file mode 100644
index 0000000..05f3a9a
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/event/core/export.go
@@ -0,0 +1,70 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package core
+
+import (
+	"context"
+	"sync/atomic"
+	"time"
+	"unsafe"
+
+	"golang.org/x/tools/internal/event/label"
+)
+
+// Exporter is a function that handles events.
+// It may return a modified context and event.
+type Exporter func(context.Context, Event, label.Map) context.Context
+
+var (
+	exporter unsafe.Pointer
+)
+
+// SetExporter sets the global exporter function that handles all events.
+// The exporter is called synchronously from the event call site, so it should
+// return quickly so as not to hold up user code.
+func SetExporter(e Exporter) {
+	p := unsafe.Pointer(&e)
+	if e == nil {
+		// &e is always valid, and so p is always valid, but for the early abort
+		// of ProcessEvent to be efficient it needs to make the nil check on the
+		// pointer without having to dereference it, so we make the nil function
+		// also a nil pointer
+		p = nil
+	}
+	atomic.StorePointer(&exporter, p)
+}
+
+// deliver is called to deliver an event to the supplied exporter.
+// it will fill in the time.
+func deliver(ctx context.Context, exporter Exporter, ev Event) context.Context {
+	// add the current time to the event
+	ev.at = time.Now()
+	// hand the event off to the current exporter
+	return exporter(ctx, ev, ev)
+}
+
+// Export is called to deliver an event to the global exporter if set.
+func Export(ctx context.Context, ev Event) context.Context {
+	// get the global exporter and abort early if there is not one
+	exporterPtr := (*Exporter)(atomic.LoadPointer(&exporter))
+	if exporterPtr == nil {
+		return ctx
+	}
+	return deliver(ctx, *exporterPtr, ev)
+}
+
+// ExportPair is called to deliver a start event to the supplied exporter.
+// It also returns a function that will deliver the end event to the same
+// exporter.
+// It will fill in the time.
+func ExportPair(ctx context.Context, begin, end Event) (context.Context, func()) {
+	// get the global exporter and abort early if there is not one
+	exporterPtr := (*Exporter)(atomic.LoadPointer(&exporter))
+	if exporterPtr == nil {
+		return ctx, func() {}
+	}
+	ctx = deliver(ctx, *exporterPtr, begin)
+	return ctx, func() { deliver(ctx, *exporterPtr, end) }
+}
diff --git a/vendor/golang.org/x/tools/internal/event/core/fast.go b/vendor/golang.org/x/tools/internal/event/core/fast.go
new file mode 100644
index 0000000..06c1d46
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/event/core/fast.go
@@ -0,0 +1,77 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package core
+
+import (
+	"context"
+
+	"golang.org/x/tools/internal/event/keys"
+	"golang.org/x/tools/internal/event/label"
+)
+
+// Log1 takes a message and one label delivers a log event to the exporter.
+// It is a customized version of Print that is faster and does no allocation.
+func Log1(ctx context.Context, message string, t1 label.Label) {
+	Export(ctx, MakeEvent([3]label.Label{
+		keys.Msg.Of(message),
+		t1,
+	}, nil))
+}
+
+// Log2 takes a message and two labels and delivers a log event to the exporter.
+// It is a customized version of Print that is faster and does no allocation.
+func Log2(ctx context.Context, message string, t1 label.Label, t2 label.Label) {
+	Export(ctx, MakeEvent([3]label.Label{
+		keys.Msg.Of(message),
+		t1,
+		t2,
+	}, nil))
+}
+
+// Metric1 sends a label event to the exporter with the supplied labels.
+func Metric1(ctx context.Context, t1 label.Label) context.Context {
+	return Export(ctx, MakeEvent([3]label.Label{
+		keys.Metric.New(),
+		t1,
+	}, nil))
+}
+
+// Metric2 sends a label event to the exporter with the supplied labels.
+func Metric2(ctx context.Context, t1, t2 label.Label) context.Context {
+	return Export(ctx, MakeEvent([3]label.Label{
+		keys.Metric.New(),
+		t1,
+		t2,
+	}, nil))
+}
+
+// Start1 sends a span start event with the supplied label list to the exporter.
+// It also returns a function that will end the span, which should normally be
+// deferred.
+func Start1(ctx context.Context, name string, t1 label.Label) (context.Context, func()) {
+	return ExportPair(ctx,
+		MakeEvent([3]label.Label{
+			keys.Start.Of(name),
+			t1,
+		}, nil),
+		MakeEvent([3]label.Label{
+			keys.End.New(),
+		}, nil))
+}
+
+// Start2 sends a span start event with the supplied label list to the exporter.
+// It also returns a function that will end the span, which should normally be
+// deferred.
+func Start2(ctx context.Context, name string, t1, t2 label.Label) (context.Context, func()) {
+	return ExportPair(ctx,
+		MakeEvent([3]label.Label{
+			keys.Start.Of(name),
+			t1,
+			t2,
+		}, nil),
+		MakeEvent([3]label.Label{
+			keys.End.New(),
+		}, nil))
+}
diff --git a/vendor/golang.org/x/tools/internal/event/doc.go b/vendor/golang.org/x/tools/internal/event/doc.go
new file mode 100644
index 0000000..5dc6e6b
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/event/doc.go
@@ -0,0 +1,7 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package event provides a set of packages that cover the main
+// concepts of telemetry in an implementation agnostic way.
+package event
diff --git a/vendor/golang.org/x/tools/internal/event/event.go b/vendor/golang.org/x/tools/internal/event/event.go
new file mode 100644
index 0000000..4d55e57
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/event/event.go
@@ -0,0 +1,127 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package event
+
+import (
+	"context"
+
+	"golang.org/x/tools/internal/event/core"
+	"golang.org/x/tools/internal/event/keys"
+	"golang.org/x/tools/internal/event/label"
+)
+
+// Exporter is a function that handles events.
+// It may return a modified context and event.
+type Exporter func(context.Context, core.Event, label.Map) context.Context
+
+// SetExporter sets the global exporter function that handles all events.
+// The exporter is called synchronously from the event call site, so it should
+// return quickly so as not to hold up user code.
+func SetExporter(e Exporter) {
+	core.SetExporter(core.Exporter(e))
+}
+
+// Log takes a message and a label list and combines them into a single event
+// before delivering them to the exporter.
+func Log(ctx context.Context, message string, labels ...label.Label) {
+	core.Export(ctx, core.MakeEvent([3]label.Label{
+		keys.Msg.Of(message),
+	}, labels))
+}
+
+// IsLog returns true if the event was built by the Log function.
+// It is intended to be used in exporters to identify the semantics of the
+// event when deciding what to do with it.
+func IsLog(ev core.Event) bool {
+	return ev.Label(0).Key() == keys.Msg
+}
+
+// Error takes a message and a label list and combines them into a single event
+// before delivering them to the exporter. It captures the error in the
+// delivered event.
+func Error(ctx context.Context, message string, err error, labels ...label.Label) {
+	core.Export(ctx, core.MakeEvent([3]label.Label{
+		keys.Msg.Of(message),
+		keys.Err.Of(err),
+	}, labels))
+}
+
+// IsError returns true if the event was built by the Error function.
+// It is intended to be used in exporters to identify the semantics of the
+// event when deciding what to do with it.
+func IsError(ev core.Event) bool {
+	return ev.Label(0).Key() == keys.Msg &&
+		ev.Label(1).Key() == keys.Err
+}
+
+// Metric sends a label event to the exporter with the supplied labels.
+func Metric(ctx context.Context, labels ...label.Label) {
+	core.Export(ctx, core.MakeEvent([3]label.Label{
+		keys.Metric.New(),
+	}, labels))
+}
+
+// IsMetric returns true if the event was built by the Metric function.
+// It is intended to be used in exporters to identify the semantics of the
+// event when deciding what to do with it.
+func IsMetric(ev core.Event) bool {
+	return ev.Label(0).Key() == keys.Metric
+}
+
+// Label sends a label event to the exporter with the supplied labels.
+func Label(ctx context.Context, labels ...label.Label) context.Context {
+	return core.Export(ctx, core.MakeEvent([3]label.Label{
+		keys.Label.New(),
+	}, labels))
+}
+
+// IsLabel returns true if the event was built by the Label function.
+// It is intended to be used in exporters to identify the semantics of the
+// event when deciding what to do with it.
+func IsLabel(ev core.Event) bool {
+	return ev.Label(0).Key() == keys.Label
+}
+
+// Start sends a span start event with the supplied label list to the exporter.
+// It also returns a function that will end the span, which should normally be
+// deferred.
+func Start(ctx context.Context, name string, labels ...label.Label) (context.Context, func()) {
+	return core.ExportPair(ctx,
+		core.MakeEvent([3]label.Label{
+			keys.Start.Of(name),
+		}, labels),
+		core.MakeEvent([3]label.Label{
+			keys.End.New(),
+		}, nil))
+}
+
+// IsStart returns true if the event was built by the Start function.
+// It is intended to be used in exporters to identify the semantics of the
+// event when deciding what to do with it.
+func IsStart(ev core.Event) bool {
+	return ev.Label(0).Key() == keys.Start
+}
+
+// IsEnd returns true if the event was built by the End function.
+// It is intended to be used in exporters to identify the semantics of the
+// event when deciding what to do with it.
+func IsEnd(ev core.Event) bool {
+	return ev.Label(0).Key() == keys.End
+}
+
+// Detach returns a context without an associated span.
+// This allows the creation of spans that are not children of the current span.
+func Detach(ctx context.Context) context.Context {
+	return core.Export(ctx, core.MakeEvent([3]label.Label{
+		keys.Detach.New(),
+	}, nil))
+}
+
+// IsDetach returns true if the event was built by the Detach function.
+// It is intended to be used in exporters to identify the semantics of the
+// event when deciding what to do with it.
+func IsDetach(ev core.Event) bool {
+	return ev.Label(0).Key() == keys.Detach
+}
diff --git a/vendor/golang.org/x/tools/internal/event/keys/keys.go b/vendor/golang.org/x/tools/internal/event/keys/keys.go
new file mode 100644
index 0000000..a02206e
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/event/keys/keys.go
@@ -0,0 +1,564 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package keys
+
+import (
+	"fmt"
+	"io"
+	"math"
+	"strconv"
+
+	"golang.org/x/tools/internal/event/label"
+)
+
+// Value represents a key for untyped values.
+type Value struct {
+	name        string
+	description string
+}
+
+// New creates a new Key for untyped values.
+func New(name, description string) *Value {
+	return &Value{name: name, description: description}
+}
+
+func (k *Value) Name() string        { return k.name }
+func (k *Value) Description() string { return k.description }
+
+func (k *Value) Format(w io.Writer, buf []byte, l label.Label) {
+	fmt.Fprint(w, k.From(l))
+}
+
+// Get can be used to get a label for the key from a label.Map.
+func (k *Value) Get(lm label.Map) interface{} {
+	if t := lm.Find(k); t.Valid() {
+		return k.From(t)
+	}
+	return nil
+}
+
+// From can be used to get a value from a Label.
+func (k *Value) From(t label.Label) interface{} { return t.UnpackValue() }
+
+// Of creates a new Label with this key and the supplied value.
+func (k *Value) Of(value interface{}) label.Label { return label.OfValue(k, value) }
+
+// Tag represents a key for tagging labels that have no value.
+// These are used when the existence of the label is the entire information it
+// carries, such as marking events to be of a specific kind, or from a specific
+// package.
+type Tag struct {
+	name        string
+	description string
+}
+
+// NewTag creates a new Key for tagging labels.
+func NewTag(name, description string) *Tag {
+	return &Tag{name: name, description: description}
+}
+
+func (k *Tag) Name() string        { return k.name }
+func (k *Tag) Description() string { return k.description }
+
+func (k *Tag) Format(w io.Writer, buf []byte, l label.Label) {}
+
+// New creates a new Label with this key.
+func (k *Tag) New() label.Label { return label.OfValue(k, nil) }
+
+// Int represents a key
+type Int struct {
+	name        string
+	description string
+}
+
+// NewInt creates a new Key for int values.
+func NewInt(name, description string) *Int {
+	return &Int{name: name, description: description}
+}
+
+func (k *Int) Name() string        { return k.name }
+func (k *Int) Description() string { return k.description }
+
+func (k *Int) Format(w io.Writer, buf []byte, l label.Label) {
+	w.Write(strconv.AppendInt(buf, int64(k.From(l)), 10))
+}
+
+// Of creates a new Label with this key and the supplied value.
+func (k *Int) Of(v int) label.Label { return label.Of64(k, uint64(v)) }
+
+// Get can be used to get a label for the key from a label.Map.
+func (k *Int) Get(lm label.Map) int {
+	if t := lm.Find(k); t.Valid() {
+		return k.From(t)
+	}
+	return 0
+}
+
+// From can be used to get a value from a Label.
+func (k *Int) From(t label.Label) int { return int(t.Unpack64()) }
+
+// Int8 represents a key
+type Int8 struct {
+	name        string
+	description string
+}
+
+// NewInt8 creates a new Key for int8 values.
+func NewInt8(name, description string) *Int8 {
+	return &Int8{name: name, description: description}
+}
+
+func (k *Int8) Name() string        { return k.name }
+func (k *Int8) Description() string { return k.description }
+
+func (k *Int8) Format(w io.Writer, buf []byte, l label.Label) {
+	w.Write(strconv.AppendInt(buf, int64(k.From(l)), 10))
+}
+
+// Of creates a new Label with this key and the supplied value.
+func (k *Int8) Of(v int8) label.Label { return label.Of64(k, uint64(v)) }
+
+// Get can be used to get a label for the key from a label.Map.
+func (k *Int8) Get(lm label.Map) int8 {
+	if t := lm.Find(k); t.Valid() {
+		return k.From(t)
+	}
+	return 0
+}
+
+// From can be used to get a value from a Label.
+func (k *Int8) From(t label.Label) int8 { return int8(t.Unpack64()) }
+
+// Int16 represents a key
+type Int16 struct {
+	name        string
+	description string
+}
+
+// NewInt16 creates a new Key for int16 values.
+func NewInt16(name, description string) *Int16 {
+	return &Int16{name: name, description: description}
+}
+
+func (k *Int16) Name() string        { return k.name }
+func (k *Int16) Description() string { return k.description }
+
+func (k *Int16) Format(w io.Writer, buf []byte, l label.Label) {
+	w.Write(strconv.AppendInt(buf, int64(k.From(l)), 10))
+}
+
+// Of creates a new Label with this key and the supplied value.
+func (k *Int16) Of(v int16) label.Label { return label.Of64(k, uint64(v)) }
+
+// Get can be used to get a label for the key from a label.Map.
+func (k *Int16) Get(lm label.Map) int16 {
+	if t := lm.Find(k); t.Valid() {
+		return k.From(t)
+	}
+	return 0
+}
+
+// From can be used to get a value from a Label.
+func (k *Int16) From(t label.Label) int16 { return int16(t.Unpack64()) }
+
+// Int32 represents a key
+type Int32 struct {
+	name        string
+	description string
+}
+
+// NewInt32 creates a new Key for int32 values.
+func NewInt32(name, description string) *Int32 {
+	return &Int32{name: name, description: description}
+}
+
+func (k *Int32) Name() string        { return k.name }
+func (k *Int32) Description() string { return k.description }
+
+func (k *Int32) Format(w io.Writer, buf []byte, l label.Label) {
+	w.Write(strconv.AppendInt(buf, int64(k.From(l)), 10))
+}
+
+// Of creates a new Label with this key and the supplied value.
+func (k *Int32) Of(v int32) label.Label { return label.Of64(k, uint64(v)) }
+
+// Get can be used to get a label for the key from a label.Map.
+func (k *Int32) Get(lm label.Map) int32 {
+	if t := lm.Find(k); t.Valid() {
+		return k.From(t)
+	}
+	return 0
+}
+
+// From can be used to get a value from a Label.
+func (k *Int32) From(t label.Label) int32 { return int32(t.Unpack64()) }
+
+// Int64 represents a key
+type Int64 struct {
+	name        string
+	description string
+}
+
+// NewInt64 creates a new Key for int64 values.
+func NewInt64(name, description string) *Int64 {
+	return &Int64{name: name, description: description}
+}
+
+func (k *Int64) Name() string        { return k.name }
+func (k *Int64) Description() string { return k.description }
+
+func (k *Int64) Format(w io.Writer, buf []byte, l label.Label) {
+	w.Write(strconv.AppendInt(buf, k.From(l), 10))
+}
+
+// Of creates a new Label with this key and the supplied value.
+func (k *Int64) Of(v int64) label.Label { return label.Of64(k, uint64(v)) }
+
+// Get can be used to get a label for the key from a label.Map.
