Added off thread compilation

Co-authored-by: Gregory Terzian <2792687+gterzian@users.noreply.github.com>
Co-authored-by: Abhishek Sharma <20724848+AbhishekSharma102@users.noreply.github.com>

8 files changed, 315 insertions, 90 deletions

diff --git a/components/config/prefs.rs b/components/config/prefs.rs
index 5ac6b19d940..db889d419ee 100644
--- a/components/config/prefs.rs
+++ b/components/config/prefs.rs
@@ -186,6 +186,9 @@ mod gen {
                         allowed_in_nonsecure_contexts: bool,
                     }
                 },
+                script: {
+                    asynch: bool,
+                },
                 serviceworker: {
                     enabled: bool,
                     timeout_seconds: i64,
diff --git a/components/script/devtools.rs b/components/script/devtools.rs
index cb5dfa27b7f..04c35755b89 100644
--- a/components/script/devtools.rs
+++ b/components/script/devtools.rs
@@ -14,6 +14,7 @@ use crate::dom::bindings::str::DOMString;
 use crate::dom::document::AnimationFrameCallback;
 use crate::dom::element::Element;
 use crate::dom::globalscope::GlobalScope;
+use crate::dom::htmlscriptelement::SourceCode;
 use crate::dom::node::{window_from_node, Node, ShadowIncluding};
 use crate::realms::enter_realm;
 use crate::script_module::ScriptFetchOptions;
@@ -25,6 +26,7 @@ use js::jsval::UndefinedValue;
 use js::rust::wrappers::ObjectClassName;
 use msg::constellation_msg::PipelineId;
 use std::ffi::CStr;
+use std::rc::Rc;
 use std::str;
 use uuid::Uuid;
 
@@ -35,8 +37,9 @@ pub fn handle_evaluate_js(global: &GlobalScope, eval: String, reply: IpcSender<E
         let cx = global.get_cx();
         let _ac = enter_realm(global);
         rooted!(in(*cx) let mut rval = UndefinedValue());
+        let source_code = SourceCode::Text(Rc::new(DOMString::from_string(eval)));
         global.evaluate_script_on_global_with_result(
-            &eval,
+            &source_code,
             "<eval>",
             rval.handle_mut(),
             1,
diff --git a/components/script/dom/bindings/trace.rs b/components/script/dom/bindings/trace.rs
index 92d6ebcb7bf..a752b129a12 100644
--- a/components/script/dom/bindings/trace.rs
+++ b/components/script/dom/bindings/trace.rs
@@ -77,8 +77,10 @@ use hyper::Method;
 use hyper::StatusCode;
 use indexmap::IndexMap;
 use ipc_channel::ipc::{IpcReceiver, IpcSender};
-use js::glue::{CallObjectTracer, CallStringTracer, CallValueTracer};
-use js::jsapi::{GCTraceKindToAscii, Heap, JSObject, JSString, JSTracer, JobQueue, TraceKind};
+use js::glue::{CallObjectTracer, CallScriptTracer, CallStringTracer, CallValueTracer};
+use js::jsapi::{
+    GCTraceKindToAscii, Heap, JSObject, JSScript, JSString, JSTracer, JobQueue, TraceKind,
+};
 use js::jsval::JSVal;
 use js::rust::{GCMethods, Handle, Runtime};
 use js::typedarray::TypedArray;
@@ -219,6 +221,18 @@ unsafe_no_jsmanaged_fields!(Cow<'static, str>);
 
 unsafe_no_jsmanaged_fields!(CspList);
 
+/// Trace a `JSScript`.
+pub fn trace_script(tracer: *mut JSTracer, description: &str, script: &Heap<*mut JSScript>) {
+    unsafe {
+        trace!("tracing {}", description);
+        CallScriptTracer(
+            tracer,
+            script.ptr.get() as *mut _,
+            GCTraceKindToAscii(TraceKind::Script),
+        );
+    }
+}
+
 /// Trace a `JSVal`.
 pub fn trace_jsval(tracer: *mut JSTracer, description: &str, val: &Heap<JSVal>) {
     unsafe {
@@ -328,6 +342,15 @@ unsafe impl<T: JSTraceable> JSTraceable for RefCell<T> {
     }
 }
 
