Auto merge of #6185 - luniv:viewport-meta, r=mbrubeck

Implement <meta name=viewport> handling

Translate <meta name=viewport> as according to [CSS Device Adaption § 9](http://dev.w3.org/csswg/css-device-adapt/#viewport-meta)

Note: as the PR currently stands, handling `<meta name=viewport>` elements always occurs. This is probably not desired for some contexts (e.g. desktop), but I'm unsure of how to conditionally handle elements based on that.

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9 files changed, 508 insertions, 62 deletions

diff --git a/components/layout/layout_task.rs b/components/layout/layout_task.rs
index 3535b8137df..ee77270e62b 100644
--- a/components/layout/layout_task.rs
+++ b/components/layout/layout_task.rs
@@ -78,8 +78,9 @@ use style::media_queries::{Device, MediaQueryList, MediaType};
 use style::properties::longhands::{display, position};
 use style::properties::style_structs;
 use style::selector_matching::Stylist;
-use style::stylesheets::{CSSRuleIteratorExt, Origin, Stylesheet};
+use style::stylesheets::{CSSRule, CSSRuleIteratorExt, Origin, Stylesheet};
 use style::values::AuExtensionMethods;
+use style::viewport::ViewportRule;
 use url::Url;
 use util::geometry::{MAX_RECT, ZERO_POINT};
 use util::ipc::OptionalIpcSender;
@@ -618,6 +619,9 @@ impl LayoutTask {
                                             possibly_locked_rw_data)
             }
             Msg::SetQuirksMode => self.handle_set_quirks_mode(possibly_locked_rw_data),
+            Msg::AddMetaViewport(translated_rule) => {
+                self.handle_add_meta_viewport(translated_rule, possibly_locked_rw_data)
+            }
             Msg::GetRPC(response_chan) => {
                 response_chan.send(box LayoutRPCImpl(self.rw_data.clone()) as
                                    Box<LayoutRPC + Send>).unwrap();
@@ -823,6 +827,19 @@ impl LayoutTask {
         LayoutTask::return_rw_data(possibly_locked_rw_data, rw_data);
     }
 
+    fn handle_add_meta_viewport<'a>(&'a self,
+                                    translated_rule: ViewportRule,
+                                    possibly_locked_rw_data:
+                                      &mut Option<MutexGuard<'a, LayoutTaskData>>)
+    {
+        let mut rw_data = self.lock_rw_data(possibly_locked_rw_data);
+        rw_data.stylist.add_stylesheet(Stylesheet {
+            rules: vec![CSSRule::Viewport(translated_rule)],
+            origin: Origin::Author
+        });
+        LayoutTask::return_rw_data(possibly_locked_rw_data, rw_data);
+    }
+
     /// Sets quirks mode for the document, causing the quirks mode stylesheet to be loaded.
     fn handle_set_quirks_mode<'a>(&'a self,
                                   possibly_locked_rw_data:
@@ -1657,4 +1674,3 @@ fn get_root_flow_background_color(flow: &mut Flow) -> AzColor {
                   .resolve_color(kid_block_flow.fragment.style.get_background().background_color)
                   .to_gfx_color()
 }
-
diff --git a/components/script/dom/htmlmetaelement.rs b/components/script/dom/htmlmetaelement.rs
index 1bf78c66c8e..d7f4328bbfc 100644
--- a/components/script/dom/htmlmetaelement.rs
+++ b/components/script/dom/htmlmetaelement.rs
@@ -5,13 +5,18 @@
 use dom::bindings::codegen::Bindings::HTMLMetaElementBinding;
 use dom::bindings::codegen::Bindings::HTMLMetaElementBinding::HTMLMetaElementMethods;
 use dom::bindings::codegen::InheritTypes::HTMLMetaElementDerived;
-use dom::bindings::js::Root;
+use dom::bindings::codegen::InheritTypes::{ElementCast, HTMLElementCast, NodeCast};
+use dom::bindings::js::{Root, RootedReference};
 use dom::document::Document;
 use dom::element::ElementTypeId;
 use dom::eventtarget::{EventTarget, EventTargetTypeId};
 use dom::htmlelement::{HTMLElement, HTMLElementTypeId};
-use dom::node::{Node, NodeTypeId};
-use util::str::DOMString;
+use dom::node::{Node, NodeTypeId, window_from_node};
+use dom::virtualmethods::VirtualMethods;
+use layout_interface::{LayoutChan, Msg};
+use std::ascii::AsciiExt;
+use style::viewport::ViewportRule;
+use util::str::{DOMString, HTML_SPACE_CHARACTERS};
 
 #[dom_struct]
 pub struct HTMLMetaElement {
@@ -42,6 +47,35 @@ impl HTMLMetaElement {
         let element = HTMLMetaElement::new_inherited(localName, prefix, document);
         Node::reflect_node(box element, document, HTMLMetaElementBinding::Wrap)
     }
+
+    fn process_attributes(&self) {
+        let element = ElementCast::from_ref(self);
+        if let Some(name) = element.get_attribute(&ns!(""), &atom!("name")).r() {
+            let name = name.value().to_ascii_lowercase();
+            let name = name.trim_matches(HTML_SPACE_CHARACTERS);
+
+            match name {
+                "viewport" => self.translate_viewport(),
+                _ => {}
+            }
+        }
+    }
+
+    fn translate_viewport(&self) {
+        let element = ElementCast::from_ref(self);
+        if let Some(content) = element.get_attribute(&ns!(""), &atom!("content")).r() {
+            let content = content.value();
+            if !content.is_empty() {
+                if let Some(translated_rule) = ViewportRule::from_meta(&**content) {
+                    let node = NodeCast::from_ref(self);
+                    let win = window_from_node(node);
+                    let LayoutChan(ref layout_chan) = win.r().layout_chan();
+
+                    layout_chan.send(Msg::AddMetaViewport(translated_rule)).unwrap();
+                }
+            }
+        }
+    }
 }
 