+func (k *Int64) Get(lm label.Map) int64 {
+	if t := lm.Find(k); t.Valid() {
+		return k.From(t)
+	}
+	return 0
+}
+
+// From can be used to get a value from a Label.
+func (k *Int64) From(t label.Label) int64 { return int64(t.Unpack64()) }
+
+// UInt represents a key
+type UInt struct {
+	name        string
+	description string
+}
+
+// NewUInt creates a new Key for uint values.
+func NewUInt(name, description string) *UInt {
+	return &UInt{name: name, description: description}
+}
+
+func (k *UInt) Name() string        { return k.name }
+func (k *UInt) Description() string { return k.description }
+
+func (k *UInt) Format(w io.Writer, buf []byte, l label.Label) {
+	w.Write(strconv.AppendUint(buf, uint64(k.From(l)), 10))
+}
+
+// Of creates a new Label with this key and the supplied value.
+func (k *UInt) Of(v uint) label.Label { return label.Of64(k, uint64(v)) }
+
+// Get can be used to get a label for the key from a label.Map.
+func (k *UInt) Get(lm label.Map) uint {
+	if t := lm.Find(k); t.Valid() {
+		return k.From(t)
+	}
+	return 0
+}
+
+// From can be used to get a value from a Label.
+func (k *UInt) From(t label.Label) uint { return uint(t.Unpack64()) }
+
+// UInt8 represents a key
+type UInt8 struct {
+	name        string
+	description string
+}
+
+// NewUInt8 creates a new Key for uint8 values.
+func NewUInt8(name, description string) *UInt8 {
+	return &UInt8{name: name, description: description}
+}
+
+func (k *UInt8) Name() string        { return k.name }
+func (k *UInt8) Description() string { return k.description }
+
+func (k *UInt8) Format(w io.Writer, buf []byte, l label.Label) {
+	w.Write(strconv.AppendUint(buf, uint64(k.From(l)), 10))
+}
+
+// Of creates a new Label with this key and the supplied value.
+func (k *UInt8) Of(v uint8) label.Label { return label.Of64(k, uint64(v)) }
+
+// Get can be used to get a label for the key from a label.Map.
+func (k *UInt8) Get(lm label.Map) uint8 {
+	if t := lm.Find(k); t.Valid() {
+		return k.From(t)
+	}
+	return 0
+}
+
+// From can be used to get a value from a Label.
+func (k *UInt8) From(t label.Label) uint8 { return uint8(t.Unpack64()) }
+
+// UInt16 represents a key
+type UInt16 struct {
+	name        string
+	description string
+}
+
+// NewUInt16 creates a new Key for uint16 values.
+func NewUInt16(name, description string) *UInt16 {
+	return &UInt16{name: name, description: description}
+}
+
+func (k *UInt16) Name() string        { return k.name }
+func (k *UInt16) Description() string { return k.description }
+
+func (k *UInt16) Format(w io.Writer, buf []byte, l label.Label) {
+	w.Write(strconv.AppendUint(buf, uint64(k.From(l)), 10))
+}
+
+// Of creates a new Label with this key and the supplied value.
+func (k *UInt16) Of(v uint16) label.Label { return label.Of64(k, uint64(v)) }
+
+// Get can be used to get a label for the key from a label.Map.
+func (k *UInt16) Get(lm label.Map) uint16 {
+	if t := lm.Find(k); t.Valid() {
+		return k.From(t)
+	}
+	return 0
+}
+
+// From can be used to get a value from a Label.
+func (k *UInt16) From(t label.Label) uint16 { return uint16(t.Unpack64()) }
+
+// UInt32 represents a key
+type UInt32 struct {
+	name        string
+	description string
+}
+
+// NewUInt32 creates a new Key for uint32 values.
+func NewUInt32(name, description string) *UInt32 {
+	return &UInt32{name: name, description: description}
+}
+
+func (k *UInt32) Name() string        { return k.name }
+func (k *UInt32) Description() string { return k.description }
+
+func (k *UInt32) Format(w io.Writer, buf []byte, l label.Label) {
+	w.Write(strconv.AppendUint(buf, uint64(k.From(l)), 10))
+}
+
+// Of creates a new Label with this key and the supplied value.
+func (k *UInt32) Of(v uint32) label.Label { return label.Of64(k, uint64(v)) }
+
+// Get can be used to get a label for the key from a label.Map.
+func (k *UInt32) Get(lm label.Map) uint32 {
+	if t := lm.Find(k); t.Valid() {
+		return k.From(t)
+	}
+	return 0
+}
+
+// From can be used to get a value from a Label.
+func (k *UInt32) From(t label.Label) uint32 { return uint32(t.Unpack64()) }
+
+// UInt64 represents a key
+type UInt64 struct {
+	name        string
+	description string
+}
+
+// NewUInt64 creates a new Key for uint64 values.
+func NewUInt64(name, description string) *UInt64 {
+	return &UInt64{name: name, description: description}
+}
+
+func (k *UInt64) Name() string        { return k.name }
+func (k *UInt64) Description() string { return k.description }
+
+func (k *UInt64) Format(w io.Writer, buf []byte, l label.Label) {
+	w.Write(strconv.AppendUint(buf, k.From(l), 10))
+}
+
+// Of creates a new Label with this key and the supplied value.
+func (k *UInt64) Of(v uint64) label.Label { return label.Of64(k, v) }
+
+// Get can be used to get a label for the key from a label.Map.
+func (k *UInt64) Get(lm label.Map) uint64 {
+	if t := lm.Find(k); t.Valid() {
+		return k.From(t)
+	}
+	return 0
+}
+
+// From can be used to get a value from a Label.
+func (k *UInt64) From(t label.Label) uint64 { return t.Unpack64() }
+
+// Float32 represents a key
+type Float32 struct {
+	name        string
+	description string
+}
+
+// NewFloat32 creates a new Key for float32 values.
+func NewFloat32(name, description string) *Float32 {
+	return &Float32{name: name, description: description}
+}
+
+func (k *Float32) Name() string        { return k.name }
+func (k *Float32) Description() string { return k.description }
+
+func (k *Float32) Format(w io.Writer, buf []byte, l label.Label) {
+	w.Write(strconv.AppendFloat(buf, float64(k.From(l)), 'E', -1, 32))
+}
+
+// Of creates a new Label with this key and the supplied value.
+func (k *Float32) Of(v float32) label.Label {
+	return label.Of64(k, uint64(math.Float32bits(v)))
+}
+
+// Get can be used to get a label for the key from a label.Map.
+func (k *Float32) Get(lm label.Map) float32 {
+	if t := lm.Find(k); t.Valid() {
+		return k.From(t)
+	}
+	return 0
+}
+
+// From can be used to get a value from a Label.
+func (k *Float32) From(t label.Label) float32 {
+	return math.Float32frombits(uint32(t.Unpack64()))
+}
+
+// Float64 represents a key
+type Float64 struct {
+	name        string
+	description string
+}
+
+// NewFloat64 creates a new Key for int64 values.
+func NewFloat64(name, description string) *Float64 {
+	return &Float64{name: name, description: description}
+}
+
+func (k *Float64) Name() string        { return k.name }
+func (k *Float64) Description() string { return k.description }
+
+func (k *Float64) Format(w io.Writer, buf []byte, l label.Label) {
+	w.Write(strconv.AppendFloat(buf, k.From(l), 'E', -1, 64))
+}
+
+// Of creates a new Label with this key and the supplied value.
+func (k *Float64) Of(v float64) label.Label {
+	return label.Of64(k, math.Float64bits(v))
+}
+
+// Get can be used to get a label for the key from a label.Map.
+func (k *Float64) Get(lm label.Map) float64 {
+	if t := lm.Find(k); t.Valid() {
+		return k.From(t)
+	}
+	return 0
+}
+
+// From can be used to get a value from a Label.
+func (k *Float64) From(t label.Label) float64 {
+	return math.Float64frombits(t.Unpack64())
+}
+
+// String represents a key
+type String struct {
+	name        string
+	description string
+}
+
+// NewString creates a new Key for int64 values.
+func NewString(name, description string) *String {
+	return &String{name: name, description: description}
+}
+
+func (k *String) Name() string        { return k.name }
+func (k *String) Description() string { return k.description }
+
+func (k *String) Format(w io.Writer, buf []byte, l label.Label) {
+	w.Write(strconv.AppendQuote(buf, k.From(l)))
+}
+
+// Of creates a new Label with this key and the supplied value.
+func (k *String) Of(v string) label.Label { return label.OfString(k, v) }
+
+// Get can be used to get a label for the key from a label.Map.
+func (k *String) Get(lm label.Map) string {
+	if t := lm.Find(k); t.Valid() {
+		return k.From(t)
+	}
+	return ""
+}
+
+// From can be used to get a value from a Label.
+func (k *String) From(t label.Label) string { return t.UnpackString() }
+
+// Boolean represents a key
+type Boolean struct {
+	name        string
+	description string
+}
+
+// NewBoolean creates a new Key for bool values.
+func NewBoolean(name, description string) *Boolean {
+	return &Boolean{name: name, description: description}
+}
+
+func (k *Boolean) Name() string        { return k.name }
+func (k *Boolean) Description() string { return k.description }
+
+func (k *Boolean) Format(w io.Writer, buf []byte, l label.Label) {
+	w.Write(strconv.AppendBool(buf, k.From(l)))
+}
+
+// Of creates a new Label with this key and the supplied value.
+func (k *Boolean) Of(v bool) label.Label {
+	if v {
+		return label.Of64(k, 1)
+	}
+	return label.Of64(k, 0)
+}
+
+// Get can be used to get a label for the key from a label.Map.
+func (k *Boolean) Get(lm label.Map) bool {
+	if t := lm.Find(k); t.Valid() {
+		return k.From(t)
+	}
+	return false
+}
+
+// From can be used to get a value from a Label.
+func (k *Boolean) From(t label.Label) bool { return t.Unpack64() > 0 }
+
+// Error represents a key
+type Error struct {
+	name        string
+	description string
+}
+
+// NewError creates a new Key for int64 values.
+func NewError(name, description string) *Error {
+	return &Error{name: name, description: description}
+}
+
+func (k *Error) Name() string        { return k.name }
+func (k *Error) Description() string { return k.description }
+
+func (k *Error) Format(w io.Writer, buf []byte, l label.Label) {
+	io.WriteString(w, k.From(l).Error())
+}
+
+// Of creates a new Label with this key and the supplied value.
+func (k *Error) Of(v error) label.Label { return label.OfValue(k, v) }
+
+// Get can be used to get a label for the key from a label.Map.
+func (k *Error) Get(lm label.Map) error {
+	if t := lm.Find(k); t.Valid() {
+		return k.From(t)
+	}
+	return nil
+}
+
+// From can be used to get a value from a Label.
+func (k *Error) From(t label.Label) error {
+	err, _ := t.UnpackValue().(error)
+	return err
+}
diff --git a/vendor/golang.org/x/tools/internal/event/keys/standard.go b/vendor/golang.org/x/tools/internal/event/keys/standard.go
new file mode 100644
index 0000000..7e95866
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/event/keys/standard.go
@@ -0,0 +1,22 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package keys
+
+var (
+	// Msg is a key used to add message strings to label lists.
+	Msg = NewString("message", "a readable message")
+	// Label is a key used to indicate an event adds labels to the context.
+	Label = NewTag("label", "a label context marker")
+	// Start is used for things like traces that have a name.
+	Start = NewString("start", "span start")
+	// Metric is a key used to indicate an event records metrics.
+	End = NewTag("end", "a span end marker")
+	// Metric is a key used to indicate an event records metrics.
+	Detach = NewTag("detach", "a span detach marker")
+	// Err is a key used to add error values to label lists.
+	Err = NewError("error", "an error that occurred")
+	// Metric is a key used to indicate an event records metrics.
+	Metric = NewTag("metric", "a metric event marker")
+)
diff --git a/vendor/golang.org/x/tools/internal/event/label/label.go b/vendor/golang.org/x/tools/internal/event/label/label.go
new file mode 100644
index 0000000..0f526e1
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/event/label/label.go
@@ -0,0 +1,215 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package label
+
+import (
+	"fmt"
+	"io"
+	"reflect"
+	"unsafe"
+)
+
+// Key is used as the identity of a Label.
+// Keys are intended to be compared by pointer only, the name should be unique
+// for communicating with external systems, but it is not required or enforced.
+type Key interface {
+	// Name returns the key name.
+	Name() string
+	// Description returns a string that can be used to describe the value.
+	Description() string
+
+	// Format is used in formatting to append the value of the label to the
+	// supplied buffer.
+	// The formatter may use the supplied buf as a scratch area to avoid
+	// allocations.
+	Format(w io.Writer, buf []byte, l Label)
+}
+
+// Label holds a key and value pair.
+// It is normally used when passing around lists of labels.
+type Label struct {
+	key     Key
+	packed  uint64
+	untyped interface{}
+}
+
+// Map is the interface to a collection of Labels indexed by key.
+type Map interface {
+	// Find returns the label that matches the supplied key.
+	Find(key Key) Label
+}
+
+// List is the interface to something that provides an iterable
+// list of labels.
+// Iteration should start from 0 and continue until Valid returns false.
+type List interface {
+	// Valid returns true if the index is within range for the list.
+	// It does not imply the label at that index will itself be valid.
+	Valid(index int) bool
+	// Label returns the label at the given index.
+	Label(index int) Label
+}
+
+// list implements LabelList for a list of Labels.
+type list struct {
+	labels []Label
+}
+
+// filter wraps a LabelList filtering out specific labels.
+type filter struct {
+	keys       []Key
+	underlying List
+}
+
+// listMap implements LabelMap for a simple list of labels.
+type listMap struct {
+	labels []Label
+}
+
+// mapChain implements LabelMap for a list of underlying LabelMap.
+type mapChain struct {
+	maps []Map
+}
+
+// OfValue creates a new label from the key and value.
+// This method is for implementing new key types, label creation should
+// normally be done with the Of method of the key.
+func OfValue(k Key, value interface{}) Label { return Label{key: k, untyped: value} }
+
+// UnpackValue assumes the label was built using LabelOfValue and returns the value
+// that was passed to that constructor.
+// This method is for implementing new key types, for type safety normal
+// access should be done with the From method of the key.
+func (t Label) UnpackValue() interface{} { return t.untyped }
+
+// Of64 creates a new label from a key and a uint64. This is often
+// used for non uint64 values that can be packed into a uint64.
+// This method is for implementing new key types, label creation should
+// normally be done with the Of method of the key.
+func Of64(k Key, v uint64) Label { return Label{key: k, packed: v} }
+
+// Unpack64 assumes the label was built using LabelOf64 and returns the value that
+// was passed to that constructor.
+// This method is for implementing new key types, for type safety normal
+// access should be done with the From method of the key.
+func (t Label) Unpack64() uint64 { return t.packed }
+
+type stringptr unsafe.Pointer
+
+// OfString creates a new label from a key and a string.
+// This method is for implementing new key types, label creation should
+// normally be done with the Of method of the key.
+func OfString(k Key, v string) Label {
+	hdr := (*reflect.StringHeader)(unsafe.Pointer(&v))
+	return Label{
+		key:     k,
+		packed:  uint64(hdr.Len),
+		untyped: stringptr(hdr.Data),
+	}
+}
+
+// UnpackString assumes the label was built using LabelOfString and returns the
+// value that was passed to that constructor.
+// This method is for implementing new key types, for type safety normal
+// access should be done with the From method of the key.
+func (t Label) UnpackString() string {
+	var v string
+	hdr := (*reflect.StringHeader)(unsafe.Pointer(&v))
+	hdr.Data = uintptr(t.untyped.(stringptr))
+	hdr.Len = int(t.packed)
+	return v
+}
+
+// Valid returns true if the Label is a valid one (it has a key).
+func (t Label) Valid() bool { return t.key != nil }
+
+// Key returns the key of this Label.
+func (t Label) Key() Key { return t.key }
+
+// Format is used for debug printing of labels.