+unsafe impl JSTraceable for Heap<*mut JSScript> {
+    unsafe fn trace(&self, trc: *mut JSTracer) {
+        if self.get().is_null() {
+            return;
+        }
+        trace_script(trc, "heap script", self);
+    }
+}
+
 unsafe impl JSTraceable for Heap<*mut JSObject> {
     unsafe fn trace(&self, trc: *mut JSTracer) {
         if self.get().is_null() {
diff --git a/components/script/dom/globalscope.rs b/components/script/dom/globalscope.rs
index a6427224882..9917d602ab3 100644
--- a/components/script/dom/globalscope.rs
+++ b/components/script/dom/globalscope.rs
@@ -38,7 +38,7 @@ use crate::dom::file::File;
 use crate::dom::gpudevice::GPUDevice;
 use crate::dom::gpuoutofmemoryerror::GPUOutOfMemoryError;
 use crate::dom::gpuvalidationerror::GPUValidationError;
-use crate::dom::htmlscriptelement::ScriptId;
+use crate::dom::htmlscriptelement::{ScriptId, SourceCode};
 use crate::dom::identityhub::Identities;
 use crate::dom::imagebitmap::ImageBitmap;
 use crate::dom::messageevent::MessageEvent;
@@ -91,9 +91,9 @@ use js::jsval::PrivateValue;
 use js::jsval::{JSVal, UndefinedValue};
 use js::panic::maybe_resume_unwind;
 use js::rust::transform_str_to_source_text;
-use js::rust::wrappers::{JS_ExecuteScript, JS_GetScriptPrivate};
+use js::rust::wrappers::{JS_ExecuteScript, JS_ExecuteScript1, JS_GetScriptPrivate};
 use js::rust::{get_object_class, CompileOptionsWrapper, ParentRuntime, Runtime};
-use js::rust::{HandleValue, MutableHandleValue};
+use js::rust::{HandleScript, HandleValue, MutableHandleValue};
 use js::{JSCLASS_IS_DOMJSCLASS, JSCLASS_IS_GLOBAL};
 use msg::constellation_msg::{
     BlobId, BroadcastChannelRouterId, MessagePortId, MessagePortRouterId, PipelineId,
@@ -2552,8 +2552,9 @@ impl GlobalScope {
         fetch_options: ScriptFetchOptions,
         script_base_url: ServoUrl,
     ) -> bool {
+        let source_code = SourceCode::Text(Rc::new(DOMString::from_string((*code).to_string())));
         self.evaluate_script_on_global_with_result(
-            code,
+            &source_code,
             "",
             rval,
             1,
@@ -2566,7 +2567,7 @@ impl GlobalScope {
     #[allow(unsafe_code)]
     pub fn evaluate_script_on_global_with_result(
         &self,
-        code: &str,
+        code: &SourceCode,
         filename: &str,
         rval: MutableHandleValue,
         line_number: u32,
@@ -2595,48 +2596,58 @@ impl GlobalScope {
                 let _aes = AutoEntryScript::new(self);
 
                 unsafe {
-                    let options = CompileOptionsWrapper::new(*cx, filename.as_ptr(), line_number);
-
-                    debug!("compiling Dom string");
-                    rooted!(in(*cx) let compiled_script =
-                        Compile1(
-                            *cx,
-                            options.ptr,
-                            &mut transform_str_to_source_text(code),
-                        )
-                    );
+                    let result = match code {
+                        SourceCode::Text(text_code) => {
+                            let options =
+                                CompileOptionsWrapper::new(*cx, filename.as_ptr(), line_number);
+
+                            debug!("compiling Dom string");
+                            rooted!(in(*cx) let compiled_script =
+                                Compile1(
+                                    *cx,
+                                    options.ptr,
+                                    &mut transform_str_to_source_text(text_code),
+                                )
+                            );
 
-                    if compiled_script.is_null() {
-                        debug!("error compiling Dom string");
-                        report_pending_exception(*cx, true, InRealm::Entered(&ar));
-                        return false;
-                    }
+                            if compiled_script.is_null() {
+                                debug!("error compiling Dom string");
+                                report_pending_exception(*cx, true, InRealm::Entered(&ar));
+                                return false;
+                            }
 