 impl HTMLMetaElementMethods for HTMLMetaElement {
@@ -57,3 +91,20 @@ impl HTMLMetaElementMethods for HTMLMetaElement {
     // https://html.spec.whatwg.org/multipage/#dom-meta-content
     make_setter!(SetContent, "content");
 }
+
+impl VirtualMethods for HTMLMetaElement {
+    fn super_type<'b>(&'b self) -> Option<&'b VirtualMethods> {
+        let htmlelement: &HTMLElement = HTMLElementCast::from_ref(self);
+        Some(htmlelement as &VirtualMethods)
+    }
+
+    fn bind_to_tree(&self, tree_in_doc: bool) {
+        if let Some(ref s) = self.super_type() {
+            s.bind_to_tree(tree_in_doc);
+        }
+
+        if tree_in_doc {
+            self.process_attributes();
+        }
+    }
+}
diff --git a/components/script/dom/virtualmethods.rs b/components/script/dom/virtualmethods.rs
index 137843fb5ff..639b1ebd756 100644
--- a/components/script/dom/virtualmethods.rs
+++ b/components/script/dom/virtualmethods.rs
@@ -20,6 +20,7 @@ use dom::bindings::codegen::InheritTypes::HTMLIFrameElementCast;
 use dom::bindings::codegen::InheritTypes::HTMLImageElementCast;
 use dom::bindings::codegen::InheritTypes::HTMLInputElementCast;
 use dom::bindings::codegen::InheritTypes::HTMLLinkElementCast;
+use dom::bindings::codegen::InheritTypes::HTMLMetaElementCast;
 use dom::bindings::codegen::InheritTypes::HTMLObjectElementCast;
 use dom::bindings::codegen::InheritTypes::HTMLOptGroupElementCast;
 use dom::bindings::codegen::InheritTypes::HTMLOptionElementCast;
@@ -179,6 +180,10 @@ pub fn vtable_for<'a>(node: &'a Node) -> &'a (VirtualMethods + 'a) {
             let element = HTMLLinkElementCast::to_ref(node).unwrap();
             element as &'a (VirtualMethods + 'a)
         }
+        NodeTypeId::Element(ElementTypeId::HTMLElement(HTMLElementTypeId::HTMLMetaElement)) => {
+            let element = HTMLMetaElementCast::to_ref(node).unwrap();
+            element as &'a (VirtualMethods + 'a)
+        }
         NodeTypeId::Element(ElementTypeId::HTMLElement(HTMLElementTypeId::HTMLObjectElement)) => {
             let element = HTMLObjectElementCast::to_ref(node).unwrap();
             element as &'a (VirtualMethods + 'a)
diff --git a/components/script/layout_interface.rs b/components/script/layout_interface.rs
index 230ebe79692..9647ddd4376 100644
--- a/components/script/layout_interface.rs
+++ b/components/script/layout_interface.rs
@@ -28,6 +28,7 @@ use string_cache::Atom;
 use style::animation::PropertyAnimation;
 use style::media_queries::MediaQueryList;
 use style::stylesheets::Stylesheet;
+use style::viewport::ViewportRule;
 use url::Url;
 pub use dom::node::TrustedNodeAddress;
 
@@ -39,6 +40,9 @@ pub enum Msg {
     /// Adds the given stylesheet to the document.
     LoadStylesheet(Url, MediaQueryList, PendingAsyncLoad, Box<StylesheetLoadResponder + Send>),
 
+    /// Adds a @viewport rule (translated from a <META name="viewport"> element) to the document.
+    AddMetaViewport(ViewportRule),
+
     /// Puts a document into quirks mode, causing the quirks mode stylesheet to be loaded.
     SetQuirksMode,
 
diff --git a/components/style/viewport.rs b/components/style/viewport.rs
index f5bfd66e06d..3d3935ecb23 100644
--- a/components/style/viewport.rs
+++ b/components/style/viewport.rs
@@ -3,6 +3,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 use app_units::Au;
+use cssparser::ToCss;
 use cssparser::{AtRuleParser, DeclarationListParser, DeclarationParser, Parser, parse_important};
 use euclid::scale_factor::ScaleFactor;
 use euclid::size::{Size2D, TypedSize2D};
@@ -10,20 +11,23 @@ use parser::{ParserContext, log_css_error};
 use properties::longhands;
 use std::ascii::AsciiExt;
 use std::collections::hash_map::{Entry, HashMap};
+use std::fmt;
 use std::intrinsics;
+use std::iter::Enumerate;
+use std::str::Chars;
 use style_traits::viewport::{Orientation, UserZoom, ViewportConstraints, Zoom};
 use stylesheets::Origin;
 use util::geometry::ViewportPx;
 use values::computed::{Context, ToComputedValue};
-use values::specified::LengthOrPercentageOrAuto;
+use values::specified::{Length, LengthOrPercentageOrAuto, ViewportPercentageLength};
 
 #[derive(Copy, Clone, Debug, PartialEq)]
 pub enum ViewportDescriptor {
-    MinWidth(LengthOrPercentageOrAuto),
-    MaxWidth(LengthOrPercentageOrAuto),
+    MinWidth(ViewportLength),
+    MaxWidth(ViewportLength),
 