+func (t Label) Format(f fmt.State, r rune) {
+	if !t.Valid() {
+		io.WriteString(f, `nil`)
+		return
+	}
+	io.WriteString(f, t.Key().Name())
+	io.WriteString(f, "=")
+	var buf [128]byte
+	t.Key().Format(f, buf[:0], t)
+}
+
+func (l *list) Valid(index int) bool {
+	return index >= 0 && index < len(l.labels)
+}
+
+func (l *list) Label(index int) Label {
+	return l.labels[index]
+}
+
+func (f *filter) Valid(index int) bool {
+	return f.underlying.Valid(index)
+}
+
+func (f *filter) Label(index int) Label {
+	l := f.underlying.Label(index)
+	for _, f := range f.keys {
+		if l.Key() == f {
+			return Label{}
+		}
+	}
+	return l
+}
+
+func (lm listMap) Find(key Key) Label {
+	for _, l := range lm.labels {
+		if l.Key() == key {
+			return l
+		}
+	}
+	return Label{}
+}
+
+func (c mapChain) Find(key Key) Label {
+	for _, src := range c.maps {
+		l := src.Find(key)
+		if l.Valid() {
+			return l
+		}
+	}
+	return Label{}
+}
+
+var emptyList = &list{}
+
+func NewList(labels ...Label) List {
+	if len(labels) == 0 {
+		return emptyList
+	}
+	return &list{labels: labels}
+}
+
+func Filter(l List, keys ...Key) List {
+	if len(keys) == 0 {
+		return l
+	}
+	return &filter{keys: keys, underlying: l}
+}
+
+func NewMap(labels ...Label) Map {
+	return listMap{labels: labels}
+}
+
+func MergeMaps(srcs ...Map) Map {
+	var nonNil []Map
+	for _, src := range srcs {
+		if src != nil {
+			nonNil = append(nonNil, src)
+		}
+	}
+	if len(nonNil) == 1 {
+		return nonNil[0]
+	}
+	return mapChain{maps: nonNil}
+}
diff --git a/vendor/golang.org/x/tools/internal/gocommand/invoke.go b/vendor/golang.org/x/tools/internal/gocommand/invoke.go
new file mode 100644
index 0000000..8659a0c
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/gocommand/invoke.go
@@ -0,0 +1,273 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package gocommand is a helper for calling the go command.
+package gocommand
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	exec "golang.org/x/sys/execabs"
+	"io"
+	"os"
+	"regexp"
+	"strconv"
+	"strings"
+	"sync"
+	"time"
+
+	"golang.org/x/tools/internal/event"
+)
+
+// An Runner will run go command invocations and serialize
+// them if it sees a concurrency error.
+type Runner struct {
+	// once guards the runner initialization.
+	once sync.Once
+
+	// inFlight tracks available workers.
+	inFlight chan struct{}
+
+	// serialized guards the ability to run a go command serially,
+	// to avoid deadlocks when claiming workers.
+	serialized chan struct{}
+}
+
+const maxInFlight = 10
+
+func (runner *Runner) initialize() {
+	runner.once.Do(func() {
+		runner.inFlight = make(chan struct{}, maxInFlight)
+		runner.serialized = make(chan struct{}, 1)
+	})
+}
+
+// 1.13: go: updates to go.mod needed, but contents have changed
+// 1.14: go: updating go.mod: existing contents have changed since last read
+var modConcurrencyError = regexp.MustCompile(`go:.*go.mod.*contents have changed`)
+
+// Run is a convenience wrapper around RunRaw.
+// It returns only stdout and a "friendly" error.
+func (runner *Runner) Run(ctx context.Context, inv Invocation) (*bytes.Buffer, error) {
+	stdout, _, friendly, _ := runner.RunRaw(ctx, inv)
+	return stdout, friendly
+}
+
+// RunPiped runs the invocation serially, always waiting for any concurrent
+// invocations to complete first.
+func (runner *Runner) RunPiped(ctx context.Context, inv Invocation, stdout, stderr io.Writer) error {
+	_, err := runner.runPiped(ctx, inv, stdout, stderr)
+	return err
+}
+
+// RunRaw runs the invocation, serializing requests only if they fight over
+// go.mod changes.
+func (runner *Runner) RunRaw(ctx context.Context, inv Invocation) (*bytes.Buffer, *bytes.Buffer, error, error) {
+	// Make sure the runner is always initialized.
+	runner.initialize()
+
+	// First, try to run the go command concurrently.
+	stdout, stderr, friendlyErr, err := runner.runConcurrent(ctx, inv)
+
+	// If we encounter a load concurrency error, we need to retry serially.
+	if friendlyErr == nil || !modConcurrencyError.MatchString(friendlyErr.Error()) {
+		return stdout, stderr, friendlyErr, err
+	}
+	event.Error(ctx, "Load concurrency error, will retry serially", err)
+
+	// Run serially by calling runPiped.
+	stdout.Reset()
+	stderr.Reset()
+	friendlyErr, err = runner.runPiped(ctx, inv, stdout, stderr)
+	return stdout, stderr, friendlyErr, err
+}
+
+func (runner *Runner) runConcurrent(ctx context.Context, inv Invocation) (*bytes.Buffer, *bytes.Buffer, error, error) {
+	// Wait for 1 worker to become available.
+	select {
+	case <-ctx.Done():
+		return nil, nil, nil, ctx.Err()
+	case runner.inFlight <- struct{}{}:
+		defer func() { <-runner.inFlight }()
+	}
+
+	stdout, stderr := &bytes.Buffer{}, &bytes.Buffer{}
+	friendlyErr, err := inv.runWithFriendlyError(ctx, stdout, stderr)
+	return stdout, stderr, friendlyErr, err
+}
+
+func (runner *Runner) runPiped(ctx context.Context, inv Invocation, stdout, stderr io.Writer) (error, error) {
+	// Make sure the runner is always initialized.
+	runner.initialize()
+
+	// Acquire the serialization lock. This avoids deadlocks between two
+	// runPiped commands.
+	select {
+	case <-ctx.Done():
+		return nil, ctx.Err()
+	case runner.serialized <- struct{}{}:
+		defer func() { <-runner.serialized }()
+	}
+
+	// Wait for all in-progress go commands to return before proceeding,
+	// to avoid load concurrency errors.
+	for i := 0; i < maxInFlight; i++ {
+		select {
+		case <-ctx.Done():
+			return nil, ctx.Err()
+		case runner.inFlight <- struct{}{}:
+			// Make sure we always "return" any workers we took.
+			defer func() { <-runner.inFlight }()
+		}
+	}
+
+	return inv.runWithFriendlyError(ctx, stdout, stderr)
+}
+
+// An Invocation represents a call to the go command.
+type Invocation struct {
+	Verb       string
+	Args       []string
+	BuildFlags []string
+	ModFlag    string
+	ModFile    string
+	Overlay    string
+	// If CleanEnv is set, the invocation will run only with the environment
+	// in Env, not starting with os.Environ.
+	CleanEnv   bool
+	Env        []string
+	WorkingDir string
+	Logf       func(format string, args ...interface{})
+}
+
+func (i *Invocation) runWithFriendlyError(ctx context.Context, stdout, stderr io.Writer) (friendlyError error, rawError error) {
+	rawError = i.run(ctx, stdout, stderr)
+	if rawError != nil {
+		friendlyError = rawError
+		// Check for 'go' executable not being found.
+		if ee, ok := rawError.(*exec.Error); ok && ee.Err == exec.ErrNotFound {
+			friendlyError = fmt.Errorf("go command required, not found: %v", ee)
+		}
+		if ctx.Err() != nil {
+			friendlyError = ctx.Err()
+		}
+		friendlyError = fmt.Errorf("err: %v: stderr: %s", friendlyError, stderr)
+	}
+	return
+}
+
+func (i *Invocation) run(ctx context.Context, stdout, stderr io.Writer) error {
+	log := i.Logf
+	if log == nil {
+		log = func(string, ...interface{}) {}
+	}
+
+	goArgs := []string{i.Verb}
+
+	appendModFile := func() {
+		if i.ModFile != "" {
+			goArgs = append(goArgs, "-modfile="+i.ModFile)
+		}
+	}
+	appendModFlag := func() {
+		if i.ModFlag != "" {
+			goArgs = append(goArgs, "-mod="+i.ModFlag)
+		}
+	}
+	appendOverlayFlag := func() {
+		if i.Overlay != "" {
+			goArgs = append(goArgs, "-overlay="+i.Overlay)
+		}
+	}
+
+	switch i.Verb {
+	case "env", "version":
+		goArgs = append(goArgs, i.Args...)
+	case "mod":
+		// mod needs the sub-verb before flags.
+		goArgs = append(goArgs, i.Args[0])
+		appendModFile()
+		goArgs = append(goArgs, i.Args[1:]...)
+	case "get":
+		goArgs = append(goArgs, i.BuildFlags...)
+		appendModFile()
+		goArgs = append(goArgs, i.Args...)
+
+	default: // notably list and build.
+		goArgs = append(goArgs, i.BuildFlags...)
+		appendModFile()
+		appendModFlag()
+		appendOverlayFlag()
+		goArgs = append(goArgs, i.Args...)
+	}
+	cmd := exec.Command("go", goArgs...)
+	cmd.Stdout = stdout
+	cmd.Stderr = stderr
+	// On darwin the cwd gets resolved to the real path, which breaks anything that
+	// expects the working directory to keep the original path, including the
+	// go command when dealing with modules.
+	// The Go stdlib has a special feature where if the cwd and the PWD are the
+	// same node then it trusts the PWD, so by setting it in the env for the child
+	// process we fix up all the paths returned by the go command.
+	if !i.CleanEnv {
+		cmd.Env = os.Environ()
+	}
+	cmd.Env = append(cmd.Env, i.Env...)
+	if i.WorkingDir != "" {
+		cmd.Env = append(cmd.Env, "PWD="+i.WorkingDir)
+		cmd.Dir = i.WorkingDir
+	}
+	defer func(start time.Time) { log("%s for %v", time.Since(start), cmdDebugStr(cmd)) }(time.Now())
+
+	return runCmdContext(ctx, cmd)
+}
+
+// runCmdContext is like exec.CommandContext except it sends os.Interrupt
+// before os.Kill.
+func runCmdContext(ctx context.Context, cmd *exec.Cmd) error {
+	if err := cmd.Start(); err != nil {
+		return err
+	}
+	resChan := make(chan error, 1)
+	go func() {
+		resChan <- cmd.Wait()
+	}()
+
+	select {
+	case err := <-resChan:
+		return err
+	case <-ctx.Done():
+	}
+	// Cancelled. Interrupt and see if it ends voluntarily.
+	cmd.Process.Signal(os.Interrupt)
+	select {
+	case err := <-resChan:
+		return err
+	case <-time.After(time.Second):
+	}
+	// Didn't shut down in response to interrupt. Kill it hard.
+	cmd.Process.Kill()
+	return <-resChan
+}
+
+func cmdDebugStr(cmd *exec.Cmd) string {
+	env := make(map[string]string)
+	for _, kv := range cmd.Env {
+		split := strings.SplitN(kv, "=", 2)
+		k, v := split[0], split[1]
+		env[k] = v
+	}
+
+	var args []string
+	for _, arg := range cmd.Args {
+		quoted := strconv.Quote(arg)
+		if quoted[1:len(quoted)-1] != arg || strings.Contains(arg, " ") {
+			args = append(args, quoted)
+		} else {
+			args = append(args, arg)
+		}
+	}
+	return fmt.Sprintf("GOROOT=%v GOPATH=%v GO111MODULE=%v GOPROXY=%v PWD=%v %v", env["GOROOT"], env["GOPATH"], env["GO111MODULE"], env["GOPROXY"], env["PWD"], strings.Join(args, " "))
+}
diff --git a/vendor/golang.org/x/tools/internal/gocommand/vendor.go b/vendor/golang.org/x/tools/internal/gocommand/vendor.go
new file mode 100644
index 0000000..5e75bd6
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/gocommand/vendor.go
@@ -0,0 +1,107 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package gocommand
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	"os"
+	"path/filepath"
+	"regexp"
+	"strings"
+	"time"
+
+	"golang.org/x/mod/semver"
+)
+
+// ModuleJSON holds information about a module.
+type ModuleJSON struct {
+	Path      string      // module path
+	Version   string      // module version
+	Versions  []string    // available module versions (with -versions)
+	Replace   *ModuleJSON // replaced by this module
+	Time      *time.Time  // time version was created
+	Update    *ModuleJSON // available update, if any (with -u)
+	Main      bool        // is this the main module?
+	Indirect  bool        // is this module only an indirect dependency of main module?
+	Dir       string      // directory holding files for this module, if any
+	GoMod     string      // path to go.mod file used when loading this module, if any
+	GoVersion string      // go version used in module
+}
+
+var modFlagRegexp = regexp.MustCompile(`-mod[ =](\w+)`)
+
+// VendorEnabled reports whether vendoring is enabled. It takes a *Runner to execute Go commands
+// with the supplied context.Context and Invocation. The Invocation can contain pre-defined fields,
+// of which only Verb and Args are modified to run the appropriate Go command.
+// Inspired by setDefaultBuildMod in modload/init.go
+func VendorEnabled(ctx context.Context, inv Invocation, r *Runner) (*ModuleJSON, bool, error) {
+	mainMod, go114, err := getMainModuleAnd114(ctx, inv, r)
+	if err != nil {
+		return nil, false, err
+	}
+
+	// We check the GOFLAGS to see if there is anything overridden or not.
+	inv.Verb = "env"
+	inv.Args = []string{"GOFLAGS"}
+	stdout, err := r.Run(ctx, inv)
+	if err != nil {
+		return nil, false, err
+	}
+	goflags := string(bytes.TrimSpace(stdout.Bytes()))
+	matches := modFlagRegexp.FindStringSubmatch(goflags)
+	var modFlag string
+	if len(matches) != 0 {
+		modFlag = matches[1]
+	}
+	if modFlag != "" {
+		// Don't override an explicit '-mod=' argument.
+		return mainMod, modFlag == "vendor", nil
+	}
+	if mainMod == nil || !go114 {
+		return mainMod, false, nil
+	}
+	// Check 1.14's automatic vendor mode.
+	if fi, err := os.Stat(filepath.Join(mainMod.Dir, "vendor")); err == nil && fi.IsDir() {
+		if mainMod.GoVersion != "" && semver.Compare("v"+mainMod.GoVersion, "v1.14") >= 0 {
+			// The Go version is at least 1.14, and a vendor directory exists.
+			// Set -mod=vendor by default.
+			return mainMod, true, nil
+		}
+	}
+	return mainMod, false, nil
+}
+
+// getMainModuleAnd114 gets the main module's information and whether the
+// go command in use is 1.14+. This is the information needed to figure out
+// if vendoring should be enabled.
+func getMainModuleAnd114(ctx context.Context, inv Invocation, r *Runner) (*ModuleJSON, bool, error) {
+	const format = `{{.Path}}
+{{.Dir}}
+{{.GoMod}}
+{{.GoVersion}}
+{{range context.ReleaseTags}}{{if eq . "go1.14"}}{{.}}{{end}}{{end}}
+`
+	inv.Verb = "list"
+	inv.Args = []string{"-m", "-f", format}
+	stdout, err := r.Run(ctx, inv)
+	if err != nil {
+		return nil, false, err
+	}
+
+	lines := strings.Split(stdout.String(), "\n")
+	if len(lines) < 5 {
+		return nil, false, fmt.Errorf("unexpected stdout: %q", stdout.String())
+	}
+	mod := &ModuleJSON{
+		Path:      lines[0],
+		Dir:       lines[1],
+		GoMod:     lines[2],
+		GoVersion: lines[3],
+		Main:      true,
+	}
+	return mod, lines[4] == "go1.14", nil
+}
diff --git a/vendor/golang.org/x/tools/internal/gocommand/version.go b/vendor/golang.org/x/tools/internal/gocommand/version.go
new file mode 100644
index 0000000..7130436
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/gocommand/version.go
@@ -0,0 +1,51 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package gocommand
+
+import (
+	"context"
+	"fmt"
+	"strings"
+)
+
+// GoVersion checks the go version by running "go list" with modules off.
+// It returns the X in Go 1.X.
+func GoVersion(ctx context.Context, inv Invocation, r *Runner) (int, error) {
+	inv.Verb = "list"
+	inv.Args = []string{"-e", "-f", `{{context.ReleaseTags}}`, `--`, `unsafe`}
+	inv.Env = append(append([]string{}, inv.Env...), "GO111MODULE=off")
+	// Unset any unneeded flags, and remove them from BuildFlags, if they're
+	// present.
+	inv.ModFile = ""
+	inv.ModFlag = ""
+	var buildFlags []string
+	for _, flag := range inv.BuildFlags {
+		// Flags can be prefixed by one or two dashes.
+		f := strings.TrimPrefix(strings.TrimPrefix(flag, "-"), "-")
+		if strings.HasPrefix(f, "mod=") || strings.HasPrefix(f, "modfile=") {
+			continue
+		}
+		buildFlags = append(buildFlags, flag)
+	}
+	inv.BuildFlags = buildFlags
+	stdoutBytes, err := r.Run(ctx, inv)
+	if err != nil {
+		return 0, err
+	}
+	stdout := stdoutBytes.String()
+	if len(stdout) < 3 {
+		return 0, fmt.Errorf("bad ReleaseTags output: %q", stdout)
+	}
+	// Split up "[go1.1 go1.15]"
+	tags := strings.Fields(stdout[1 : len(stdout)-2])
+	for i := len(tags) - 1; i >= 0; i-- {
+		var version int
+		if _, err := fmt.Sscanf(tags[i], "go1.%d", &version); err != nil {
+			continue
+		}
+		return version, nil
+	}
+	return 0, fmt.Errorf("no parseable ReleaseTags in %v", tags)
+}
diff --git a/vendor/golang.org/x/tools/internal/packagesinternal/packages.go b/vendor/golang.org/x/tools/internal/packagesinternal/packages.go
new file mode 100644
index 0000000..9702094
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/packagesinternal/packages.go
@@ -0,0 +1,28 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package packagesinternal exposes internal-only fields from go/packages.