-                    rooted!(in(*cx) let mut script_private = UndefinedValue());
-                    JS_GetScriptPrivate(*compiled_script, script_private.handle_mut());
-
-                    // When `ScriptPrivate` for the compiled script is undefined,
-                    // we need to set it so that it can be used in dynamic import context.
-                    if script_private.is_undefined() {
-                        debug!("Set script private for {}", script_base_url);
-
-                        let module_script_data = Rc::new(ModuleScript::new(
-                            script_base_url,
-                            fetch_options,
-                            // We can't initialize an module owner here because
-                            // the executing context of script might be different
-                            // from the dynamic import script's executing context.
-                            None,
-                        ));
-
-                        SetScriptPrivate(
-                            *compiled_script,
-                            &PrivateValue(Rc::into_raw(module_script_data) as *const _),
-                        );
-                    }
+                            rooted!(in(*cx) let mut script_private = UndefinedValue());
+                            JS_GetScriptPrivate(*compiled_script, script_private.handle_mut());
+
+                            // When `ScriptPrivate` for the compiled script is undefined,
+                            // we need to set it so that it can be used in dynamic import context.
+                            if script_private.is_undefined() {
+                                debug!("Set script private for {}", script_base_url);
+
+                                let module_script_data = Rc::new(ModuleScript::new(
+                                    script_base_url,
+                                    fetch_options,
+                                    // We can't initialize an module owner here because
+                                    // the executing context of script might be different
+                                    // from the dynamic import script's executing context.
+                                    None,
+                                ));
+
+                                SetScriptPrivate(
+                                    *compiled_script,
+                                    &PrivateValue(Rc::into_raw(module_script_data) as *const _),
+                                );
+                            }
 
-                    debug!("evaluating Dom string");
-                    let result = JS_ExecuteScript(*cx, compiled_script.handle(), rval);
+                            debug!("evaluating Dom string");
+                            JS_ExecuteScript(*cx, compiled_script.handle(), rval)
+                        },
+                        SourceCode::Compiled(compiled_script) => {
+                            let script = compiled_script.source_code.get();
+                            let script_handle = HandleScript::new(&script);
+                            JS_ExecuteScript1(*cx, script_handle)
+                        },
+                    };
 
                     if !result {
                         debug!("error evaluating Dom string");
diff --git a/components/script/dom/htmlscriptelement.rs b/components/script/dom/htmlscriptelement.rs
index 2ad7444f7f4..baa22d4dfe6 100644
--- a/components/script/dom/htmlscriptelement.rs
+++ b/components/script/dom/htmlscriptelement.rs
@@ -13,6 +13,7 @@ use crate::dom::bindings::reflector::DomObject;
 use crate::dom::bindings::root::{Dom, DomRoot};
 use crate::dom::bindings::settings_stack::AutoEntryScript;
 use crate::dom::bindings::str::{DOMString, USVString};
+use crate::dom::bindings::trace::RootedTraceableBox;
 use crate::dom::document::Document;
 use crate::dom::element::{
     cors_setting_for_element, reflect_cross_origin_attribute, set_cross_origin_attribute,
@@ -27,15 +28,25 @@ use crate::dom::performanceresourcetiming::InitiatorType;
 use crate::dom::virtualmethods::VirtualMethods;
 use crate::fetch::create_a_potential_cors_request;
 use crate::network_listener::{self, NetworkListener, PreInvoke, ResourceTimingListener};
+use crate::realms::enter_realm;
 use crate::script_module::fetch_inline_module_script;
 use crate::script_module::{fetch_external_module_script, ModuleOwner, ScriptFetchOptions};
+use crate::task::TaskCanceller;
+use crate::task_source::dom_manipulation::DOMManipulationTaskSource;
+use crate::task_source::TaskSource;
+use crate::task_source::TaskSourceName;
 use content_security_policy as csp;
+use core::ffi::c_void;
 use dom_struct::dom_struct;
 use encoding_rs::Encoding;
 use html5ever::{LocalName, Prefix};
 use ipc_channel::ipc;
 use ipc_channel::router::ROUTER;
+use js::jsapi::{
+    CanCompileOffThread, CompileOffThread, FinishOffThreadScript, Heap, JSScript, OffThreadToken,
+};
 use js::jsval::UndefinedValue;
+use js::rust::{transform_u16_to_source_text, CompileOptionsWrapper};
 use msg::constellation_msg::PipelineId;
 use net_traits::request::{
     CorsSettings, CredentialsMode, Destination, ParserMetadata, RequestBuilder,
@@ -43,11 +54,13 @@ use net_traits::request::{
 use net_traits::{FetchMetadata, FetchResponseListener, Metadata, NetworkError};
 use net_traits::{ResourceFetchTiming, ResourceTimingType};
 use servo_atoms::Atom;
+use servo_config::pref;
 use servo_url::ImmutableOrigin;
 use servo_url::ServoUrl;
 use std::cell::Cell;
 use std::fs::{create_dir_all, read_to_string, File};
 use std::io::{Read, Seek, Write};
+use std::mem::replace;
 use std::path::PathBuf;
 use std::process::Command;
 use std::rc::Rc;
@@ -55,6 +68,82 @@ use std::sync::{Arc, Mutex};
 use style::str::{StaticStringVec, HTML_SPACE_CHARACTERS};
 use uuid::Uuid;
 