-    MinHeight(LengthOrPercentageOrAuto),
-    MaxHeight(LengthOrPercentageOrAuto),
+    MinHeight(ViewportLength),
+    MaxHeight(ViewportLength),
 
     Zoom(Zoom),
     MinZoom(Zoom),
@@ -33,6 +37,98 @@ pub enum ViewportDescriptor {
     Orientation(Orientation)
 }
 
+trait FromMeta: Sized {
+    fn from_meta<'a>(value: &'a str) -> Option<Self>;
+}
+
+// ViewportLength is a length | percentage | auto | extend-to-zoom
+// See:
+// * http://dev.w3.org/csswg/css-device-adapt/#min-max-width-desc
+// * http://dev.w3.org/csswg/css-device-adapt/#extend-to-zoom
+#[derive(Copy, Clone, Debug, HeapSizeOf, PartialEq)]
+pub enum ViewportLength {
+    Specified(LengthOrPercentageOrAuto),
+    ExtendToZoom
+}
+
+impl ToCss for ViewportLength {
+    fn to_css<W>(&self, dest: &mut W) -> fmt::Result
+        where W: fmt::Write
+    {
+        match *self {
+            ViewportLength::Specified(length) => length.to_css(dest),
+            ViewportLength::ExtendToZoom => write!(dest, "extend-to-zoom"),
+        }
+    }
+}
+
+impl FromMeta for ViewportLength {
+    fn from_meta<'a>(value: &'a str) -> Option<ViewportLength> {
+        macro_rules! specified {
+            ($value:expr) => {
+                ViewportLength::Specified(LengthOrPercentageOrAuto::Length($value))
+            }
+        }
+
+        Some(match value {
+            v if v.eq_ignore_ascii_case("device-width") =>
+                specified!(Length::ViewportPercentage(ViewportPercentageLength::Vw(100.))),
+            v if v.eq_ignore_ascii_case("device-height") =>
+                specified!(Length::ViewportPercentage(ViewportPercentageLength::Vh(100.))),
+            _ => {
+                match value.parse::<f32>() {
+                    Ok(n) if n >= 0. => specified!(Length::from_px(n.max(1.).min(10000.))),
+                    Ok(_) => return None,
+                    Err(_) => specified!(Length::from_px(1.))
+                }
+            }
+        })
+    }
+}
+
+impl ViewportLength {
+    fn parse(input: &mut Parser) -> Result<ViewportLength, ()> {
+        // we explicitly do not accept 'extend-to-zoom', since it is a UA internal value
+        // for <META> viewport translation
+        LengthOrPercentageOrAuto::parse_non_negative(input).map(ViewportLength::Specified)
+    }
+}
+
+impl FromMeta for Zoom {
+    fn from_meta<'a>(value: &'a str) -> Option<Zoom> {
+        Some(match value {
+            v if v.eq_ignore_ascii_case("yes") => Zoom::Number(1.),
+            v if v.eq_ignore_ascii_case("no") => Zoom::Number(0.1),
+            v if v.eq_ignore_ascii_case("device-width") => Zoom::Number(10.),
+            v if v.eq_ignore_ascii_case("device-height") => Zoom::Number(10.),
+            _ => {
+                match value.parse::<f32>() {
+                    Ok(n) if n >= 0. => Zoom::Number(n.max(0.1).min(10.)),
+                    Ok(_) => return None,
+                    Err(_) => Zoom::Number(0.1),
+                }
+            }
+        })
+    }
+}
+
+impl FromMeta for UserZoom {
+    fn from_meta<'a>(value: &'a str) -> Option<UserZoom> {
+        Some(match value {
+            v if v.eq_ignore_ascii_case("yes") => UserZoom::Zoom,
+            v if v.eq_ignore_ascii_case("no") => UserZoom::Fixed,
+            v if v.eq_ignore_ascii_case("device-width") => UserZoom::Zoom,
+            v if v.eq_ignore_ascii_case("device-height") => UserZoom::Zoom,
+            _ => {
+                match value.parse::<f32>() {
+                    Ok(n) if n >= 1. || n <= -1. => UserZoom::Zoom,
+                    _ => UserZoom::Fixed
+                }
+            }
+        })
+    }
+}
+
 struct ViewportRuleParser<'a, 'b: 'a> {
     context: &'a ParserContext<'b>
 }
@@ -57,10 +153,10 @@ impl ViewportDescriptorDeclaration {
     }
 }
 
-fn parse_shorthand(input: &mut Parser) -> Result<[LengthOrPercentageOrAuto; 2], ()> {
-    let min = try!(LengthOrPercentageOrAuto::parse_non_negative(input));
-    match input.try(|input| LengthOrPercentageOrAuto::parse_non_negative(input)) {
-        Err(()) => Ok([min.clone(), min]),
+fn parse_shorthand(input: &mut Parser) -> Result<[ViewportLength; 2], ()> {
+    let min = try!(ViewportLength::parse(input));
+    match input.try(|input| ViewportLength::parse(input)) {
+        Err(()) => Ok([min, min]),
         Ok(max) => Ok([min, max])
     }
 }
@@ -102,16 +198,16 @@ impl<'a, 'b> DeclarationParser for ViewportRuleParser<'a, 'b> {
 