+package packagesinternal
+
+import (
+	"golang.org/x/tools/internal/gocommand"
+)
+
+var GetForTest = func(p interface{}) string { return "" }
+var GetDepsErrors = func(p interface{}) []*PackageError { return nil }
+
+type PackageError struct {
+	ImportStack []string // shortest path from package named on command line to this one
+	Pos         string   // position of error (if present, file:line:col)
+	Err         string   // the error itself
+}
+
+var GetGoCmdRunner = func(config interface{}) *gocommand.Runner { return nil }
+
+var SetGoCmdRunner = func(config interface{}, runner *gocommand.Runner) {}
+
+var TypecheckCgo int
+
+var SetModFlag = func(config interface{}, value string) {}
+var SetModFile = func(config interface{}, value string) {}
diff --git a/vendor/golang.org/x/tools/internal/typeparams/common.go b/vendor/golang.org/x/tools/internal/typeparams/common.go
new file mode 100644
index 0000000..961d036
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/typeparams/common.go
@@ -0,0 +1,32 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package typeparams provides functions to work indirectly with type parameter
+// data stored in go/ast and go/types objects, while these API are guarded by a
+// build constraint.
+//
+// This package exists to make it easier for tools to work with generic code,
+// while also compiling against older Go versions.
+package typeparams
+
+import (
+	"go/ast"
+	"go/token"
+	"go/types"
+)
+
+// A IndexExprData holds data from both ast.IndexExpr and the new
+// ast.MultiIndexExpr, which was introduced in Go 1.18.
+type IndexExprData struct {
+	X       ast.Expr   // expression
+	Lbrack  token.Pos  // position of "["
+	Indices []ast.Expr // index expressions
+	Rbrack  token.Pos  // position of "]"
+}
+
+// IsTypeParam reports whether t is a type parameter.
+func IsTypeParam(t types.Type) bool {
+	_, ok := t.(*TypeParam)
+	return ok
+}
diff --git a/vendor/golang.org/x/tools/internal/typeparams/enabled_go117.go b/vendor/golang.org/x/tools/internal/typeparams/enabled_go117.go
new file mode 100644
index 0000000..1821239
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/typeparams/enabled_go117.go
@@ -0,0 +1,12 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build !go1.18
+// +build !go1.18
+
+package typeparams
+
+// Enabled reports whether type parameters are enabled in the current build
+// environment.
+const Enabled = false
diff --git a/vendor/golang.org/x/tools/internal/typeparams/enabled_go118.go b/vendor/golang.org/x/tools/internal/typeparams/enabled_go118.go
new file mode 100644
index 0000000..d671488
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/typeparams/enabled_go118.go
@@ -0,0 +1,15 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build go1.18
+// +build go1.18
+
+package typeparams
+
+// Note: this constant is in a separate file as this is the only acceptable
+// diff between the <1.18 API of this package and the 1.18 API.
+
+// Enabled reports whether type parameters are enabled in the current build
+// environment.
+const Enabled = true
diff --git a/vendor/golang.org/x/tools/internal/typeparams/normalize.go b/vendor/golang.org/x/tools/internal/typeparams/normalize.go
new file mode 100644
index 0000000..090f142
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/typeparams/normalize.go
@@ -0,0 +1,216 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package typeparams
+
+import (
+	"errors"
+	"fmt"
+	"go/types"
+	"os"
+	"strings"
+)
+
+//go:generate go run copytermlist.go
+
+const debug = false
+
+var ErrEmptyTypeSet = errors.New("empty type set")
+
+// StructuralTerms returns a slice of terms representing the normalized
+// structural type restrictions of a type parameter, if any.
+//
+// Structural type restrictions of a type parameter are created via
+// non-interface types embedded in its constraint interface (directly, or via a
+// chain of interface embeddings). For example, in the declaration
+//  type T[P interface{~int; m()}] int
+// the structural restriction of the type parameter P is ~int.
+//
+// With interface embedding and unions, the specification of structural type
+// restrictions may be arbitrarily complex. For example, consider the
+// following:
+//
+//  type A interface{ ~string|~[]byte }
+//
+//  type B interface{ int|string }
+//
+//  type C interface { ~string|~int }
+//
+//  type T[P interface{ A|B; C }] int
+//
+// In this example, the structural type restriction of P is ~string|int: A|B
+// expands to ~string|~[]byte|int|string, which reduces to ~string|~[]byte|int,
+// which when intersected with C (~string|~int) yields ~string|int.
+//
+// StructuralTerms computes these expansions and reductions, producing a
+// "normalized" form of the embeddings. A structural restriction is normalized
+// if it is a single union containing no interface terms, and is minimal in the
+// sense that removing any term changes the set of types satisfying the
+// constraint. It is left as a proof for the reader that, modulo sorting, there
+// is exactly one such normalized form.
+//
+// Because the minimal representation always takes this form, StructuralTerms
+// returns a slice of tilde terms corresponding to the terms of the union in
+// the normalized structural restriction. An error is returned if the
+// constraint interface is invalid, exceeds complexity bounds, or has an empty
+// type set. In the latter case, StructuralTerms returns ErrEmptyTypeSet.
+//
+// StructuralTerms makes no guarantees about the order of terms, except that it
+// is deterministic.
+func StructuralTerms(tparam *TypeParam) ([]*Term, error) {
+	constraint := tparam.Constraint()
+	if constraint == nil {
+		return nil, fmt.Errorf("%s has nil constraint", tparam)
+	}
+	iface, _ := constraint.Underlying().(*types.Interface)
+	if iface == nil {
+		return nil, fmt.Errorf("constraint is %T, not *types.Interface", constraint.Underlying())
+	}
+	return InterfaceTermSet(iface)
+}
+
+// InterfaceTermSet computes the normalized terms for a constraint interface,
+// returning an error if the term set cannot be computed or is empty. In the
+// latter case, the error will be ErrEmptyTypeSet.
+//
+// See the documentation of StructuralTerms for more information on
+// normalization.
+func InterfaceTermSet(iface *types.Interface) ([]*Term, error) {
+	return computeTermSet(iface)
+}
+
+// UnionTermSet computes the normalized terms for a union, returning an error
+// if the term set cannot be computed or is empty. In the latter case, the
+// error will be ErrEmptyTypeSet.
+//
+// See the documentation of StructuralTerms for more information on
+// normalization.
+func UnionTermSet(union *Union) ([]*Term, error) {
+	return computeTermSet(union)
+}
+
+func computeTermSet(typ types.Type) ([]*Term, error) {
+	tset, err := computeTermSetInternal(typ, make(map[types.Type]*termSet), 0)
+	if err != nil {
+		return nil, err
+	}
+	if tset.terms.isEmpty() {
+		return nil, ErrEmptyTypeSet
+	}
+	if tset.terms.isAll() {
+		return nil, nil
+	}
+	var terms []*Term
+	for _, term := range tset.terms {
+		terms = append(terms, NewTerm(term.tilde, term.typ))
+	}
+	return terms, nil
+}
+
+// A termSet holds the normalized set of terms for a given type.
+//
+// The name termSet is intentionally distinct from 'type set': a type set is
+// all types that implement a type (and includes method restrictions), whereas
+// a term set just represents the structural restrictions on a type.
+type termSet struct {
+	complete bool
+	terms    termlist
+}
+
+func indentf(depth int, format string, args ...interface{}) {
+	fmt.Fprintf(os.Stderr, strings.Repeat(".", depth)+format+"\n", args...)
+}
+
+func computeTermSetInternal(t types.Type, seen map[types.Type]*termSet, depth int) (res *termSet, err error) {
+	if t == nil {
+		panic("nil type")
+	}
+
+	if debug {
+		indentf(depth, "%s", t.String())
+		defer func() {
+			if err != nil {
+				indentf(depth, "=> %s", err)
+			} else {
+				indentf(depth, "=> %s", res.terms.String())
+			}
+		}()
+	}
+
+	const maxTermCount = 100
+	if tset, ok := seen[t]; ok {
+		if !tset.complete {
+			return nil, fmt.Errorf("cycle detected in the declaration of %s", t)
+		}
+		return tset, nil
+	}
+
+	// Mark the current type as seen to avoid infinite recursion.
+	tset := new(termSet)
+	defer func() {
+		tset.complete = true
+	}()
+	seen[t] = tset
+
+	switch u := t.Underlying().(type) {
+	case *types.Interface:
+		// The term set of an interface is the intersection of the term sets of its
+		// embedded types.
+		tset.terms = allTermlist
+		for i := 0; i < u.NumEmbeddeds(); i++ {
+			embedded := u.EmbeddedType(i)
+			if _, ok := embedded.Underlying().(*TypeParam); ok {
+				return nil, fmt.Errorf("invalid embedded type %T", embedded)
+			}
+			tset2, err := computeTermSetInternal(embedded, seen, depth+1)
+			if err != nil {
+				return nil, err
+			}
+			tset.terms = tset.terms.intersect(tset2.terms)
+		}
+	case *Union:
+		// The term set of a union is the union of term sets of its terms.
+		tset.terms = nil
+		for i := 0; i < u.Len(); i++ {
+			t := u.Term(i)
+			var terms termlist
+			switch t.Type().Underlying().(type) {
+			case *types.Interface:
+				tset2, err := computeTermSetInternal(t.Type(), seen, depth+1)
+				if err != nil {
+					return nil, err
+				}
+				terms = tset2.terms
+			case *TypeParam, *Union:
+				// A stand-alone type parameter or union is not permitted as union
+				// term.
+				return nil, fmt.Errorf("invalid union term %T", t)
+			default:
+				if t.Type() == types.Typ[types.Invalid] {
+					continue
+				}
+				terms = termlist{{t.Tilde(), t.Type()}}
+			}
+			tset.terms = tset.terms.union(terms)
+			if len(tset.terms) > maxTermCount {
+				return nil, fmt.Errorf("exceeded max term count %d", maxTermCount)
+			}
+		}
+	case *TypeParam:
+		panic("unreachable")
+	default:
+		// For all other types, the term set is just a single non-tilde term
+		// holding the type itself.
+		if u != types.Typ[types.Invalid] {
+			tset.terms = termlist{{false, t}}
+		}
+	}
+	return tset, nil
+}
+
+// under is a facade for the go/types internal function of the same name. It is
+// used by typeterm.go.
+func under(t types.Type) types.Type {
+	return t.Underlying()
+}
diff --git a/vendor/golang.org/x/tools/internal/typeparams/termlist.go b/vendor/golang.org/x/tools/internal/typeparams/termlist.go
new file mode 100644
index 0000000..10857d5
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/typeparams/termlist.go
@@ -0,0 +1,172 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Code generated by copytermlist.go DO NOT EDIT.
+
+package typeparams
+
+import (
+	"bytes"
+	"go/types"
+)
+
+// A termlist represents the type set represented by the union
+// t1 ∪ y2 ∪ ... tn of the type sets of the terms t1 to tn.
+// A termlist is in normal form if all terms are disjoint.
+// termlist operations don't require the operands to be in
+// normal form.
+type termlist []*term
+
+// allTermlist represents the set of all types.
+// It is in normal form.
+var allTermlist = termlist{new(term)}
+
+// String prints the termlist exactly (without normalization).
+func (xl termlist) String() string {
+	if len(xl) == 0 {
+		return "∅"
+	}
+	var buf bytes.Buffer
+	for i, x := range xl {
+		if i > 0 {
+			buf.WriteString(" ∪ ")
+		}
+		buf.WriteString(x.String())
+	}
+	return buf.String()
+}
+
+// isEmpty reports whether the termlist xl represents the empty set of types.
+func (xl termlist) isEmpty() bool {
+	// If there's a non-nil term, the entire list is not empty.
+	// If the termlist is in normal form, this requires at most
+	// one iteration.
+	for _, x := range xl {
+		if x != nil {
+			return false
+		}
+	}
+	return true
+}
+
+// isAll reports whether the termlist xl represents the set of all types.
+func (xl termlist) isAll() bool {
+	// If there's a 𝓤 term, the entire list is 𝓤.
+	// If the termlist is in normal form, this requires at most
+	// one iteration.
+	for _, x := range xl {
+		if x != nil && x.typ == nil {
+			return true
+		}
+	}
+	return false
+}
+
+// norm returns the normal form of xl.
+func (xl termlist) norm() termlist {
+	// Quadratic algorithm, but good enough for now.
+	// TODO(gri) fix asymptotic performance
+	used := make([]bool, len(xl))
+	var rl termlist
+	for i, xi := range xl {
+		if xi == nil || used[i] {
+			continue
+		}
+		for j := i + 1; j < len(xl); j++ {
+			xj := xl[j]
+			if xj == nil || used[j] {
+				continue
+			}
+			if u1, u2 := xi.union(xj); u2 == nil {
+				// If we encounter a 𝓤 term, the entire list is 𝓤.
+				// Exit early.
+				// (Note that this is not just an optimization;
+				// if we continue, we may end up with a 𝓤 term
+				// and other terms and the result would not be
+				// in normal form.)
+				if u1.typ == nil {
+					return allTermlist
+				}
+				xi = u1
+				used[j] = true // xj is now unioned into xi - ignore it in future iterations
+			}
+		}
+		rl = append(rl, xi)
+	}
+	return rl
+}
+
+// If the type set represented by xl is specified by a single (non-𝓤) term,
+// structuralType returns that type. Otherwise it returns nil.
+func (xl termlist) structuralType() types.Type {
+	if nl := xl.norm(); len(nl) == 1 {
+		return nl[0].typ // if nl.isAll() then typ is nil, which is ok
+	}
+	return nil
+}
+
+// union returns the union xl ∪ yl.
+func (xl termlist) union(yl termlist) termlist {
+	return append(xl, yl...).norm()
+}
+
+// intersect returns the intersection xl ∩ yl.
+func (xl termlist) intersect(yl termlist) termlist {
+	if xl.isEmpty() || yl.isEmpty() {
+		return nil
+	}
+
+	// Quadratic algorithm, but good enough for now.
+	// TODO(gri) fix asymptotic performance
+	var rl termlist
+	for _, x := range xl {
+		for _, y := range yl {
+			if r := x.intersect(y); r != nil {
+				rl = append(rl, r)
+			}
+		}
+	}
+	return rl.norm()
+}
+
+// equal reports whether xl and yl represent the same type set.
+func (xl termlist) equal(yl termlist) bool {
+	// TODO(gri) this should be more efficient
+	return xl.subsetOf(yl) && yl.subsetOf(xl)
+}
+
+// includes reports whether t ∈ xl.
+func (xl termlist) includes(t types.Type) bool {
+	for _, x := range xl {
+		if x.includes(t) {
+			return true
+		}
+	}
+	return false
+}
+
+// supersetOf reports whether y ⊆ xl.
+func (xl termlist) supersetOf(y *term) bool {
+	for _, x := range xl {
+		if y.subsetOf(x) {
+			return true
+		}
+	}
+	return false
+}
+
+// subsetOf reports whether xl ⊆ yl.
+func (xl termlist) subsetOf(yl termlist) bool {
+	if yl.isEmpty() {
+		return xl.isEmpty()
+	}
+
+	// each term x of xl must be a subset of yl
+	for _, x := range xl {
+		if !yl.supersetOf(x) {
+			return false // x is not a subset yl
+		}
+	}
+	return true
+}
diff --git a/vendor/golang.org/x/tools/internal/typeparams/typeparams_go117.go b/vendor/golang.org/x/tools/internal/typeparams/typeparams_go117.go
new file mode 100644
index 0000000..e509daf
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/typeparams/typeparams_go117.go
@@ -0,0 +1,224 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build !go1.18
+// +build !go1.18
+
+package typeparams
+
+import (
+	"go/ast"
+	"go/token"
+	"go/types"
+)
+
+func unsupported() {
+	panic("type parameters are unsupported at this go version")
+}
+
+// GetIndexExprData extracts data from *ast.IndexExpr nodes.
+// For other nodes, GetIndexExprData returns nil.
+func GetIndexExprData(n ast.Node) *IndexExprData {
+	if e, _ := n.(*ast.IndexExpr); e != nil {
+		return &IndexExprData{
+			X:       e.X,
+			Lbrack:  e.Lbrack,
+			Indices: []ast.Expr{e.Index},
+			Rbrack:  e.Rbrack,
+		}
+	}
+	return nil
+}
+
+// PackIndexExpr returns an *ast.IndexExpr with the given index.