+pub struct OffThreadCompilationContext {
+    script_element: Trusted<HTMLScriptElement>,
+    script_kind: ExternalScriptKind,
+    final_url: ServoUrl,
+    url: ServoUrl,
+    task_source: DOMManipulationTaskSource,
+    canceller: TaskCanceller,
+    script_text: String,
+    utf16_chars: Vec<u16>,
+    fetch_options: ScriptFetchOptions,
+}
+
+/// A wrapper to mark OffThreadToken as Send,
+/// which should be safe according to
+/// mozjs/js/public/OffThreadScriptCompilation.h
+struct OffThreadCompilationToken(*mut OffThreadToken);
+
+#[allow(unsafe_code)]
+unsafe impl Send for OffThreadCompilationToken {}
+
+#[allow(unsafe_code)]
+unsafe extern "C" fn off_thread_compilation_callback(
+    token: *mut OffThreadToken,
+    callback_data: *mut c_void,
+) {
+    let mut context = Box::from_raw(callback_data as *mut OffThreadCompilationContext);
+    let token = OffThreadCompilationToken(token);
+
+    let url = context.url.clone();
+    let final_url = context.final_url.clone();
+    let script_element = context.script_element.clone();
+    let script_kind = context.script_kind.clone();
+    let script = replace(&mut context.script_text, String::new());
+    let fetch_options = context.fetch_options.clone();
+
+    // Continue with <https://html.spec.whatwg.org/multipage/#fetch-a-classic-script>
+    let _ = context.task_source.queue_with_canceller(
+        task!(off_thread_compile_continue: move || {
+            let elem = script_element.root();
+            let global = elem.global();
+            let cx = global.get_cx();
+            let _ar = enter_realm(&*global);
+
+            rooted!(in(*cx)
+                let compiled_script = FinishOffThreadScript(*cx, token.0)
+            );
+
+            let load = if compiled_script.get().is_null() {
+                Err(NetworkError::Internal(
+                    "Off-thread compilation failed.".into(),
+                ))
+            } else {
+                let script_text = DOMString::from(script);
+                let heap = Heap::default();
+                let source_code = RootedTraceableBox::new(heap);
+                source_code.set(compiled_script.get());
+                let code = SourceCode::Compiled(CompiledSourceCode {
+                    source_code: source_code,
+                    original_text: Rc::new(script_text),
+                });
+
+                Ok(ScriptOrigin {
+                    code,
+                    url: final_url,
+                    external: true,
+                    fetch_options: fetch_options,
+                    type_: ScriptType::Classic,
+                })
+            };
+
+            finish_fetching_a_classic_script(&*elem, script_kind, url, load);
+        }),
+        &context.canceller,
+    );
+}
+
 /// An unique id for script element.
 #[derive(Clone, Copy, Debug, Eq, Hash, JSTraceable, PartialEq)]
 pub struct ScriptId(Uuid);
@@ -151,9 +240,23 @@ pub enum ScriptType {
 }
 