         match name {
             n if n.eq_ignore_ascii_case("min-width") =>
-                ok!(MinWidth(LengthOrPercentageOrAuto::parse_non_negative)),
+                ok!(MinWidth(ViewportLength::parse)),
             n if n.eq_ignore_ascii_case("max-width") =>
-                ok!(MaxWidth(LengthOrPercentageOrAuto::parse_non_negative)),
+                ok!(MaxWidth(ViewportLength::parse)),
             n if n.eq_ignore_ascii_case("width") =>
                 ok!(shorthand -> [MinWidth, MaxWidth]),
 
             n if n.eq_ignore_ascii_case("min-height") =>
-                ok!(MinHeight(LengthOrPercentageOrAuto::parse_non_negative)),
+                ok!(MinHeight(ViewportLength::parse)),
             n if n.eq_ignore_ascii_case("max-height") =>
-                ok!(MaxHeight(LengthOrPercentageOrAuto::parse_non_negative)),
+                ok!(MaxHeight(ViewportLength::parse)),
             n if n.eq_ignore_ascii_case("height") =>
                 ok!(shorthand -> [MinHeight, MaxHeight]),
 
@@ -137,6 +233,19 @@ pub struct ViewportRule {
     pub declarations: Vec<ViewportDescriptorDeclaration>
 }
 
+/// Whitespace as defined by DEVICE-ADAPT § 9.2
+// TODO: should we just use whitespace as defined by HTML5?
+const WHITESPACE: &'static [char] = &['\t', '\n', '\r', ' '];
+
+/// Separators as defined by DEVICE-ADAPT § 9.2
+// need to use \x2c instead of ',' due to test-tidy
+const SEPARATOR: &'static [char] = &['\x2c', ';'];
+
+#[inline]
+fn is_whitespace_separator_or_equals(c: &char) -> bool {
+    WHITESPACE.contains(c) || SEPARATOR.contains(c) || *c == '='
+}
+
 impl ViewportRule {
     pub fn parse(input: &mut Parser, context: &ParserContext)
                      -> Result<ViewportRule, ()>
@@ -166,6 +275,145 @@ impl ViewportRule {
 
         Ok(ViewportRule { declarations: valid_declarations.iter().cascade() })
     }
+
+    pub fn from_meta<'a>(content: &'a str) -> Option<ViewportRule> {
+        let mut declarations = HashMap::new();
+        macro_rules! push_descriptor {
+            ($descriptor:ident($value:expr)) => {{
+                let descriptor = ViewportDescriptor::$descriptor($value);
+                declarations.insert(
+                    unsafe {
+                        intrinsics::discriminant_value(&descriptor)
+                    },
+                    ViewportDescriptorDeclaration::new(
+                        Origin::Author,
+                        descriptor,
+                        false))
+            }
+        }}
+
+        let mut has_width = false;
+        let mut has_height = false;
+        let mut has_zoom = false;
+
+        let mut iter = content.chars().enumerate();
+
+        macro_rules! start_of_name {
+            ($iter:ident) => {
+                $iter.by_ref()
+                    .skip_while(|&(_, c)| is_whitespace_separator_or_equals(&c))
+                    .next()
+            }
+        }
+
+        while let Some((start, _)) = start_of_name!(iter) {
+            let property = ViewportRule::parse_meta_property(content,
+                                                             &mut iter,
+                                                             start);
+
+            if let Some((name, value)) = property {
+                macro_rules! push {
+                    ($descriptor:ident($translate:path)) => {
+                        if let Some(value) = $translate(value) {
+                            push_descriptor!($descriptor(value));
+                        }
+                    }
+                }
+
+                match name {
+                    n if n.eq_ignore_ascii_case("width") => {
+                        if let Some(value) = ViewportLength::from_meta(value) {
+                            push_descriptor!(MinWidth(ViewportLength::ExtendToZoom));
+                            push_descriptor!(MaxWidth(value));
+                            has_width = true;
+                        }
+                    }
+                    n if n.eq_ignore_ascii_case("height") => {
+                        if let Some(value) = ViewportLength::from_meta(value) {
+                            push_descriptor!(MinHeight(ViewportLength::ExtendToZoom));
+                            push_descriptor!(MaxHeight(value));
+                            has_height = true;
+                        }
+                    }
+                    n if n.eq_ignore_ascii_case("initial-scale") => {
+                        if let Some(value) = Zoom::from_meta(value) {
+                            push_descriptor!(Zoom(value));
+                            has_zoom = true;
+                        }
+                    }
+                    n if n.eq_ignore_ascii_case("minimum-scale") =>
+                        push!(MinZoom(Zoom::from_meta)),
+                    n if n.eq_ignore_ascii_case("maximum-scale") =>
+                        push!(MaxZoom(Zoom::from_meta)),
+                    n if n.eq_ignore_ascii_case("user-scalable") =>
+                        push!(UserZoom(UserZoom::from_meta)),
+                    _ => {}
+                }
+            }
+        }
+
+        // DEVICE-ADAPT § 9.4 - The 'width' and 'height' properties
+        // http://dev.w3.org/csswg/css-device-adapt/#width-and-height-properties
+        if !has_width && has_zoom {
+            if has_height {
+                push_descriptor!(MinWidth(ViewportLength::Specified(LengthOrPercentageOrAuto::Auto)));
+                push_descriptor!(MaxWidth(ViewportLength::Specified(LengthOrPercentageOrAuto::Auto)));
+            } else {
+                push_descriptor!(MinWidth(ViewportLength::ExtendToZoom));
+                push_descriptor!(MaxWidth(ViewportLength::ExtendToZoom));
+            }
+        }
+
+        let declarations: Vec<_> = declarations.into_iter().map(|kv| kv.1).collect();
+        if !declarations.is_empty() {
+            Some(ViewportRule { declarations: declarations })
+        } else {
+            None
+        }
+    }
+
+    fn parse_meta_property<'a>(content: &'a str,
+                               iter: &mut Enumerate<Chars<'a>>,
+                               start: usize)
+                               -> Option<(&'a str, &'a str)>
+    {
+        fn end_of_token<'a>(iter: &mut Enumerate<Chars<'a>>) -> Option<(usize, char)> {
+            iter.by_ref()
+                .skip_while(|&(_, c)| !is_whitespace_separator_or_equals(&c))
+                .next()
+        }
+
+        fn skip_whitespace<'a>(iter: &mut Enumerate<Chars<'a>>) -> Option<(usize, char)> {
+            iter.by_ref()
+                .skip_while(|&(_, c)| WHITESPACE.contains(&c))
+                .next()
+        }
+
+        // <name> <whitespace>* '='
+        let end = match end_of_token(iter) {
+            Some((end, c)) if WHITESPACE.contains(&c) => {
+                match skip_whitespace(iter) {
+                    Some((_, c)) if c == '=' => end,
+                    _ => return None
+                }
+            }
+            Some((end, c)) if c == '=' => end,
+            _ => return None
+        };
+        let name = &content[start..end];
+
+        // <whitespace>* <value>
+        let start = match skip_whitespace(iter) {
+            Some((start, c)) if !SEPARATOR.contains(&c) => start,
+            _ => return None
+        };
+        let value = match end_of_token(iter) {
+            Some((end, _)) => &content[start..end],
+            _ => &content[start..]
+        };
+
+        Some((name, value))
+    }
 }
 