+// Calling PackIndexExpr with len(indices) != 1 will panic.
+func PackIndexExpr(x ast.Expr, lbrack token.Pos, indices []ast.Expr, rbrack token.Pos) ast.Expr {
+	switch len(indices) {
+	case 0:
+		panic("empty indices")
+	case 1:
+		return &ast.IndexExpr{
+			X:      x,
+			Lbrack: lbrack,
+			Index:  indices[0],
+			Rbrack: rbrack,
+		}
+	default:
+		panic("cannot pack multiple indices at this go version")
+	}
+}
+
+// IndexListExpr is a placeholder type, as type parameters are not supported at
+// this Go version. Its methods panic on use.
+type IndexListExpr struct {
+	ast.Expr
+	X       ast.Expr   // expression
+	Lbrack  token.Pos  // position of "["
+	Indices []ast.Expr // index expressions
+	Rbrack  token.Pos  // position of "]"
+}
+
+// ForTypeSpec returns an empty field list, as type parameters on not supported
+// at this Go version.
+func ForTypeSpec(*ast.TypeSpec) *ast.FieldList {
+	return nil
+}
+
+// ForFuncType returns an empty field list, as type parameters are not
+// supported at this Go version.
+func ForFuncType(*ast.FuncType) *ast.FieldList {
+	return nil
+}
+
+// TypeParam is a placeholder type, as type parameters are not supported at
+// this Go version. Its methods panic on use.
+type TypeParam struct{ types.Type }
+
+func (*TypeParam) Index() int             { unsupported(); return 0 }
+func (*TypeParam) Constraint() types.Type { unsupported(); return nil }
+func (*TypeParam) Obj() *types.TypeName   { unsupported(); return nil }
+
+// TypeParamList is a placeholder for an empty type parameter list.
+type TypeParamList struct{}
+
+func (*TypeParamList) Len() int          { return 0 }
+func (*TypeParamList) At(int) *TypeParam { unsupported(); return nil }
+
+// TypeList is a placeholder for an empty type list.
+type TypeList struct{}
+
+func (*TypeList) Len() int          { return 0 }
+func (*TypeList) At(int) types.Type { unsupported(); return nil }
+
+// NewTypeParam is unsupported at this Go version, and panics.
+func NewTypeParam(name *types.TypeName, constraint types.Type) *TypeParam {
+	unsupported()
+	return nil
+}
+
+// SetTypeParamConstraint is unsupported at this Go version, and panics.
+func SetTypeParamConstraint(tparam *TypeParam, constraint types.Type) {
+	unsupported()
+}
+
+// NewSignatureType calls types.NewSignature, panicking if recvTypeParams or
+// typeParams is non-empty.
+func NewSignatureType(recv *types.Var, recvTypeParams, typeParams []*TypeParam, params, results *types.Tuple, variadic bool) *types.Signature {
+	if len(recvTypeParams) != 0 || len(typeParams) != 0 {
+		panic("signatures cannot have type parameters at this Go version")
+	}
+	return types.NewSignature(recv, params, results, variadic)
+}
+
+// ForSignature returns an empty slice.
+func ForSignature(*types.Signature) *TypeParamList {
+	return nil
+}
+
+// RecvTypeParams returns a nil slice.
+func RecvTypeParams(sig *types.Signature) *TypeParamList {
+	return nil
+}
+
+// IsComparable returns false, as no interfaces are type-restricted at this Go
+// version.
+func IsComparable(*types.Interface) bool {
+	return false
+}
+
+// IsMethodSet returns true, as no interfaces are type-restricted at this Go
+// version.
+func IsMethodSet(*types.Interface) bool {
+	return true
+}
+
+// IsImplicit returns false, as no interfaces are implicit at this Go version.
+func IsImplicit(*types.Interface) bool {
+	return false
+}
+
+// MarkImplicit does nothing, because this Go version does not have implicit
+// interfaces.
+func MarkImplicit(*types.Interface) {}
+
+// ForNamed returns an empty type parameter list, as type parameters are not
+// supported at this Go version.
+func ForNamed(*types.Named) *TypeParamList {
+	return nil
+}
+
+// SetForNamed panics if tparams is non-empty.
+func SetForNamed(_ *types.Named, tparams []*TypeParam) {
+	if len(tparams) > 0 {
+		unsupported()
+	}
+}
+
+// NamedTypeArgs returns nil.
+func NamedTypeArgs(*types.Named) *TypeList {
+	return nil
+}
+
+// NamedTypeOrigin is the identity method at this Go version.
+func NamedTypeOrigin(named *types.Named) types.Type {
+	return named
+}
+
+// Term holds information about a structural type restriction.
+type Term struct {
+	tilde bool
+	typ   types.Type
+}
+
+func (m *Term) Tilde() bool      { return m.tilde }
+func (m *Term) Type() types.Type { return m.typ }
+func (m *Term) String() string {
+	pre := ""
+	if m.tilde {
+		pre = "~"
+	}
+	return pre + m.typ.String()
+}
+
+// NewTerm is unsupported at this Go version, and panics.
+func NewTerm(tilde bool, typ types.Type) *Term {
+	return &Term{tilde, typ}
+}
+
+// Union is a placeholder type, as type parameters are not supported at this Go
+// version. Its methods panic on use.
+type Union struct{ types.Type }
+
+func (*Union) Len() int         { return 0 }
+func (*Union) Term(i int) *Term { unsupported(); return nil }
+
+// NewUnion is unsupported at this Go version, and panics.
+func NewUnion(terms []*Term) *Union {
+	unsupported()
+	return nil
+}
+
+// InitInstanceInfo is a noop at this Go version.
+func InitInstanceInfo(*types.Info) {}
+
+// Instance is a placeholder type, as type parameters are not supported at this
+// Go version.
+type Instance struct {
+	TypeArgs *TypeList
+	Type     types.Type
+}
+
+// GetInstances returns a nil map, as type parameters are not supported at this
+// Go version.
+func GetInstances(info *types.Info) map[*ast.Ident]Instance { return nil }
+
+// Context is a placeholder type, as type parameters are not supported at
+// this Go version.
+type Context struct{}
+
+// Instantiate is unsupported on this Go version, and panics.
+func Instantiate(ctxt *Context, typ types.Type, targs []types.Type, validate bool) (types.Type, error) {
+	unsupported()
+	return nil, nil
+}
diff --git a/vendor/golang.org/x/tools/internal/typeparams/typeparams_go118.go b/vendor/golang.org/x/tools/internal/typeparams/typeparams_go118.go
new file mode 100644
index 0000000..e45896f
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/typeparams/typeparams_go118.go
@@ -0,0 +1,196 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build go1.18
+// +build go1.18
+
+package typeparams
+
+import (
+	"go/ast"
+	"go/token"
+	"go/types"
+)
+
+// GetIndexExprData extracts data from AST nodes that represent index
+// expressions.
+//
+// For an ast.IndexExpr, the resulting IndexExprData will have exactly one
+// index expression. For an ast.IndexListExpr (go1.18+), it may have a
+// variable number of index expressions.
+//
+// For nodes that don't represent index expressions, GetIndexExprData returns
+// nil.
+// TODO(rfindley): remove this function in favor of using the alias below.
+func GetIndexExprData(n ast.Node) *IndexExprData {
+	switch e := n.(type) {
+	case *ast.IndexExpr:
+		return &IndexExprData{
+			X:       e.X,
+			Lbrack:  e.Lbrack,
+			Indices: []ast.Expr{e.Index},
+			Rbrack:  e.Rbrack,
+		}
+	case *ast.IndexListExpr:
+		return (*IndexExprData)(e)
+	}
+	return nil
+}
+
+// PackIndexExpr returns an *ast.IndexExpr or *ast.IndexListExpr, depending on
+// the cardinality of indices. Calling PackIndexExpr with len(indices) == 0
+// will panic.
+func PackIndexExpr(x ast.Expr, lbrack token.Pos, indices []ast.Expr, rbrack token.Pos) ast.Expr {
+	switch len(indices) {
+	case 0:
+		panic("empty indices")
+	case 1:
+		return &ast.IndexExpr{
+			X:      x,
+			Lbrack: lbrack,
+			Index:  indices[0],
+			Rbrack: rbrack,
+		}
+	default:
+		return &ast.IndexListExpr{
+			X:       x,
+			Lbrack:  lbrack,
+			Indices: indices,
+			Rbrack:  rbrack,
+		}
+	}
+}
+
+// IndexListExpr is an alias for ast.IndexListExpr.
+type IndexListExpr = ast.IndexListExpr
+
+// ForTypeSpec returns n.TypeParams.
+func ForTypeSpec(n *ast.TypeSpec) *ast.FieldList {
+	if n == nil {
+		return nil
+	}
+	return n.TypeParams
+}
+
+// ForFuncType returns n.TypeParams.
+func ForFuncType(n *ast.FuncType) *ast.FieldList {
+	if n == nil {
+		return nil
+	}
+	return n.TypeParams
+}
+
+// TypeParam is an alias for types.TypeParam
+type TypeParam = types.TypeParam
+
+// TypeParamList is an alias for types.TypeParamList
+type TypeParamList = types.TypeParamList
+
+// TypeList is an alias for types.TypeList
+type TypeList = types.TypeList
+
+// NewTypeParam calls types.NewTypeParam.
+func NewTypeParam(name *types.TypeName, constraint types.Type) *TypeParam {
+	return types.NewTypeParam(name, constraint)
+}
+
+// SetTypeParamConstraint calls tparam.SetConstraint(constraint).
+func SetTypeParamConstraint(tparam *TypeParam, constraint types.Type) {
+	tparam.SetConstraint(constraint)
+}
+
+// NewSignatureType calls types.NewSignatureType.
+func NewSignatureType(recv *types.Var, recvTypeParams, typeParams []*TypeParam, params, results *types.Tuple, variadic bool) *types.Signature {
+	return types.NewSignatureType(recv, recvTypeParams, typeParams, params, results, variadic)
+}
+
+// ForSignature returns sig.TypeParams()
+func ForSignature(sig *types.Signature) *TypeParamList {
+	return sig.TypeParams()
+}
+
+// RecvTypeParams returns sig.RecvTypeParams().
+func RecvTypeParams(sig *types.Signature) *TypeParamList {
+	return sig.RecvTypeParams()
+}
+
+// IsComparable calls iface.IsComparable().
+func IsComparable(iface *types.Interface) bool {
+	return iface.IsComparable()
+}
+
+// IsMethodSet calls iface.IsMethodSet().
+func IsMethodSet(iface *types.Interface) bool {
+	return iface.IsMethodSet()
+}
+
+// IsImplicit calls iface.IsImplicit().
+func IsImplicit(iface *types.Interface) bool {
+	return iface.IsImplicit()
+}
+
+// MarkImplicit calls iface.MarkImplicit().
+func MarkImplicit(iface *types.Interface) {
+	iface.MarkImplicit()
+}
+
+// ForNamed extracts the (possibly empty) type parameter object list from
+// named.
+func ForNamed(named *types.Named) *TypeParamList {
+	return named.TypeParams()
+}
+
+// SetForNamed sets the type params tparams on n. Each tparam must be of
+// dynamic type *types.TypeParam.
+func SetForNamed(n *types.Named, tparams []*TypeParam) {
+	n.SetTypeParams(tparams)
+}
+
+// NamedTypeArgs returns named.TypeArgs().
+func NamedTypeArgs(named *types.Named) *TypeList {
+	return named.TypeArgs()
+}
+
+// NamedTypeOrigin returns named.Orig().
+func NamedTypeOrigin(named *types.Named) types.Type {
+	return named.Origin()
+}
+
+// Term is an alias for types.Term.
+type Term = types.Term
+
+// NewTerm calls types.NewTerm.
+func NewTerm(tilde bool, typ types.Type) *Term {
+	return types.NewTerm(tilde, typ)
+}
+
+// Union is an alias for types.Union
+type Union = types.Union
+
+// NewUnion calls types.NewUnion.
+func NewUnion(terms []*Term) *Union {
+	return types.NewUnion(terms)
+}
+
+// InitInstanceInfo initializes info to record information about type and
+// function instances.
+func InitInstanceInfo(info *types.Info) {
+	info.Instances = make(map[*ast.Ident]types.Instance)
+}
+
+// Instance is an alias for types.Instance.
+type Instance = types.Instance
+
+// GetInstances returns info.Instances.
+func GetInstances(info *types.Info) map[*ast.Ident]Instance {
+	return info.Instances
+}
+
+// Context is an alias for types.Context.
+type Context = types.Context
+
+// Instantiate calls types.Instantiate.
+func Instantiate(ctxt *Context, typ types.Type, targs []types.Type, validate bool) (types.Type, error) {
+	return types.Instantiate(ctxt, typ, targs, validate)
+}
diff --git a/vendor/golang.org/x/tools/internal/typeparams/typeterm.go b/vendor/golang.org/x/tools/internal/typeparams/typeterm.go
new file mode 100644
index 0000000..7ddee28
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/typeparams/typeterm.go
@@ -0,0 +1,170 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Code generated by copytermlist.go DO NOT EDIT.
+
+package typeparams
+
+import "go/types"
+
+// A term describes elementary type sets:
+//
+//   ∅:  (*term)(nil)     == ∅                      // set of no types (empty set)
+//   𝓤:  &term{}          == 𝓤                      // set of all types (𝓤niverse)
+//   T:  &term{false, T}  == {T}                    // set of type T
+//  ~t:  &term{true, t}   == {t' | under(t') == t}  // set of types with underlying type t
+//
+type term struct {
+	tilde bool // valid if typ != nil
+	typ   types.Type
+}
+
+func (x *term) String() string {
+	switch {
+	case x == nil:
+		return "∅"
+	case x.typ == nil:
+		return "𝓤"
+	case x.tilde:
+		return "~" + x.typ.String()
+	default:
+		return x.typ.String()
+	}
+}
+
+// equal reports whether x and y represent the same type set.
+func (x *term) equal(y *term) bool {
+	// easy cases
+	switch {
+	case x == nil || y == nil:
+		return x == y
+	case x.typ == nil || y.typ == nil:
+		return x.typ == y.typ
+	}
+	// ∅ ⊂ x, y ⊂ 𝓤
+
+	return x.tilde == y.tilde && types.Identical(x.typ, y.typ)
+}
+
+// union returns the union x ∪ y: zero, one, or two non-nil terms.
+func (x *term) union(y *term) (_, _ *term) {
+	// easy cases
+	switch {
+	case x == nil && y == nil:
+		return nil, nil // ∅ ∪ ∅ == ∅
+	case x == nil:
+		return y, nil // ∅ ∪ y == y
+	case y == nil:
+		return x, nil // x ∪ ∅ == x
+	case x.typ == nil:
+		return x, nil // 𝓤 ∪ y == 𝓤
+	case y.typ == nil:
+		return y, nil // x ∪ 𝓤 == 𝓤
+	}
+	// ∅ ⊂ x, y ⊂ 𝓤
+
+	if x.disjoint(y) {
+		return x, y // x ∪ y == (x, y) if x ∩ y == ∅
+	}
+	// x.typ == y.typ
+
+	// ~t ∪ ~t == ~t
+	// ~t ∪  T == ~t
+	//  T ∪ ~t == ~t
+	//  T ∪  T ==  T
+	if x.tilde || !y.tilde {
+		return x, nil
+	}
+	return y, nil
+}
+
+// intersect returns the intersection x ∩ y.
+func (x *term) intersect(y *term) *term {
+	// easy cases
+	switch {
+	case x == nil || y == nil:
+		return nil // ∅ ∩ y == ∅ and ∩ ∅ == ∅
+	case x.typ == nil:
+		return y // 𝓤 ∩ y == y
+	case y.typ == nil:
+		return x // x ∩ 𝓤 == x
+	}
+	// ∅ ⊂ x, y ⊂ 𝓤
+
+	if x.disjoint(y) {
+		return nil // x ∩ y == ∅ if x ∩ y == ∅
+	}
+	// x.typ == y.typ
+
+	// ~t ∩ ~t == ~t
+	// ~t ∩  T ==  T
+	//  T ∩ ~t ==  T
+	//  T ∩  T ==  T
+	if !x.tilde || y.tilde {
+		return x
+	}
+	return y
+}
+
+// includes reports whether t ∈ x.
+func (x *term) includes(t types.Type) bool {
+	// easy cases
+	switch {
+	case x == nil:
+		return false // t ∈ ∅ == false
+	case x.typ == nil:
+		return true // t ∈ 𝓤 == true
+	}
+	// ∅ ⊂ x ⊂ 𝓤
+
+	u := t
+	if x.tilde {
+		u = under(u)
+	}
+	return types.Identical(x.typ, u)
+}
+
+// subsetOf reports whether x ⊆ y.