 #[derive(JSTraceable, MallocSizeOf)]
+pub struct CompiledSourceCode {
+    #[ignore_malloc_size_of = "SM handles JS values"]
+    pub source_code: RootedTraceableBox<Heap<*mut JSScript>>,
+    #[ignore_malloc_size_of = "Rc is hard"]
+    pub original_text: Rc<DOMString>,
+}
+
+#[derive(JSTraceable)]
+pub enum SourceCode {
+    Text(Rc<DOMString>),
+    Compiled(CompiledSourceCode),
+}
+
+#[derive(JSTraceable, MallocSizeOf)]
 pub struct ScriptOrigin {
     #[ignore_malloc_size_of = "Rc is hard"]
-    text: Rc<DOMString>,
+    code: SourceCode,
     url: ServoUrl,
     external: bool,
     fetch_options: ScriptFetchOptions,
@@ -168,7 +271,7 @@ impl ScriptOrigin {
         type_: ScriptType,
     ) -> ScriptOrigin {
         ScriptOrigin {
-            text: text,
+            code: SourceCode::Text(text),
             url: url,
             external: false,
             fetch_options,
@@ -183,7 +286,7 @@ impl ScriptOrigin {
         type_: ScriptType,
     ) -> ScriptOrigin {
         ScriptOrigin {
-            text: text,
+            code: SourceCode::Text(text),
             url: url,
             external: true,
             fetch_options,
@@ -192,10 +295,37 @@ impl ScriptOrigin {
     }
 
     pub fn text(&self) -> Rc<DOMString> {
-        Rc::clone(&self.text)
+        match &self.code {
+            SourceCode::Text(text) => Rc::clone(&text),
+            SourceCode::Compiled(compiled_script) => Rc::clone(&compiled_script.original_text),
+        }
     }
 }
 
+/// Final steps of <https://html.spec.whatwg.org/multipage/#fetch-a-classic-script>
+fn finish_fetching_a_classic_script(
+    elem: &HTMLScriptElement,
+    script_kind: ExternalScriptKind,
+    url: ServoUrl,
+    load: ScriptResult,
+) {
+    // Step 11, Asynchronously complete this algorithm with script,
+    // which refers to step 26.6 "When the chosen algorithm asynchronously completes",
+    // of https://html.spec.whatwg.org/multipage/#prepare-a-script
+    let document = document_from_node(&*elem);
+
+    match script_kind {
+        ExternalScriptKind::Asap => document.asap_script_loaded(&elem, load),
+        ExternalScriptKind::AsapInOrder => document.asap_in_order_script_loaded(&elem, load),
+        ExternalScriptKind::Deferred => document.deferred_script_loaded(&elem, load),
+        ExternalScriptKind::ParsingBlocking => {
+            document.pending_parsing_blocking_script_loaded(&elem, load)
+        },
+    }
+
+    document.finish_load(LoadType::Script(url));
+}
+
 pub type ScriptResult = Result<ScriptOrigin, NetworkError>;
 
 /// The context required for asynchronously loading an external script source.
@@ -261,43 +391,79 @@ impl FetchResponseListener for ClassicContext {
 
     /// <https://html.spec.whatwg.org/multipage/#fetch-a-classic-script>
     /// step 4-9
+    #[allow(unsafe_code)]
     fn process_response_eof(&mut self, response: Result<ResourceFetchTiming, NetworkError>) {
-        // Step 5.
-        let load = response.and(self.status.clone()).map(|_| {
-            let metadata = self.metadata.take().unwrap();
-
-            // Step 6.
-            let encoding = metadata
-                .charset
-                .and_then(|encoding| Encoding::for_label(encoding.as_bytes()))
-                .unwrap_or(self.character_encoding);
+        let (source_text, final_url) = match (response.as_ref(), self.status.as_ref()) {
+            (Err(err), _) | (_, Err(err)) => {
+                // Step 6, response is an error.
+                finish_fetching_a_classic_script(
+                    &*self.elem.root(),
+                    self.kind.clone(),
+                    self.url.clone(),
+                    Err(err.clone()),
+                );
+                return;
+            },
+            (Ok(_), Ok(_)) => {
+                let metadata = self.metadata.take().unwrap();
+
+                // Step 7.
+                let encoding = metadata
+                    .charset
+                    .and_then(|encoding| Encoding::for_label(encoding.as_bytes()))
+                    .unwrap_or(self.character_encoding);
+
+                // Step 8.
+                let (source_text, _, _) = encoding.decode(&self.data);
+                (source_text, metadata.final_url)
+            },
+        };
 