 pub trait ViewportRuleCascade: Iterator + Sized {
@@ -306,9 +554,9 @@ impl MaybeNew for ViewportConstraints {
             ($op:ident, $opta:expr, $optb:expr) => {
                 match ($opta, $optb) {
                     (None, None) => None,
-                    (a, None) => a.clone(),
-                    (None, b) => b.clone(),
-                    (a, b) => Some(a.clone().unwrap().$op(b.clone().unwrap())),
+                    (a, None) => a,
+                    (None, b) => b,
+                    (a, b) => Some(a.unwrap().$op(b.unwrap())),
                 }
             }
         }
@@ -325,7 +573,7 @@ impl MaybeNew for ViewportConstraints {
 
         // DEVICE-ADAPT § 6.2.1 Resolve min-zoom and max-zoom values
         if min_zoom.is_some() && max_zoom.is_some() {
-            max_zoom = Some(min_zoom.clone().unwrap().max(max_zoom.unwrap()))
+            max_zoom = Some(min_zoom.unwrap().max(max_zoom.unwrap()))
         }
 
         // DEVICE-ADAPT § 6.2.2 Constrain zoom value to the [min-zoom, max-zoom] range
@@ -363,18 +611,41 @@ impl MaybeNew for ViewportConstraints {
             outline_style_present: false,
         };
 
+        // DEVICE-ADAPT § 9.3 Resolving 'extend-to-zoom'
+        let extend_width;
+        let extend_height;
+        if let Some(extend_zoom) = max!(initial_zoom, max_zoom) {
+            let scale_factor = 1. / extend_zoom;
+            extend_width = Some(initial_viewport.width.scale_by(scale_factor));
+            extend_height = Some(initial_viewport.height.scale_by(scale_factor));
+        } else {
+            extend_width = None;
+            extend_height = None;
+        }
+
         macro_rules! to_pixel_length {
-            ($value:ident, $dimension:ident) => {
+            ($value:ident, $dimension:ident, $extend_to:ident => $auto_extend_to:expr) => {
                 if let Some($value) = $value {
                     match $value {
-                        LengthOrPercentageOrAuto::Length(value) =>
-                            Some(value.to_computed_value(&context)),
-                        LengthOrPercentageOrAuto::Percentage(value) =>
-                            Some(initial_viewport.$dimension.scale_by(value.0)),
-                        LengthOrPercentageOrAuto::Auto => None,
-                        LengthOrPercentageOrAuto::Calc(calc) => {
-                            let calc = calc.to_computed_value(&context);
-                            Some(initial_viewport.$dimension.scale_by(calc.percentage()) + calc.length())
+                        ViewportLength::Specified(length) => match length {
+                            LengthOrPercentageOrAuto::Length(value) =>
+                                Some(value.to_computed_value(&context)),
+                            LengthOrPercentageOrAuto::Percentage(value) =>
+                                Some(initial_viewport.$dimension.scale_by(value.0)),
+                            LengthOrPercentageOrAuto::Auto => None,
+                            LengthOrPercentageOrAuto::Calc(calc) => {
+                                let calc = calc.to_computed_value(&context);
+                                Some(initial_viewport.$dimension.scale_by(calc.percentage()) + calc.length())
+                            }
+                        },
+                        ViewportLength::ExtendToZoom => {
+                            // $extend_to will be 'None' if 'extend-to-zoom' is 'auto'
+                            match ($extend_to, $auto_extend_to) {
+                                (None, None) => None,
+                                (a, None) => a,
+                                (None, b) => b,
+                                (a, b) => cmp::max(a, b)
+                            }
                         }
                     }
                 } else {
@@ -383,10 +654,14 @@ impl MaybeNew for ViewportConstraints {
             }
         }
 