+func (x *term) subsetOf(y *term) bool {
+	// easy cases
+	switch {
+	case x == nil:
+		return true // ∅ ⊆ y == true
+	case y == nil:
+		return false // x ⊆ ∅ == false since x != ∅
+	case y.typ == nil:
+		return true // x ⊆ 𝓤 == true
+	case x.typ == nil:
+		return false // 𝓤 ⊆ y == false since y != 𝓤
+	}
+	// ∅ ⊂ x, y ⊂ 𝓤
+
+	if x.disjoint(y) {
+		return false // x ⊆ y == false if x ∩ y == ∅
+	}
+	// x.typ == y.typ
+
+	// ~t ⊆ ~t == true
+	// ~t ⊆ T == false
+	//  T ⊆ ~t == true
+	//  T ⊆  T == true
+	return !x.tilde || y.tilde
+}
+
+// disjoint reports whether x ∩ y == ∅.
+// x.typ and y.typ must not be nil.
+func (x *term) disjoint(y *term) bool {
+	if debug && (x.typ == nil || y.typ == nil) {
+		panic("invalid argument(s)")
+	}
+	ux := x.typ
+	if y.tilde {
+		ux = under(ux)
+	}
+	uy := y.typ
+	if x.tilde {
+		uy = under(uy)
+	}
+	return !types.Identical(ux, uy)
+}
diff --git a/vendor/golang.org/x/tools/internal/typesinternal/errorcode.go b/vendor/golang.org/x/tools/internal/typesinternal/errorcode.go
new file mode 100644
index 0000000..fa2834e
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/typesinternal/errorcode.go
@@ -0,0 +1,1368 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package typesinternal
+
+//go:generate stringer -type=ErrorCode
+
+type ErrorCode int
+
+// This file defines the error codes that can be produced during type-checking.
+// Collectively, these codes provide an identifier that may be used to
+// implement special handling for certain types of errors.
+//
+// Error codes should be fine-grained enough that the exact nature of the error
+// can be easily determined, but coarse enough that they are not an
+// implementation detail of the type checking algorithm. As a rule-of-thumb,
+// errors should be considered equivalent if there is a theoretical refactoring
+// of the type checker in which they are emitted in exactly one place. For
+// example, the type checker emits different error messages for "too many
+// arguments" and "too few arguments", but one can imagine an alternative type
+// checker where this check instead just emits a single "wrong number of
+// arguments", so these errors should have the same code.
+//
+// Error code names should be as brief as possible while retaining accuracy and
+// distinctiveness. In most cases names should start with an adjective
+// describing the nature of the error (e.g. "invalid", "unused", "misplaced"),
+// and end with a noun identifying the relevant language object. For example,
+// "DuplicateDecl" or "InvalidSliceExpr". For brevity, naming follows the
+// convention that "bad" implies a problem with syntax, and "invalid" implies a
+// problem with types.
+
+const (
+	_ ErrorCode = iota
+
+	// Test is reserved for errors that only apply while in self-test mode.
+	Test
+
+	/* package names */
+
+	// BlankPkgName occurs when a package name is the blank identifier "_".
+	//
+	// Per the spec:
+	//  "The PackageName must not be the blank identifier."
+	BlankPkgName
+
+	// MismatchedPkgName occurs when a file's package name doesn't match the
+	// package name already established by other files.
+	MismatchedPkgName
+
+	// InvalidPkgUse occurs when a package identifier is used outside of a
+	// selector expression.
+	//
+	// Example:
+	//  import "fmt"
+	//
+	//  var _ = fmt
+	InvalidPkgUse
+
+	/* imports */
+
+	// BadImportPath occurs when an import path is not valid.
+	BadImportPath
+
+	// BrokenImport occurs when importing a package fails.
+	//
+	// Example:
+	//  import "amissingpackage"
+	BrokenImport
+
+	// ImportCRenamed occurs when the special import "C" is renamed. "C" is a
+	// pseudo-package, and must not be renamed.
+	//
+	// Example:
+	//  import _ "C"
+	ImportCRenamed
+
+	// UnusedImport occurs when an import is unused.
+	//
+	// Example:
+	//  import "fmt"
+	//
+	//  func main() {}
+	UnusedImport
+
+	/* initialization */
+
+	// InvalidInitCycle occurs when an invalid cycle is detected within the
+	// initialization graph.
+	//
+	// Example:
+	//  var x int = f()
+	//
+	//  func f() int { return x }
+	InvalidInitCycle
+
+	/* decls */
+
+	// DuplicateDecl occurs when an identifier is declared multiple times.
+	//
+	// Example:
+	//  var x = 1
+	//  var x = 2
+	DuplicateDecl
+
+	// InvalidDeclCycle occurs when a declaration cycle is not valid.
+	//
+	// Example:
+	//  import "unsafe"
+	//
+	//  type T struct {
+	//  	a [n]int
+	//  }
+	//
+	//  var n = unsafe.Sizeof(T{})
+	InvalidDeclCycle
+
+	// InvalidTypeCycle occurs when a cycle in type definitions results in a
+	// type that is not well-defined.
+	//
+	// Example:
+	//  import "unsafe"
+	//
+	//  type T [unsafe.Sizeof(T{})]int
+	InvalidTypeCycle
+
+	/* decls > const */
+
+	// InvalidConstInit occurs when a const declaration has a non-constant
+	// initializer.
+	//
+	// Example:
+	//  var x int
+	//  const _ = x
+	InvalidConstInit
+
+	// InvalidConstVal occurs when a const value cannot be converted to its
+	// target type.
+	//
+	// TODO(findleyr): this error code and example are not very clear. Consider
+	// removing it.
+	//
+	// Example:
+	//  const _ = 1 << "hello"
+	InvalidConstVal
+
+	// InvalidConstType occurs when the underlying type in a const declaration
+	// is not a valid constant type.
+	//
+	// Example:
+	//  const c *int = 4
+	InvalidConstType
+
+	/* decls > var (+ other variable assignment codes) */
+
+	// UntypedNil occurs when the predeclared (untyped) value nil is used to
+	// initialize a variable declared without an explicit type.
+	//
+	// Example:
+	//  var x = nil
+	UntypedNil
+
+	// WrongAssignCount occurs when the number of values on the right-hand side
+	// of an assignment or or initialization expression does not match the number
+	// of variables on the left-hand side.
+	//
+	// Example:
+	//  var x = 1, 2
+	WrongAssignCount
+
+	// UnassignableOperand occurs when the left-hand side of an assignment is
+	// not assignable.
+	//
+	// Example:
+	//  func f() {
+	//  	const c = 1
+	//  	c = 2
+	//  }
+	UnassignableOperand
+
+	// NoNewVar occurs when a short variable declaration (':=') does not declare
+	// new variables.
+	//
+	// Example:
+	//  func f() {
+	//  	x := 1
+	//  	x := 2
+	//  }
+	NoNewVar
+
+	// MultiValAssignOp occurs when an assignment operation (+=, *=, etc) does
+	// not have single-valued left-hand or right-hand side.
+	//
+	// Per the spec:
+	//  "In assignment operations, both the left- and right-hand expression lists
+	//  must contain exactly one single-valued expression"
+	//
+	// Example:
+	//  func f() int {
+	//  	x, y := 1, 2
+	//  	x, y += 1
+	//  	return x + y
+	//  }
+	MultiValAssignOp
+
+	// InvalidIfaceAssign occurs when a value of type T is used as an
+	// interface, but T does not implement a method of the expected interface.
+	//
+	// Example:
+	//  type I interface {
+	//  	f()
+	//  }
+	//
+	//  type T int
+	//
+	//  var x I = T(1)
+	InvalidIfaceAssign
+
+	// InvalidChanAssign occurs when a chan assignment is invalid.
+	//
+	// Per the spec, a value x is assignable to a channel type T if:
+	//  "x is a bidirectional channel value, T is a channel type, x's type V and
+	//  T have identical element types, and at least one of V or T is not a
+	//  defined type."
+	//
+	// Example:
+	//  type T1 chan int
+	//  type T2 chan int
+	//
+	//  var x T1
+	//  // Invalid assignment because both types are named
+	//  var _ T2 = x
+	InvalidChanAssign
+
+	// IncompatibleAssign occurs when the type of the right-hand side expression
+	// in an assignment cannot be assigned to the type of the variable being
+	// assigned.
+	//
+	// Example:
+	//  var x []int
+	//  var _ int = x
+	IncompatibleAssign
+
+	// UnaddressableFieldAssign occurs when trying to assign to a struct field
+	// in a map value.
+	//
+	// Example:
+	//  func f() {
+	//  	m := make(map[string]struct{i int})
+	//  	m["foo"].i = 42
+	//  }
+	UnaddressableFieldAssign
+
+	/* decls > type (+ other type expression codes) */
+
+	// NotAType occurs when the identifier used as the underlying type in a type
+	// declaration or the right-hand side of a type alias does not denote a type.
+	//
+	// Example:
+	//  var S = 2
+	//
+	//  type T S
+	NotAType
+
+	// InvalidArrayLen occurs when an array length is not a constant value.
+	//
+	// Example:
+	//  var n = 3
+	//  var _ = [n]int{}
+	InvalidArrayLen
+
+	// BlankIfaceMethod occurs when a method name is '_'.
+	//
+	// Per the spec:
+	//  "The name of each explicitly specified method must be unique and not
+	//  blank."
+	//
+	// Example:
+	//  type T interface {
+	//  	_(int)
+	//  }
+	BlankIfaceMethod
+
+	// IncomparableMapKey occurs when a map key type does not support the == and
+	// != operators.
+	//
+	// Per the spec:
+	//  "The comparison operators == and != must be fully defined for operands of
+	//  the key type; thus the key type must not be a function, map, or slice."
+	//
+	// Example:
+	//  var x map[T]int
+	//
+	//  type T []int
+	IncomparableMapKey
+
+	// InvalidIfaceEmbed occurs when a non-interface type is embedded in an
+	// interface.
+	//
+	// Example:
+	//  type T struct {}
+	//
+	//  func (T) m()
+	//
+	//  type I interface {
+	//  	T
+	//  }
+	InvalidIfaceEmbed
+
+	// InvalidPtrEmbed occurs when an embedded field is of the pointer form *T,
+	// and T itself is itself a pointer, an unsafe.Pointer, or an interface.
+	//
+	// Per the spec:
+	//  "An embedded field must be specified as a type name T or as a pointer to
+	//  a non-interface type name *T, and T itself may not be a pointer type."
+	//
+	// Example:
+	//  type T *int
+	//
+	//  type S struct {
+	//  	*T
+	//  }
+	InvalidPtrEmbed
+
+	/* decls > func and method */
+
+	// BadRecv occurs when a method declaration does not have exactly one
+	// receiver parameter.
+	//
+	// Example:
+	//  func () _() {}
+	BadRecv
+
+	// InvalidRecv occurs when a receiver type expression is not of the form T
+	// or *T, or T is a pointer type.
+	//
+	// Example:
+	//  type T struct {}
+	//
+	//  func (**T) m() {}
+	InvalidRecv
+
+	// DuplicateFieldAndMethod occurs when an identifier appears as both a field
+	// and method name.
+	//
+	// Example:
+	//  type T struct {
+	//  	m int
+	//  }
+	//
+	//  func (T) m() {}
+	DuplicateFieldAndMethod
+
+	// DuplicateMethod occurs when two methods on the same receiver type have
+	// the same name.
+	//
+	// Example:
+	//  type T struct {}
+	//  func (T) m() {}
+	//  func (T) m(i int) int { return i }
+	DuplicateMethod
+
+	/* decls > special */
+
+	// InvalidBlank occurs when a blank identifier is used as a value or type.
+	//
+	// Per the spec:
+	//  "The blank identifier may appear as an operand only on the left-hand side
+	//  of an assignment."
+	//
+	// Example:
+	//  var x = _
+	InvalidBlank
+
+	// InvalidIota occurs when the predeclared identifier iota is used outside
+	// of a constant declaration.
+	//
+	// Example:
+	//  var x = iota
+	InvalidIota
+
+	// MissingInitBody occurs when an init function is missing its body.
+	//
+	// Example:
+	//  func init()
+	MissingInitBody
+
+	// InvalidInitSig occurs when an init function declares parameters or
+	// results.
+	//
+	// Example:
+	//  func init() int { return 1 }
+	InvalidInitSig
+
+	// InvalidInitDecl occurs when init is declared as anything other than a
+	// function.
+	//
+	// Example:
+	//  var init = 1
+	InvalidInitDecl
+
+	// InvalidMainDecl occurs when main is declared as anything other than a
+	// function, in a main package.
+	InvalidMainDecl
+
+	/* exprs */
+
+	// TooManyValues occurs when a function returns too many values for the
+	// expression context in which it is used.
+	//
+	// Example:
+	//  func ReturnTwo() (int, int) {
+	//  	return 1, 2
+	//  }
+	//
+	//  var x = ReturnTwo()
+	TooManyValues
+
+	// NotAnExpr occurs when a type expression is used where a value expression
+	// is expected.
+	//
+	// Example:
+	//  type T struct {}
+	//
+	//  func f() {
+	//  	T
+	//  }
+	NotAnExpr
+
+	/* exprs > const */
+
+	// TruncatedFloat occurs when a float constant is truncated to an integer
+	// value.
+	//
+	// Example:
+	//  var _ int = 98.6
+	TruncatedFloat
+
+	// NumericOverflow occurs when a numeric constant overflows its target type.
+	//
+	// Example:
+	//  var x int8 = 1000
+	NumericOverflow
+
+	/* exprs > operation */
+
+	// UndefinedOp occurs when an operator is not defined for the type(s) used
+	// in an operation.
+	//
+	// Example:
+	//  var c = "a" - "b"
+	UndefinedOp
+
+	// MismatchedTypes occurs when operand types are incompatible in a binary
+	// operation.
+	//
+	// Example:
+	//  var a = "hello"
+	//  var b = 1
+	//  var c = a - b
+	MismatchedTypes
+
+	// DivByZero occurs when a division operation is provable at compile
+	// time to be a division by zero.
+	//
+	// Example:
+	//  const divisor = 0
+	//  var x int = 1/divisor
+	DivByZero
+
+	// NonNumericIncDec occurs when an increment or decrement operator is
+	// applied to a non-numeric value.
+	//
+	// Example:
+	//  func f() {
+	//  	var c = "c"
+	//  	c++
+	//  }
+	NonNumericIncDec
+
+	/* exprs > ptr */
+
+	// UnaddressableOperand occurs when the & operator is applied to an
+	// unaddressable expression.
+	//
+	// Example:
+	//  var x = &1
+	UnaddressableOperand
+
+	// InvalidIndirection occurs when a non-pointer value is indirected via the
+	// '*' operator.
+	//
+	// Example:
+	//  var x int
+	//  var y = *x
+	InvalidIndirection
+
+	/* exprs > [] */
+
+	// NonIndexableOperand occurs when an index operation is applied to a value
+	// that cannot be indexed.
+	//
+	// Example:
+	//  var x = 1
+	//  var y = x[1]
+	NonIndexableOperand
+
+	// InvalidIndex occurs when an index argument is not of integer type,
+	// negative, or out-of-bounds.
+	//
+	// Example:
+	//  var s = [...]int{1,2,3}
+	//  var x = s[5]
+	//
+	// Example:
+	//  var s = []int{1,2,3}
+	//  var _ = s[-1]
+	//
+	// Example:
+	//  var s = []int{1,2,3}
+	//  var i string
+	//  var _ = s[i]
+	InvalidIndex
+
+	// SwappedSliceIndices occurs when constant indices in a slice expression
+	// are decreasing in value.
+	//
+	// Example:
+	//  var _ = []int{1,2,3}[2:1]
+	SwappedSliceIndices
+
+	/* operators > slice */
+
+	// NonSliceableOperand occurs when a slice operation is applied to a value
+	// whose type is not sliceable, or is unaddressable.
+	//
+	// Example:
+	//  var x = [...]int{1, 2, 3}[:1]
+	//
+	// Example:
+	//  var x = 1
+	//  var y = 1[:1]
+	NonSliceableOperand
+
+	// InvalidSliceExpr occurs when a three-index slice expression (a[x:y:z]) is
+	// applied to a string.
+	//
+	// Example:
+	//  var s = "hello"
+	//  var x = s[1:2:3]
+	InvalidSliceExpr
+
+	/* exprs > shift */
+
+	// InvalidShiftCount occurs when the right-hand side of a shift operation is
+	// either non-integer, negative, or too large.
+	//
+	// Example:
+	//  var (
+	//  	x string
+	//  	y int = 1 << x
+	//  )
+	InvalidShiftCount
+
+	// InvalidShiftOperand occurs when the shifted operand is not an integer.