-            // Step 7.
-            let (source_text, _, _) = encoding.decode(&self.data);
-            ScriptOrigin::external(
+        let elem = self.elem.root();
+        let global = elem.global();
+        let cx = global.get_cx();
+        let _ar = enter_realm(&*global);
+
+        let options =
+            unsafe { CompileOptionsWrapper::new(*cx, final_url.as_str().as_ptr() as *const i8, 1) };
+
+        let can_compile_off_thread = pref!(dom.script.asynch) &&
+            unsafe { CanCompileOffThread(*cx, options.ptr as *const _, source_text.len()) };
+
+        if can_compile_off_thread {
+            let source_string = source_text.to_string();
+            let source_text: Vec<u16> = source_text.encode_utf16().collect();
+
+            let context = Box::new(OffThreadCompilationContext {
+                script_element: self.elem.clone(),
+                script_kind: self.kind.clone(),
+                final_url,
+                url: self.url.clone(),
+                task_source: global.dom_manipulation_task_source(),
+                canceller: global.task_canceller(TaskSourceName::DOMManipulation),
+                script_text: source_string,
+                utf16_chars: source_text,
+                fetch_options: self.fetch_options.clone(),
+            });
+
+            unsafe {
+                assert!(CompileOffThread(
+                    *cx,
+                    options.ptr as *const _,
+                    &mut transform_u16_to_source_text(&context.utf16_chars) as *mut _,
+                    Some(off_thread_compilation_callback),
+                    Box::into_raw(context) as *mut c_void,
+                ));
+            }
+        } else {
+            let load = ScriptOrigin::external(
                 Rc::new(DOMString::from(source_text)),
-                metadata.final_url,
+                final_url.clone(),
                 self.fetch_options.clone(),
                 ScriptType::Classic,
-            )
-        });
-
-        // Step 9.
-        // https://html.spec.whatwg.org/multipage/#prepare-a-script
-        // Step 18.6 (When the chosen algorithm asynchronously completes).
-        let elem = self.elem.root();
-        let document = document_from_node(&*elem);
-
-        match self.kind {
-            ExternalScriptKind::Asap => document.asap_script_loaded(&elem, load),
-            ExternalScriptKind::AsapInOrder => document.asap_in_order_script_loaded(&elem, load),
-            ExternalScriptKind::Deferred => document.deferred_script_loaded(&elem, load),
-            ExternalScriptKind::ParsingBlocking => {
-                document.pending_parsing_blocking_script_loaded(&elem, load)
-            },
+            );
+            finish_fetching_a_classic_script(&*elem, self.kind.clone(), self.url.clone(), Ok(load));
         }
-
-        document.finish_load(LoadType::Script(self.url.clone()));
     }
 
     fn resource_timing_mut(&mut self) -> &mut ResourceFetchTiming {
@@ -702,7 +868,16 @@ impl HTMLScriptElement {
         // unminified content.
         let (input, output) = (tempfile::NamedTempFile::new(), tempfile::tempfile());
         if let (Ok(mut input), Ok(mut output)) = (input, output) {
-            input.write_all(script.text.as_bytes()).unwrap();
+            match &script.code {
+                SourceCode::Text(text) => {
+                    input.write_all(text.as_bytes()).unwrap();
+                },
+                SourceCode::Compiled(compiled_source_code) => {
+                    input
+                        .write_all(compiled_source_code.original_text.as_bytes())
+                        .unwrap();
+                },
+            }
             match Command::new("js-beautify")
                 .arg(input.path())
                 .stdout(output.try_clone().unwrap())
@@ -712,7 +887,7 @@ impl HTMLScriptElement {
                     let mut script_content = String::new();
                     output.seek(std::io::SeekFrom::Start(0)).unwrap();
                     output.read_to_string(&mut script_content).unwrap();
-                    script.text = Rc::new(DOMString::from(script_content));
+                    script.code = SourceCode::Text(Rc::new(DOMString::from(script_content)));
                 },
                 _ => {
                     warn!("Failed to execute js-beautify. Will store unmodified script");
@@ -763,7 +938,13 @@ impl HTMLScriptElement {
         debug!("script will be stored in {:?}", path);
 