-        let min_width = to_pixel_length!(min_width, width);
-        let max_width = to_pixel_length!(max_width, width);
-        let min_height = to_pixel_length!(min_height, height);
-        let max_height = to_pixel_length!(max_height, height);
+        // DEVICE-ADAPT § 9.3 states that max-descriptors need to be resolved
+        // before min-descriptors.
+        // http://dev.w3.org/csswg/css-device-adapt/#resolve-extend-to-zoom
+        let max_width = to_pixel_length!(max_width, width, extend_width => None);
+        let max_height = to_pixel_length!(max_height, height, extend_height => None);
+
+        let min_width = to_pixel_length!(min_width, width, extend_width => max_width);
+        let min_height = to_pixel_length!(min_height, height, extend_height => max_height);
 
         // DEVICE-ADAPT § 6.2.4 Resolve initial width and height from min/max descriptors
         macro_rules! resolve {
@@ -421,7 +696,7 @@ impl MaybeNew for ViewportConstraints {
             Au(0) => initial_viewport.width,
             initial_height => {
                 let ratio = initial_viewport.width.to_f32_px() / initial_height.to_f32_px();
-                Au::from_f32_px(height.clone().unwrap().to_f32_px() * ratio)
+                Au::from_f32_px(height.unwrap().to_f32_px() * ratio)
             }
         });
 
diff --git a/tests/ref/basic.list b/tests/ref/basic.list
index 2a413231511..c823dd97d3d 100644
--- a/tests/ref/basic.list
+++ b/tests/ref/basic.list
@@ -397,6 +397,7 @@ flaky_cpu,prefs:"layout.writing-mode.enabled" == vertical-lr-blocks.html vertica
 == vertical_align_top_a.html vertical_align_top_ref.html
 == vertical_align_top_bottom_a.html vertical_align_top_bottom_ref.html
 == vertical_align_top_span_a.html vertical_align_top_span_ref.html
+== viewport_meta.html viewport_rule_ref.html
 resolution=800x600 == viewport_percentage_vmin_vmax.html viewport_percentage_vmin_vmax_a.html
 # resolution=600x800 == viewport_percentage_vmin_vmax.html viewport_percentage_vmin_vmax_b.html
 resolution=800x600 == viewport_percentage_vw_vh.html viewport_percentage_vw_vh_a.html
diff --git a/tests/ref/viewport_meta.html b/tests/ref/viewport_meta.html
new file mode 100644
index 00000000000..5c386bd7d76
--- /dev/null
+++ b/tests/ref/viewport_meta.html
@@ -0,0 +1,25 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <meta name="viewport" content="width=240">
+    <style>
+      #container {
+        background: blue;
+        height: 100vh;
+        width: 100vw;
+      }
+
+      #box {
+        background: green;
+        height: 50vh;
+        width: 50vw;
+      }
+    </style>
+  </head>
+  <body>
+    <div id="container">
+      <div id="box">
+      </div>
+    </div>
+  </body>
+</html>
diff --git a/tests/unit/style/lib.rs b/tests/unit/style/lib.rs
index 3c5d3a21004..e3b6684f4b9 100644
--- a/tests/unit/style/lib.rs
+++ b/tests/unit/style/lib.rs
@@ -3,6 +3,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #![feature(plugin)]
+#![cfg_attr(test, feature(core_intrinsics))]
 #![plugin(string_cache_plugin)]
 
 extern crate app_units;
diff --git a/tests/unit/style/viewport.rs b/tests/unit/style/viewport.rs
index bd1a2c0195a..31ae0a9e6c2 100644
--- a/tests/unit/style/viewport.rs
+++ b/tests/unit/style/viewport.rs
@@ -8,7 +8,9 @@ use euclid::size::Size2D;
 use style::media_queries::{Device, MediaType};
 use style::parser::ParserContext;
 use style::stylesheets::{Origin, Stylesheet, CSSRuleIteratorExt};
-use style::values::specified::{Length, LengthOrPercentageOrAuto};
+use style::values::specified::Length::{self, ViewportPercentage};
+use style::values::specified::LengthOrPercentageOrAuto::{self, Auto};
+use style::values::specified::ViewportPercentageLength::Vw;
 use style::viewport::*;
 use style_traits::viewport::*;
 use url::Url;
@@ -38,6 +40,26 @@ fn test_viewport_rule<F>(css: &str,
     assert!(rule_count > 0);
 }
 
+fn test_meta_viewport<F>(meta: &str, callback: F)
+    where F: Fn(&Vec<ViewportDescriptorDeclaration>, &str)
+{
+    if let Some(mut rule) = ViewportRule::from_meta(meta) {
+        use std::intrinsics::discriminant_value;
+
+        // from_meta uses a hash-map to collect the declarations, so we need to
+        // sort them in a stable order for the tests
+        rule.declarations.sort_by(|a, b| {
+            let a = unsafe { discriminant_value(&a.descriptor) };
+            let b = unsafe { discriminant_value(&b.descriptor) };
+            a.cmp(&b)
+        });
+
+        callback(&rule.declarations, meta);
+    } else {
+        panic!("no @viewport rule for {}", meta);
+    }
+}
+
 macro_rules! assert_decl_len {
     ($declarations:ident == 1) => {
         assert!($declarations.len() == 1,
@@ -51,6 +73,15 @@ macro_rules! assert_decl_len {
     }
 }
 