+	//
+	// Example:
+	//  var s = "hello"
+	//  var x = s << 2
+	InvalidShiftOperand
+
+	/* exprs > chan */
+
+	// InvalidReceive occurs when there is a channel receive from a value that
+	// is either not a channel, or is a send-only channel.
+	//
+	// Example:
+	//  func f() {
+	//  	var x = 1
+	//  	<-x
+	//  }
+	InvalidReceive
+
+	// InvalidSend occurs when there is a channel send to a value that is not a
+	// channel, or is a receive-only channel.
+	//
+	// Example:
+	//  func f() {
+	//  	var x = 1
+	//  	x <- "hello!"
+	//  }
+	InvalidSend
+
+	/* exprs > literal */
+
+	// DuplicateLitKey occurs when an index is duplicated in a slice, array, or
+	// map literal.
+	//
+	// Example:
+	//  var _ = []int{0:1, 0:2}
+	//
+	// Example:
+	//  var _ = map[string]int{"a": 1, "a": 2}
+	DuplicateLitKey
+
+	// MissingLitKey occurs when a map literal is missing a key expression.
+	//
+	// Example:
+	//  var _ = map[string]int{1}
+	MissingLitKey
+
+	// InvalidLitIndex occurs when the key in a key-value element of a slice or
+	// array literal is not an integer constant.
+	//
+	// Example:
+	//  var i = 0
+	//  var x = []string{i: "world"}
+	InvalidLitIndex
+
+	// OversizeArrayLit occurs when an array literal exceeds its length.
+	//
+	// Example:
+	//  var _ = [2]int{1,2,3}
+	OversizeArrayLit
+
+	// MixedStructLit occurs when a struct literal contains a mix of positional
+	// and named elements.
+	//
+	// Example:
+	//  var _ = struct{i, j int}{i: 1, 2}
+	MixedStructLit
+
+	// InvalidStructLit occurs when a positional struct literal has an incorrect
+	// number of values.
+	//
+	// Example:
+	//  var _ = struct{i, j int}{1,2,3}
+	InvalidStructLit
+
+	// MissingLitField occurs when a struct literal refers to a field that does
+	// not exist on the struct type.
+	//
+	// Example:
+	//  var _ = struct{i int}{j: 2}
+	MissingLitField
+
+	// DuplicateLitField occurs when a struct literal contains duplicated
+	// fields.
+	//
+	// Example:
+	//  var _ = struct{i int}{i: 1, i: 2}
+	DuplicateLitField
+
+	// UnexportedLitField occurs when a positional struct literal implicitly
+	// assigns an unexported field of an imported type.
+	UnexportedLitField
+
+	// InvalidLitField occurs when a field name is not a valid identifier.
+	//
+	// Example:
+	//  var _ = struct{i int}{1: 1}
+	InvalidLitField
+
+	// UntypedLit occurs when a composite literal omits a required type
+	// identifier.
+	//
+	// Example:
+	//  type outer struct{
+	//  	inner struct { i int }
+	//  }
+	//
+	//  var _ = outer{inner: {1}}
+	UntypedLit
+
+	// InvalidLit occurs when a composite literal expression does not match its
+	// type.
+	//
+	// Example:
+	//  type P *struct{
+	//  	x int
+	//  }
+	//  var _ = P {}
+	InvalidLit
+
+	/* exprs > selector */
+
+	// AmbiguousSelector occurs when a selector is ambiguous.
+	//
+	// Example:
+	//  type E1 struct { i int }
+	//  type E2 struct { i int }
+	//  type T struct { E1; E2 }
+	//
+	//  var x T
+	//  var _ = x.i
+	AmbiguousSelector
+
+	// UndeclaredImportedName occurs when a package-qualified identifier is
+	// undeclared by the imported package.
+	//
+	// Example:
+	//  import "go/types"
+	//
+	//  var _ = types.NotAnActualIdentifier
+	UndeclaredImportedName
+
+	// UnexportedName occurs when a selector refers to an unexported identifier
+	// of an imported package.
+	//
+	// Example:
+	//  import "reflect"
+	//
+	//  type _ reflect.flag
+	UnexportedName
+
+	// UndeclaredName occurs when an identifier is not declared in the current
+	// scope.
+	//
+	// Example:
+	//  var x T
+	UndeclaredName
+
+	// MissingFieldOrMethod occurs when a selector references a field or method
+	// that does not exist.
+	//
+	// Example:
+	//  type T struct {}
+	//
+	//  var x = T{}.f
+	MissingFieldOrMethod
+
+	/* exprs > ... */
+
+	// BadDotDotDotSyntax occurs when a "..." occurs in a context where it is
+	// not valid.
+	//
+	// Example:
+	//  var _ = map[int][...]int{0: {}}
+	BadDotDotDotSyntax
+
+	// NonVariadicDotDotDot occurs when a "..." is used on the final argument to
+	// a non-variadic function.
+	//
+	// Example:
+	//  func printArgs(s []string) {
+	//  	for _, a := range s {
+	//  		println(a)
+	//  	}
+	//  }
+	//
+	//  func f() {
+	//  	s := []string{"a", "b", "c"}
+	//  	printArgs(s...)
+	//  }
+	NonVariadicDotDotDot
+
+	// MisplacedDotDotDot occurs when a "..." is used somewhere other than the
+	// final argument to a function call.
+	//
+	// Example:
+	//  func printArgs(args ...int) {
+	//  	for _, a := range args {
+	//  		println(a)
+	//  	}
+	//  }
+	//
+	//  func f() {
+	//  	a := []int{1,2,3}
+	//  	printArgs(0, a...)
+	//  }
+	MisplacedDotDotDot
+
+	// InvalidDotDotDotOperand occurs when a "..." operator is applied to a
+	// single-valued operand.
+	//
+	// Example:
+	//  func printArgs(args ...int) {
+	//  	for _, a := range args {
+	//  		println(a)
+	//  	}
+	//  }
+	//
+	//  func f() {
+	//  	a := 1
+	//  	printArgs(a...)
+	//  }
+	//
+	// Example:
+	//  func args() (int, int) {
+	//  	return 1, 2
+	//  }
+	//
+	//  func printArgs(args ...int) {
+	//  	for _, a := range args {
+	//  		println(a)
+	//  	}
+	//  }
+	//
+	//  func g() {
+	//  	printArgs(args()...)
+	//  }
+	InvalidDotDotDotOperand
+
+	// InvalidDotDotDot occurs when a "..." is used in a non-variadic built-in
+	// function.
+	//
+	// Example:
+	//  var s = []int{1, 2, 3}
+	//  var l = len(s...)
+	InvalidDotDotDot
+
+	/* exprs > built-in */
+
+	// UncalledBuiltin occurs when a built-in function is used as a
+	// function-valued expression, instead of being called.
+	//
+	// Per the spec:
+	//  "The built-in functions do not have standard Go types, so they can only
+	//  appear in call expressions; they cannot be used as function values."
+	//
+	// Example:
+	//  var _ = copy
+	UncalledBuiltin
+
+	// InvalidAppend occurs when append is called with a first argument that is
+	// not a slice.
+	//
+	// Example:
+	//  var _ = append(1, 2)
+	InvalidAppend
+
+	// InvalidCap occurs when an argument to the cap built-in function is not of
+	// supported type.
+	//
+	// See https://golang.org/ref/spec#Lengthand_capacity for information on
+	// which underlying types are supported as arguments to cap and len.
+	//
+	// Example:
+	//  var s = 2
+	//  var x = cap(s)
+	InvalidCap
+
+	// InvalidClose occurs when close(...) is called with an argument that is
+	// not of channel type, or that is a receive-only channel.
+	//
+	// Example:
+	//  func f() {
+	//  	var x int
+	//  	close(x)
+	//  }
+	InvalidClose
+
+	// InvalidCopy occurs when the arguments are not of slice type or do not
+	// have compatible type.
+	//
+	// See https://golang.org/ref/spec#Appendingand_copying_slices for more
+	// information on the type requirements for the copy built-in.
+	//
+	// Example:
+	//  func f() {
+	//  	var x []int
+	//  	y := []int64{1,2,3}
+	//  	copy(x, y)
+	//  }
+	InvalidCopy
+
+	// InvalidComplex occurs when the complex built-in function is called with
+	// arguments with incompatible types.
+	//
+	// Example:
+	//  var _ = complex(float32(1), float64(2))
+	InvalidComplex
+
+	// InvalidDelete occurs when the delete built-in function is called with a
+	// first argument that is not a map.
+	//
+	// Example:
+	//  func f() {
+	//  	m := "hello"
+	//  	delete(m, "e")
+	//  }
+	InvalidDelete
+
+	// InvalidImag occurs when the imag built-in function is called with an
+	// argument that does not have complex type.
+	//
+	// Example:
+	//  var _ = imag(int(1))
+	InvalidImag
+
+	// InvalidLen occurs when an argument to the len built-in function is not of
+	// supported type.
+	//
+	// See https://golang.org/ref/spec#Lengthand_capacity for information on
+	// which underlying types are supported as arguments to cap and len.
+	//
+	// Example:
+	//  var s = 2
+	//  var x = len(s)
+	InvalidLen
+
+	// SwappedMakeArgs occurs when make is called with three arguments, and its
+	// length argument is larger than its capacity argument.
+	//
+	// Example:
+	//  var x = make([]int, 3, 2)
+	SwappedMakeArgs
+
+	// InvalidMake occurs when make is called with an unsupported type argument.
+	//
+	// See https://golang.org/ref/spec#Makingslices_maps_and_channels for
+	// information on the types that may be created using make.
+	//
+	// Example:
+	//  var x = make(int)
+	InvalidMake
+
+	// InvalidReal occurs when the real built-in function is called with an
+	// argument that does not have complex type.
+	//
+	// Example:
+	//  var _ = real(int(1))
+	InvalidReal
+
+	/* exprs > assertion */
+
+	// InvalidAssert occurs when a type assertion is applied to a
+	// value that is not of interface type.
+	//
+	// Example:
+	//  var x = 1
+	//  var _ = x.(float64)
+	InvalidAssert
+
+	// ImpossibleAssert occurs for a type assertion x.(T) when the value x of
+	// interface cannot have dynamic type T, due to a missing or mismatching
+	// method on T.
+	//
+	// Example:
+	//  type T int
+	//
+	//  func (t *T) m() int { return int(*t) }
+	//
+	//  type I interface { m() int }
+	//
+	//  var x I
+	//  var _ = x.(T)
+	ImpossibleAssert
+
+	/* exprs > conversion */
+
+	// InvalidConversion occurs when the argument type cannot be converted to the
+	// target.
+	//
+	// See https://golang.org/ref/spec#Conversions for the rules of
+	// convertibility.
+	//
+	// Example:
+	//  var x float64
+	//  var _ = string(x)
+	InvalidConversion
+
+	// InvalidUntypedConversion occurs when an there is no valid implicit
+	// conversion from an untyped value satisfying the type constraints of the
+	// context in which it is used.
+	//
+	// Example:
+	//  var _ = 1 + ""
+	InvalidUntypedConversion
+
+	/* offsetof */
+
+	// BadOffsetofSyntax occurs when unsafe.Offsetof is called with an argument
+	// that is not a selector expression.
+	//
+	// Example:
+	//  import "unsafe"
+	//
+	//  var x int
+	//  var _ = unsafe.Offsetof(x)
+	BadOffsetofSyntax
+
+	// InvalidOffsetof occurs when unsafe.Offsetof is called with a method
+	// selector, rather than a field selector, or when the field is embedded via
+	// a pointer.
+	//
+	// Per the spec:
+	//
+	//  "If f is an embedded field, it must be reachable without pointer
+	//  indirections through fields of the struct. "
+	//
+	// Example:
+	//  import "unsafe"
+	//
+	//  type T struct { f int }
+	//  type S struct { *T }
+	//  var s S
+	//  var _ = unsafe.Offsetof(s.f)
+	//
+	// Example:
+	//  import "unsafe"
+	//
+	//  type S struct{}
+	//
+	//  func (S) m() {}
+	//
+	//  var s S
+	//  var _ = unsafe.Offsetof(s.m)
+	InvalidOffsetof
+
+	/* control flow > scope */
+
+	// UnusedExpr occurs when a side-effect free expression is used as a
+	// statement. Such a statement has no effect.
+	//
+	// Example:
+	//  func f(i int) {
+	//  	i*i
+	//  }
+	UnusedExpr
+
+	// UnusedVar occurs when a variable is declared but unused.
+	//
+	// Example:
+	//  func f() {
+	//  	x := 1
+	//  }
+	UnusedVar
+
+	// MissingReturn occurs when a function with results is missing a return
+	// statement.
+	//
+	// Example:
+	//  func f() int {}
+	MissingReturn
+
+	// WrongResultCount occurs when a return statement returns an incorrect
+	// number of values.
+	//
+	// Example:
+	//  func ReturnOne() int {
+	//  	return 1, 2
+	//  }
+	WrongResultCount
+
+	// OutOfScopeResult occurs when the name of a value implicitly returned by
+	// an empty return statement is shadowed in a nested scope.
+	//
+	// Example:
+	//  func factor(n int) (i int) {
+	//  	for i := 2; i < n; i++ {
+	//  		if n%i == 0 {
+	//  			return
+	//  		}
+	//  	}
+	//  	return 0
+	//  }
+	OutOfScopeResult
+
+	/* control flow > if */
+
+	// InvalidCond occurs when an if condition is not a boolean expression.
+	//
+	// Example:
+	//  func checkReturn(i int) {
+	//  	if i {
+	//  		panic("non-zero return")
+	//  	}
+	//  }
+	InvalidCond
+
+	/* control flow > for */
+
+	// InvalidPostDecl occurs when there is a declaration in a for-loop post
+	// statement.
+	//
+	// Example:
+	//  func f() {
+	//  	for i := 0; i < 10; j := 0 {}
+	//  }
+	InvalidPostDecl
+
+	// InvalidChanRange occurs when a send-only channel used in a range
+	// expression.
+	//
+	// Example:
+	//  func sum(c chan<- int) {
+	//  	s := 0
+	//  	for i := range c {
+	//  		s += i
+	//  	}
+	//  }
+	InvalidChanRange
+
+	// InvalidIterVar occurs when two iteration variables are used while ranging
+	// over a channel.
+	//
+	// Example:
+	//  func f(c chan int) {
+	//  	for k, v := range c {
+	//  		println(k, v)
+	//  	}
+	//  }
+	InvalidIterVar
+
+	// InvalidRangeExpr occurs when the type of a range expression is not array,
+	// slice, string, map, or channel.
+	//
+	// Example:
+	//  func f(i int) {
+	//  	for j := range i {
+	//  		println(j)
+	//  	}
+	//  }
+	InvalidRangeExpr
+
+	/* control flow > switch */
+
+	// MisplacedBreak occurs when a break statement is not within a for, switch,
+	// or select statement of the innermost function definition.
+	//
+	// Example:
+	//  func f() {
+	//  	break
+	//  }
+	MisplacedBreak
+
+	// MisplacedContinue occurs when a continue statement is not within a for
+	// loop of the innermost function definition.
+	//
+	// Example:
+	//  func sumeven(n int) int {
+	//  	proceed := func() {
+	//  		continue
+	//  	}
+	//  	sum := 0
+	//  	for i := 1; i <= n; i++ {
+	//  		if i % 2 != 0 {
+	//  			proceed()
+	//  		}
+	//  		sum += i
+	//  	}
+	//  	return sum
+	//  }
+	MisplacedContinue
+
+	// MisplacedFallthrough occurs when a fallthrough statement is not within an
+	// expression switch.
+	//
+	// Example:
+	//  func typename(i interface{}) string {
+	//  	switch i.(type) {
+	//  	case int64:
+	//  		fallthrough
+	//  	case int:
+	//  		return "int"
+	//  	}
+	//  	return "unsupported"
+	//  }
+	MisplacedFallthrough
+
+	// DuplicateCase occurs when a type or expression switch has duplicate
+	// cases.
+	//
+	// Example:
+	//  func printInt(i int) {
+	//  	switch i {
+	//  	case 1:
+	//  		println("one")
+	//  	case 1:
+	//  		println("One")
+	//  	}
+	//  }
+	DuplicateCase
+
+	// DuplicateDefault occurs when a type or expression switch has multiple
+	// default clauses.
+	//
+	// Example:
+	//  func printInt(i int) {
+	//  	switch i {
+	//  	case 1:
+	//  		println("one")
+	//  	default:
+	//  		println("One")
+	//  	default:
+	//  		println("1")
+	//  	}
+	//  }
+	DuplicateDefault
+
+	// BadTypeKeyword occurs when a .(type) expression is used anywhere other
+	// than a type switch.
+	//
+	// Example:
+	//  type I interface {
+	//  	m()
+	//  }
+	//  var t I
+	//  var _ = t.(type)
+	BadTypeKeyword
+
+	// InvalidTypeSwitch occurs when .(type) is used on an expression that is
+	// not of interface type.