         match File::create(&path) {
-            Ok(mut file) => file.write_all(script.text.as_bytes()).unwrap(),
+            Ok(mut file) => match &script.code {
+                SourceCode::Text(text) => file.write_all(text.as_bytes()).unwrap(),
+                SourceCode::Compiled(compiled_source_code) => {
+                    file.write_all(compiled_source_code.original_text.as_bytes())
+                        .unwrap();
+                },
+            },
             Err(why) => warn!("Could not store script {:?}", why),
         }
     }
@@ -790,7 +971,7 @@ impl HTMLScriptElement {
         match read_to_string(path.clone()) {
             Ok(local_script) => {
                 debug!("Found script stored at: {:?}", path);
-                script.text = Rc::new(DOMString::from(local_script));
+                script.code = SourceCode::Text(Rc::new(DOMString::from(local_script)));
             },
             Err(why) => warn!("Could not restore script from file {:?}", why),
         }
@@ -880,7 +1061,7 @@ impl HTMLScriptElement {
         rooted!(in(*window.get_cx()) let mut rval = UndefinedValue());
         let global = window.upcast::<GlobalScope>();
         global.evaluate_script_on_global_with_result(
-            &script.text,
+            &script.code,
             script.url.as_str(),
             rval.handle_mut(),
             line_number,
diff --git a/components/script/dom/userscripts.rs b/components/script/dom/userscripts.rs
index a004e0fe6b8..047b3345b0c 100644
--- a/components/script/dom/userscripts.rs
+++ b/components/script/dom/userscripts.rs
@@ -4,14 +4,17 @@
 
 use crate::dom::bindings::inheritance::Castable;
 use crate::dom::bindings::refcounted::Trusted;
+use crate::dom::bindings::str::DOMString;
 use crate::dom::globalscope::GlobalScope;
 use crate::dom::htmlheadelement::HTMLHeadElement;
+use crate::dom::htmlscriptelement::SourceCode;
 use crate::dom::node::document_from_node;
 use crate::script_module::ScriptFetchOptions;
 use js::jsval::UndefinedValue;
 use std::fs::{read_dir, File};
 use std::io::Read;
 use std::path::PathBuf;
+use std::rc::Rc;
 
 pub fn load_script(head: &HTMLHeadElement) {
     let doc = document_from_node(head);
@@ -38,7 +41,9 @@ pub fn load_script(head: &HTMLHeadElement) {
             let mut f = File::open(&file).unwrap();
             let mut contents = vec![];
             f.read_to_end(&mut contents).unwrap();
-            let script_text = String::from_utf8_lossy(&contents);
+            let script_text = SourceCode::Text(
+                Rc::new(DOMString::from_string(String::from_utf8_lossy(&contents).to_string()))
+            );
             let global = win.upcast::<GlobalScope>();
             global.evaluate_script_on_global_with_result(
                 &script_text,
diff --git a/resources/prefs.json b/resources/prefs.json
index d48175de8b4..ecb0e31faa0 100644
--- a/resources/prefs.json
+++ b/resources/prefs.json
@@ -18,6 +18,7 @@
   "dom.offscreen_canvas.enabled": false,
   "dom.permissions.enabled": false,
   "dom.permissions.testing.allowed_in_nonsecure_contexts": false,
+  "dom.script.asynch": true,
   "dom.serviceworker.enabled": false,
   "dom.serviceworker.timeout_seconds": 60,
   "dom.servo_helpers.enabled": false,
diff --git a/tests/wpt/metadata/custom-elements/customized-built-in-constructor-exceptions.html.ini b/tests/wpt/metadata/custom-elements/customized-built-in-constructor-exceptions.html.ini
deleted file mode 100644
index 10c7e55eab6..00000000000
--- a/tests/wpt/metadata/custom-elements/customized-built-in-constructor-exceptions.html.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[customized-built-in-constructor-exceptions.html]
-  expected: CRASH