+macro_rules! viewport_length {
+    ($value:expr, px) => {
+        ViewportLength::Specified(LengthOrPercentageOrAuto::Length(Length::from_px($value)))
+    };
+    ($value:expr, vw) => {
+        ViewportLength::Specified(LengthOrPercentageOrAuto::Length(ViewportPercentage(Vw($value))))
+    }
+}
+
 #[test]
 fn empty_viewport_rule() {
     let device = Device::new(MediaType::Screen, Size2D::typed(800., 600.));
@@ -84,10 +115,10 @@ fn simple_viewport_rules() {
                        &device, |declarations, css| {
         println!("{}", css);
         assert_decl_len!(declarations == 9);
-        assert_decl_eq!(&declarations[0], Author, MinWidth: LengthOrPercentageOrAuto::Auto);
-        assert_decl_eq!(&declarations[1], Author, MaxWidth: LengthOrPercentageOrAuto::Auto);
-        assert_decl_eq!(&declarations[2], Author, MinHeight: LengthOrPercentageOrAuto::Auto);
-        assert_decl_eq!(&declarations[3], Author, MaxHeight: LengthOrPercentageOrAuto::Auto);
+        assert_decl_eq!(&declarations[0], Author, MinWidth: ViewportLength::Specified(Auto));
+        assert_decl_eq!(&declarations[1], Author, MaxWidth: ViewportLength::Specified(Auto));
+        assert_decl_eq!(&declarations[2], Author, MinHeight: ViewportLength::Specified(Auto));
+        assert_decl_eq!(&declarations[3], Author, MaxHeight: ViewportLength::Specified(Auto));
         assert_decl_eq!(&declarations[4], Author, Zoom: Zoom::Auto);
         assert_decl_eq!(&declarations[5], Author, MinZoom: Zoom::Number(0.));
         assert_decl_eq!(&declarations[6], Author, MaxZoom: Zoom::Percentage(2.));
@@ -100,10 +131,49 @@ fn simple_viewport_rules() {
                        &device, |declarations, css| {
         println!("{}", css);
         assert_decl_len!(declarations == 4);
-        assert_decl_eq!(&declarations[0], Author, MinWidth: LengthOrPercentageOrAuto::Length(Length::from_px(200.)));
-        assert_decl_eq!(&declarations[1], Author, MaxWidth: LengthOrPercentageOrAuto::Auto);
-        assert_decl_eq!(&declarations[2], Author, MinHeight: LengthOrPercentageOrAuto::Length(Length::from_px(200.)));
-        assert_decl_eq!(&declarations[3], Author, MaxHeight: LengthOrPercentageOrAuto::Auto);
+        assert_decl_eq!(&declarations[0], Author, MinWidth: viewport_length!(200., px));
+        assert_decl_eq!(&declarations[1], Author, MaxWidth: ViewportLength::Specified(Auto));
+        assert_decl_eq!(&declarations[2], Author, MinHeight: viewport_length!(200., px));
+        assert_decl_eq!(&declarations[3], Author, MaxHeight: ViewportLength::Specified(Auto));
+    });
+}
+
+#[test]
+fn simple_meta_viewport_contents() {
+    test_meta_viewport("width=500, height=600", |declarations, meta| {
+        println!("{}", meta);
+        assert_decl_len!(declarations == 4);
+        assert_decl_eq!(&declarations[0], Author, MinWidth: ViewportLength::ExtendToZoom);
+        assert_decl_eq!(&declarations[1], Author, MaxWidth: viewport_length!(500., px));
+        assert_decl_eq!(&declarations[2], Author, MinHeight: ViewportLength::ExtendToZoom);
+        assert_decl_eq!(&declarations[3], Author, MaxHeight: viewport_length!(600., px));
+    });
+
+    test_meta_viewport("initial-scale=1.0", |declarations, meta| {
+        println!("{}", meta);
+        assert_decl_len!(declarations == 3);
+        assert_decl_eq!(&declarations[0], Author, MinWidth: ViewportLength::ExtendToZoom);
+        assert_decl_eq!(&declarations[1], Author, MaxWidth: ViewportLength::ExtendToZoom);
+        assert_decl_eq!(&declarations[2], Author, Zoom: Zoom::Number(1.));
+    });
+
+    test_meta_viewport("initial-scale=2.0, height=device-width", |declarations, meta| {
+        println!("{}", meta);
+        assert_decl_len!(declarations == 5);
+        assert_decl_eq!(&declarations[0], Author, MinWidth: ViewportLength::Specified(Auto));
+        assert_decl_eq!(&declarations[1], Author, MaxWidth: ViewportLength::Specified(Auto));
+        assert_decl_eq!(&declarations[2], Author, MinHeight: ViewportLength::ExtendToZoom);
+        assert_decl_eq!(&declarations[3], Author, MaxHeight: viewport_length!(100., vw));
+        assert_decl_eq!(&declarations[4], Author, Zoom: Zoom::Number(2.));
+    });
+
+    test_meta_viewport("width=480, initial-scale=2.0, user-scalable=1", |declarations, meta| {
+        println!("{}", meta);
+        assert_decl_len!(declarations == 4);
+        assert_decl_eq!(&declarations[0], Author, MinWidth: ViewportLength::ExtendToZoom);
+        assert_decl_eq!(&declarations[1], Author, MaxWidth: viewport_length!(480., px));
+        assert_decl_eq!(&declarations[2], Author, Zoom: Zoom::Number(2.));
+        assert_decl_eq!(&declarations[3], Author, UserZoom: UserZoom::Zoom);
     });
 }
 
@@ -116,7 +186,7 @@ fn cascading_within_viewport_rule() {
                        &device, |declarations, css| {
         println!("{}", css);
         assert_decl_len!(declarations == 1);
-        assert_decl_eq!(&declarations[0], Author, MinWidth: LengthOrPercentageOrAuto::Auto);
+        assert_decl_eq!(&declarations[0], Author, MinWidth: ViewportLength::Specified(Auto));
     });
 