+	//
+	// Example:
+	//  func f(i int) {
+	//  	switch x := i.(type) {}
+	//  }
+	InvalidTypeSwitch
+
+	// InvalidExprSwitch occurs when a switch expression is not comparable.
+	//
+	// Example:
+	//  func _() {
+	//  	var a struct{ _ func() }
+	//  	switch a /* ERROR cannot switch on a */ {
+	//  	}
+	//  }
+	InvalidExprSwitch
+
+	/* control flow > select */
+
+	// InvalidSelectCase occurs when a select case is not a channel send or
+	// receive.
+	//
+	// Example:
+	//  func checkChan(c <-chan int) bool {
+	//  	select {
+	//  	case c:
+	//  		return true
+	//  	default:
+	//  		return false
+	//  	}
+	//  }
+	InvalidSelectCase
+
+	/* control flow > labels and jumps */
+
+	// UndeclaredLabel occurs when an undeclared label is jumped to.
+	//
+	// Example:
+	//  func f() {
+	//  	goto L
+	//  }
+	UndeclaredLabel
+
+	// DuplicateLabel occurs when a label is declared more than once.
+	//
+	// Example:
+	//  func f() int {
+	//  L:
+	//  L:
+	//  	return 1
+	//  }
+	DuplicateLabel
+
+	// MisplacedLabel occurs when a break or continue label is not on a for,
+	// switch, or select statement.
+	//
+	// Example:
+	//  func f() {
+	//  L:
+	//  	a := []int{1,2,3}
+	//  	for _, e := range a {
+	//  		if e > 10 {
+	//  			break L
+	//  		}
+	//  		println(a)
+	//  	}
+	//  }
+	MisplacedLabel
+
+	// UnusedLabel occurs when a label is declared but not used.
+	//
+	// Example:
+	//  func f() {
+	//  L:
+	//  }
+	UnusedLabel
+
+	// JumpOverDecl occurs when a label jumps over a variable declaration.
+	//
+	// Example:
+	//  func f() int {
+	//  	goto L
+	//  	x := 2
+	//  L:
+	//  	x++
+	//  	return x
+	//  }
+	JumpOverDecl
+
+	// JumpIntoBlock occurs when a forward jump goes to a label inside a nested
+	// block.
+	//
+	// Example:
+	//  func f(x int) {
+	//  	goto L
+	//  	if x > 0 {
+	//  	L:
+	//  		print("inside block")
+	//  	}
+	// }
+	JumpIntoBlock
+
+	/* control flow > calls */
+
+	// InvalidMethodExpr occurs when a pointer method is called but the argument
+	// is not addressable.
+	//
+	// Example:
+	//  type T struct {}
+	//
+	//  func (*T) m() int { return 1 }
+	//
+	//  var _ = T.m(T{})
+	InvalidMethodExpr
+
+	// WrongArgCount occurs when too few or too many arguments are passed by a
+	// function call.
+	//
+	// Example:
+	//  func f(i int) {}
+	//  var x = f()
+	WrongArgCount
+
+	// InvalidCall occurs when an expression is called that is not of function
+	// type.
+	//
+	// Example:
+	//  var x = "x"
+	//  var y = x()
+	InvalidCall
+
+	/* control flow > suspended */
+
+	// UnusedResults occurs when a restricted expression-only built-in function
+	// is suspended via go or defer. Such a suspension discards the results of
+	// these side-effect free built-in functions, and therefore is ineffectual.
+	//
+	// Example:
+	//  func f(a []int) int {
+	//  	defer len(a)
+	//  	return i
+	//  }
+	UnusedResults
+
+	// InvalidDefer occurs when a deferred expression is not a function call,
+	// for example if the expression is a type conversion.
+	//
+	// Example:
+	//  func f(i int) int {
+	//  	defer int32(i)
+	//  	return i
+	//  }
+	InvalidDefer
+
+	// InvalidGo occurs when a go expression is not a function call, for example
+	// if the expression is a type conversion.
+	//
+	// Example:
+	//  func f(i int) int {
+	//  	go int32(i)
+	//  	return i
+	//  }
+	InvalidGo
+)
diff --git a/vendor/golang.org/x/tools/internal/typesinternal/errorcode_string.go b/vendor/golang.org/x/tools/internal/typesinternal/errorcode_string.go
new file mode 100644
index 0000000..3e5842a
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/typesinternal/errorcode_string.go
@@ -0,0 +1,153 @@
+// Code generated by "stringer -type=ErrorCode"; DO NOT EDIT.
+
+package typesinternal
+
+import "strconv"
+
+func _() {
+	// An "invalid array index" compiler error signifies that the constant values have changed.
+	// Re-run the stringer command to generate them again.
+	var x [1]struct{}
+	_ = x[Test-1]
+	_ = x[BlankPkgName-2]
+	_ = x[MismatchedPkgName-3]
+	_ = x[InvalidPkgUse-4]
+	_ = x[BadImportPath-5]
+	_ = x[BrokenImport-6]
+	_ = x[ImportCRenamed-7]
+	_ = x[UnusedImport-8]
+	_ = x[InvalidInitCycle-9]
+	_ = x[DuplicateDecl-10]
+	_ = x[InvalidDeclCycle-11]
+	_ = x[InvalidTypeCycle-12]
+	_ = x[InvalidConstInit-13]
+	_ = x[InvalidConstVal-14]
+	_ = x[InvalidConstType-15]
+	_ = x[UntypedNil-16]
+	_ = x[WrongAssignCount-17]
+	_ = x[UnassignableOperand-18]
+	_ = x[NoNewVar-19]
+	_ = x[MultiValAssignOp-20]
+	_ = x[InvalidIfaceAssign-21]
+	_ = x[InvalidChanAssign-22]
+	_ = x[IncompatibleAssign-23]
+	_ = x[UnaddressableFieldAssign-24]
+	_ = x[NotAType-25]
+	_ = x[InvalidArrayLen-26]
+	_ = x[BlankIfaceMethod-27]
+	_ = x[IncomparableMapKey-28]
+	_ = x[InvalidIfaceEmbed-29]
+	_ = x[InvalidPtrEmbed-30]
+	_ = x[BadRecv-31]
+	_ = x[InvalidRecv-32]
+	_ = x[DuplicateFieldAndMethod-33]
+	_ = x[DuplicateMethod-34]
+	_ = x[InvalidBlank-35]
+	_ = x[InvalidIota-36]
+	_ = x[MissingInitBody-37]
+	_ = x[InvalidInitSig-38]
+	_ = x[InvalidInitDecl-39]
+	_ = x[InvalidMainDecl-40]
+	_ = x[TooManyValues-41]
+	_ = x[NotAnExpr-42]
+	_ = x[TruncatedFloat-43]
+	_ = x[NumericOverflow-44]
+	_ = x[UndefinedOp-45]
+	_ = x[MismatchedTypes-46]
+	_ = x[DivByZero-47]
+	_ = x[NonNumericIncDec-48]
+	_ = x[UnaddressableOperand-49]
+	_ = x[InvalidIndirection-50]
+	_ = x[NonIndexableOperand-51]
+	_ = x[InvalidIndex-52]
+	_ = x[SwappedSliceIndices-53]
+	_ = x[NonSliceableOperand-54]
+	_ = x[InvalidSliceExpr-55]
+	_ = x[InvalidShiftCount-56]
+	_ = x[InvalidShiftOperand-57]
+	_ = x[InvalidReceive-58]
+	_ = x[InvalidSend-59]
+	_ = x[DuplicateLitKey-60]
+	_ = x[MissingLitKey-61]
+	_ = x[InvalidLitIndex-62]
+	_ = x[OversizeArrayLit-63]
+	_ = x[MixedStructLit-64]
+	_ = x[InvalidStructLit-65]
+	_ = x[MissingLitField-66]
+	_ = x[DuplicateLitField-67]
+	_ = x[UnexportedLitField-68]
+	_ = x[InvalidLitField-69]
+	_ = x[UntypedLit-70]
+	_ = x[InvalidLit-71]
+	_ = x[AmbiguousSelector-72]
+	_ = x[UndeclaredImportedName-73]
+	_ = x[UnexportedName-74]
+	_ = x[UndeclaredName-75]
+	_ = x[MissingFieldOrMethod-76]
+	_ = x[BadDotDotDotSyntax-77]
+	_ = x[NonVariadicDotDotDot-78]
+	_ = x[MisplacedDotDotDot-79]
+	_ = x[InvalidDotDotDotOperand-80]
+	_ = x[InvalidDotDotDot-81]
+	_ = x[UncalledBuiltin-82]
+	_ = x[InvalidAppend-83]
+	_ = x[InvalidCap-84]
+	_ = x[InvalidClose-85]
+	_ = x[InvalidCopy-86]
+	_ = x[InvalidComplex-87]
+	_ = x[InvalidDelete-88]
+	_ = x[InvalidImag-89]
+	_ = x[InvalidLen-90]
+	_ = x[SwappedMakeArgs-91]
+	_ = x[InvalidMake-92]
+	_ = x[InvalidReal-93]
+	_ = x[InvalidAssert-94]
+	_ = x[ImpossibleAssert-95]
+	_ = x[InvalidConversion-96]
+	_ = x[InvalidUntypedConversion-97]
+	_ = x[BadOffsetofSyntax-98]
+	_ = x[InvalidOffsetof-99]
+	_ = x[UnusedExpr-100]
+	_ = x[UnusedVar-101]
+	_ = x[MissingReturn-102]
+	_ = x[WrongResultCount-103]
+	_ = x[OutOfScopeResult-104]
+	_ = x[InvalidCond-105]
+	_ = x[InvalidPostDecl-106]
+	_ = x[InvalidChanRange-107]
+	_ = x[InvalidIterVar-108]
+	_ = x[InvalidRangeExpr-109]
+	_ = x[MisplacedBreak-110]
+	_ = x[MisplacedContinue-111]
+	_ = x[MisplacedFallthrough-112]
+	_ = x[DuplicateCase-113]
+	_ = x[DuplicateDefault-114]
+	_ = x[BadTypeKeyword-115]
+	_ = x[InvalidTypeSwitch-116]
+	_ = x[InvalidExprSwitch-117]
+	_ = x[InvalidSelectCase-118]
+	_ = x[UndeclaredLabel-119]
+	_ = x[DuplicateLabel-120]
+	_ = x[MisplacedLabel-121]
+	_ = x[UnusedLabel-122]
+	_ = x[JumpOverDecl-123]
+	_ = x[JumpIntoBlock-124]
+	_ = x[InvalidMethodExpr-125]
+	_ = x[WrongArgCount-126]
+	_ = x[InvalidCall-127]
+	_ = x[UnusedResults-128]
+	_ = x[InvalidDefer-129]
+	_ = x[InvalidGo-130]
+}
+
+const _ErrorCode_name = "TestBlankPkgNameMismatchedPkgNameInvalidPkgUseBadImportPathBrokenImportImportCRenamedUnusedImportInvalidInitCycleDuplicateDeclInvalidDeclCycleInvalidTypeCycleInvalidConstInitInvalidConstValInvalidConstTypeUntypedNilWrongAssignCountUnassignableOperandNoNewVarMultiValAssignOpInvalidIfaceAssignInvalidChanAssignIncompatibleAssignUnaddressableFieldAssignNotATypeInvalidArrayLenBlankIfaceMethodIncomparableMapKeyInvalidIfaceEmbedInvalidPtrEmbedBadRecvInvalidRecvDuplicateFieldAndMethodDuplicateMethodInvalidBlankInvalidIotaMissingInitBodyInvalidInitSigInvalidInitDeclInvalidMainDeclTooManyValuesNotAnExprTruncatedFloatNumericOverflowUndefinedOpMismatchedTypesDivByZeroNonNumericIncDecUnaddressableOperandInvalidIndirectionNonIndexableOperandInvalidIndexSwappedSliceIndicesNonSliceableOperandInvalidSliceExprInvalidShiftCountInvalidShiftOperandInvalidReceiveInvalidSendDuplicateLitKeyMissingLitKeyInvalidLitIndexOversizeArrayLitMixedStructLitInvalidStructLitMissingLitFieldDuplicateLitFieldUnexportedLitFieldInvalidLitFieldUntypedLitInvalidLitAmbiguousSelectorUndeclaredImportedNameUnexportedNameUndeclaredNameMissingFieldOrMethodBadDotDotDotSyntaxNonVariadicDotDotDotMisplacedDotDotDotInvalidDotDotDotOperandInvalidDotDotDotUncalledBuiltinInvalidAppendInvalidCapInvalidCloseInvalidCopyInvalidComplexInvalidDeleteInvalidImagInvalidLenSwappedMakeArgsInvalidMakeInvalidRealInvalidAssertImpossibleAssertInvalidConversionInvalidUntypedConversionBadOffsetofSyntaxInvalidOffsetofUnusedExprUnusedVarMissingReturnWrongResultCountOutOfScopeResultInvalidCondInvalidPostDeclInvalidChanRangeInvalidIterVarInvalidRangeExprMisplacedBreakMisplacedContinueMisplacedFallthroughDuplicateCaseDuplicateDefaultBadTypeKeywordInvalidTypeSwitchInvalidExprSwitchInvalidSelectCaseUndeclaredLabelDuplicateLabelMisplacedLabelUnusedLabelJumpOverDeclJumpIntoBlockInvalidMethodExprWrongArgCountInvalidCallUnusedResultsInvalidDeferInvalidGo"
+
+var _ErrorCode_index = [...]uint16{0, 4, 16, 33, 46, 59, 71, 85, 97, 113, 126, 142, 158, 174, 189, 205, 215, 231, 250, 258, 274, 292, 309, 327, 351, 359, 374, 390, 408, 425, 440, 447, 458, 481, 496, 508, 519, 534, 548, 563, 578, 591, 600, 614, 629, 640, 655, 664, 680, 700, 718, 737, 749, 768, 787, 803, 820, 839, 853, 864, 879, 892, 907, 923, 937, 953, 968, 985, 1003, 1018, 1028, 1038, 1055, 1077, 1091, 1105, 1125, 1143, 1163, 1181, 1204, 1220, 1235, 1248, 1258, 1270, 1281, 1295, 1308, 1319, 1329, 1344, 1355, 1366, 1379, 1395, 1412, 1436, 1453, 1468, 1478, 1487, 1500, 1516, 1532, 1543, 1558, 1574, 1588, 1604, 1618, 1635, 1655, 1668, 1684, 1698, 1715, 1732, 1749, 1764, 1778, 1792, 1803, 1815, 1828, 1845, 1858, 1869, 1882, 1894, 1903}
+
+func (i ErrorCode) String() string {
+	i -= 1
+	if i < 0 || i >= ErrorCode(len(_ErrorCode_index)-1) {
+		return "ErrorCode(" + strconv.FormatInt(int64(i+1), 10) + ")"
+	}
+	return _ErrorCode_name[_ErrorCode_index[i]:_ErrorCode_index[i+1]]
+}
diff --git a/vendor/golang.org/x/tools/internal/typesinternal/types.go b/vendor/golang.org/x/tools/internal/typesinternal/types.go
new file mode 100644
index 0000000..7c77c2f
--- /dev/null
+++ b/vendor/golang.org/x/tools/internal/typesinternal/types.go
@@ -0,0 +1,50 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package typesinternal provides access to internal go/types APIs that are not
+// yet exported.
+package typesinternal
+
+import (
+	"go/token"
+	"go/types"
+	"reflect"
+	"unsafe"
+)
+
+func SetUsesCgo(conf *types.Config) bool {
+	v := reflect.ValueOf(conf).Elem()
+
+	f := v.FieldByName("go115UsesCgo")
+	if !f.IsValid() {
+		f = v.FieldByName("UsesCgo")
+		if !f.IsValid() {
+			return false
+		}
+	}
+
+	addr := unsafe.Pointer(f.UnsafeAddr())
+	*(*bool)(addr) = true
+
+	return true
+}
+
+// ReadGo116ErrorData extracts additional information from types.Error values
+// generated by Go version 1.16 and later: the error code, start position, and
+// end position. If all positions are valid, start <= err.Pos <= end.
+//
+// If the data could not be read, the final result parameter will be false.
+func ReadGo116ErrorData(err types.Error) (code ErrorCode, start, end token.Pos, ok bool) {
+	var data [3]int
+	// By coincidence all of these fields are ints, which simplifies things.
+	v := reflect.ValueOf(err)
+	for i, name := range []string{"go116code", "go116start", "go116end"} {
+		f := v.FieldByName(name)
+		if !f.IsValid() {
+			return 0, 0, 0, false
+		}
+		data[i] = int(f.Int())
+	}
+	return ErrorCode(data[0]), token.Pos(data[1]), token.Pos(data[2]), true
+}