     // !important order of appearance
@@ -124,7 +194,7 @@ fn cascading_within_viewport_rule() {
                        &device, |declarations, css| {
         println!("{}", css);
         assert_decl_len!(declarations == 1);
-        assert_decl_eq!(&declarations[0], Author, MinWidth: LengthOrPercentageOrAuto::Auto, !important);
+        assert_decl_eq!(&declarations[0], Author, MinWidth: ViewportLength::Specified(Auto), !important);
     });
 
     // !important vs normal
@@ -132,7 +202,7 @@ fn cascading_within_viewport_rule() {
                        &device, |declarations, css| {
         println!("{}", css);
         assert_decl_len!(declarations == 1);
-        assert_decl_eq!(&declarations[0], Author, MinWidth: LengthOrPercentageOrAuto::Auto, !important);
+        assert_decl_eq!(&declarations[0], Author, MinWidth: ViewportLength::Specified(Auto), !important);
     });
 
     // normal longhands vs normal shorthand
@@ -140,8 +210,8 @@ fn cascading_within_viewport_rule() {
                        &device, |declarations, css| {
         println!("{}", css);
         assert_decl_len!(declarations == 2);
-        assert_decl_eq!(&declarations[0], Author, MinWidth: LengthOrPercentageOrAuto::Auto);
-        assert_decl_eq!(&declarations[1], Author, MaxWidth: LengthOrPercentageOrAuto::Auto);
+        assert_decl_eq!(&declarations[0], Author, MinWidth: ViewportLength::Specified(Auto));
+        assert_decl_eq!(&declarations[1], Author, MaxWidth: ViewportLength::Specified(Auto));
     });
 
     // normal shorthand vs normal longhands
@@ -149,8 +219,8 @@ fn cascading_within_viewport_rule() {
                        &device, |declarations, css| {
         println!("{}", css);
         assert_decl_len!(declarations == 2);
-        assert_decl_eq!(&declarations[0], Author, MinWidth: LengthOrPercentageOrAuto::Auto);
-        assert_decl_eq!(&declarations[1], Author, MaxWidth: LengthOrPercentageOrAuto::Auto);
+        assert_decl_eq!(&declarations[0], Author, MinWidth: ViewportLength::Specified(Auto));
+        assert_decl_eq!(&declarations[1], Author, MaxWidth: ViewportLength::Specified(Auto));
     });
 
     // one !important longhand vs normal shorthand
@@ -158,8 +228,8 @@ fn cascading_within_viewport_rule() {
                        &device, |declarations, css| {
         println!("{}", css);
         assert_decl_len!(declarations == 2);
-        assert_decl_eq!(&declarations[0], Author, MinWidth: LengthOrPercentageOrAuto::Auto, !important);
-        assert_decl_eq!(&declarations[1], Author, MaxWidth: LengthOrPercentageOrAuto::Length(Length::from_px(200.)));
+        assert_decl_eq!(&declarations[0], Author, MinWidth: ViewportLength::Specified(Auto), !important);
+        assert_decl_eq!(&declarations[1], Author, MaxWidth: viewport_length!(200., px));
     });
 
     // both !important longhands vs normal shorthand
@@ -167,8 +237,8 @@ fn cascading_within_viewport_rule() {
                        &device, |declarations, css| {
         println!("{}", css);
         assert_decl_len!(declarations == 2);
-        assert_decl_eq!(&declarations[0], Author, MinWidth: LengthOrPercentageOrAuto::Auto, !important);
-        assert_decl_eq!(&declarations[1], Author, MaxWidth: LengthOrPercentageOrAuto::Auto, !important);
+        assert_decl_eq!(&declarations[0], Author, MinWidth: ViewportLength::Specified(Auto), !important);
+        assert_decl_eq!(&declarations[1], Author, MaxWidth: ViewportLength::Specified(Auto), !important);
     });
 }
 
@@ -189,8 +259,8 @@ fn multiple_stylesheets_cascading() {
         .declarations;
     assert_decl_len!(declarations == 3);
     assert_decl_eq!(&declarations[0], UserAgent, Zoom: Zoom::Number(1.));
-    assert_decl_eq!(&declarations[1], User, MinHeight: LengthOrPercentageOrAuto::Length(Length::from_px(200.)));
-    assert_decl_eq!(&declarations[2], Author, MinWidth: LengthOrPercentageOrAuto::Length(Length::from_px(300.)));
+    assert_decl_eq!(&declarations[1], User, MinHeight: viewport_length!(200., px));
+    assert_decl_eq!(&declarations[2], Author, MinWidth: viewport_length!(300., px));
 
     let stylesheets = vec![
         stylesheet!("@viewport { min-width: 100px !important; }", UserAgent),
@@ -203,10 +273,8 @@ fn multiple_stylesheets_cascading() {
         .cascade()
         .declarations;
     assert_decl_len!(declarations == 3);
-    assert_decl_eq!(
-        &declarations[0], UserAgent, MinWidth: LengthOrPercentageOrAuto::Length(Length::from_px(100.)), !important);
-    assert_decl_eq!(
-        &declarations[1], User, MinHeight: LengthOrPercentageOrAuto::Length(Length::from_px(200.)), !important);
+    assert_decl_eq!(&declarations[0], UserAgent, MinWidth: viewport_length!(100., px), !important);
+    assert_decl_eq!(&declarations[1], User, MinHeight: viewport_length!(200., px), !important);
     assert_decl_eq!(&declarations[2], Author, Zoom: Zoom::Number(3.), !important);
 }