Auto merge of #19126 - emilio:source-size-list, r=nox

style: Introduce SourceSizeList.

This is part of the work for https://bugzilla.mozilla.org/show_bug.cgi?id=1408308.

But this can just land now IMO, before I do the integration bits.

<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/19126)
<!-- Reviewable:end -->

components/style/gecko/media_queries.rs

@@ -10,7 +10,6 @@ use context::QuirksMode;
 use cssparser::{CssStringWriter, Parser, RGBA, Token, BasicParseErrorKind};
 use euclid::ScaleFactor;
 use euclid::Size2D;
-use font_metrics::get_metrics_provider_for_product;
 use gecko::values::{convert_nscolor_to_rgba, convert_rgba_to_nscolor};
 use gecko_bindings::bindings;
 use gecko_bindings::structs;
@@ -20,11 +19,9 @@ use gecko_bindings::structs::{nsMediaFeature_ValueType, nsMediaFeature_RangeType
 use gecko_bindings::structs::{nsPresContext, RawGeckoPresContextOwned};
 use media_queries::MediaType;
 use parser::ParserContext;
-use properties::{ComputedValues, StyleBuilder};
+use properties::ComputedValues;
 use properties::longhands::font_size;
-use rule_cache::RuleCacheConditions;
 use servo_arc::Arc;
-use std::cell::RefCell;
 use std::fmt::{self, Write};
 use std::sync::atomic::{AtomicBool, AtomicIsize, AtomicUsize, Ordering};
 use str::starts_with_ignore_ascii_case;
@@ -722,26 +719,8 @@ impl Expression {
                       self.feature.mRangeType == nsMediaFeature_RangeType::eMinMaxAllowed,
                       "Whoops, wrong range");
 
-        let default_values = device.default_computed_values();
-
-
-        let provider = get_metrics_provider_for_product();
-
         // http://dev.w3.org/csswg/mediaqueries3/#units
         // em units are relative to the initial font-size.
-        let mut conditions = RuleCacheConditions::default();
-        let context = computed::Context {
-            is_root_element: false,
-            builder: StyleBuilder::for_derived_style(device, default_values, None, None),
-            font_metrics_provider: &provider,
-            cached_system_font: None,
-            in_media_query: true,
-            quirks_mode,
-            for_smil_animation: false,
-            for_non_inherited_property: None,
-            rule_cache_conditions: RefCell::new(&mut conditions),
-        };
-
         let required_value = match self.value {
             Some(ref v) => v,
             None => {
@@ -750,7 +729,13 @@ impl Expression {
                 return match *actual_value {
                     BoolInteger(v) => v,
                     Integer(v) => v != 0,
-                    Length(ref l) => l.to_computed_value(&context).px() != 0.,
+                    Length(ref l) => {
+                        computed::Context::for_media_query_evaluation(
+                            device,
+                            quirks_mode,
+                            |context| l.to_computed_value(&context).px() != 0.,
+                        )
+                    },
                     _ => true,
                 }
             }
@@ -759,8 +744,10 @@ impl Expression {
         // FIXME(emilio): Handle the possible floating point errors?
         let cmp = match (required_value, actual_value) {
             (&Length(ref one), &Length(ref other)) => {
+                computed::Context::for_media_query_evaluation(device, quirks_mode, |context| {
                     one.to_computed_value(&context).to_i32_au()
                         .cmp(&other.to_computed_value(&context).to_i32_au())
+                })
             }
             (&Integer(one), &Integer(ref other)) => one.cmp(other),
             (&BoolInteger(one), &BoolInteger(ref other)) => one.cmp(other),

components/style/media_queries.rs

@@ -77,17 +77,10 @@ impl MediaQuery {
     /// Return a media query that never matches, used for when we fail to parse
     /// a given media query.
     fn never_matching() -> Self {
-        Self::new(Some(Qualifier::Not), MediaQueryType::All, vec![])
+        Self {
-    }
+            qualifier: Some(Qualifier::Not),
-
+            media_type: MediaQueryType::All,
-    /// Trivially constructs a new media query.
+            expressions: vec![],
-    pub fn new(qualifier: Option<Qualifier>,
-               media_type: MediaQueryType,
-               expressions: Vec<Expression>) -> MediaQuery {
-        MediaQuery {
-            qualifier: qualifier,
-            media_type: media_type,
-            expressions: expressions,
         }
     }
 }
@@ -209,9 +202,12 @@ impl MediaQuery {
 
         let media_type = match input.try(|i| i.expect_ident_cloned()) {
             Ok(ident) => {
-                let result: Result<_, ParseError> = MediaQueryType::parse(&*ident)
+                MediaQueryType::parse(&*ident)
-                    .map_err(|()| input.new_custom_error(SelectorParseErrorKind::UnexpectedIdent(ident.clone())));
+                    .map_err(|()| {
-                result?
+                        input.new_custom_error(
+                            SelectorParseErrorKind::UnexpectedIdent(ident.clone())
+                        )
+                    })?
             }
             Err(_) => {
                 // Media type is only optional if qualifier is not specified.
@@ -229,7 +225,7 @@ impl MediaQuery {
         // Parse any subsequent expressions
         loop {
             if input.try(|input| input.expect_ident_matching("and")).is_err() {
-                return Ok(MediaQuery::new(qualifier, media_type, expressions))
+                return Ok(MediaQuery { qualifier, media_type, expressions })
             }
             expressions.push(Expression::parse(context, input)?)
         }

components/style/servo/media_queries.rs

@@ -8,14 +8,11 @@ use app_units::Au;
 use context::QuirksMode;
 use cssparser::{Parser, RGBA};
 use euclid::{ScaleFactor, Size2D, TypedSize2D};
-use font_metrics::ServoMetricsProvider;
 use media_queries::MediaType;
 use parser::ParserContext;
-use properties::{ComputedValues, StyleBuilder};
+use properties::ComputedValues;
 use properties::longhands::font_size;
-use rule_cache::RuleCacheConditions;
 use selectors::parser::SelectorParseErrorKind;
-use std::cell::RefCell;
 use std::fmt;
 use std::sync::atomic::{AtomicBool, AtomicIsize, Ordering};
 use style_traits::{CSSPixel, DevicePixel, ToCss, ParseError};
@@ -252,29 +249,12 @@ pub enum Range<T> {
 
 impl Range<specified::Length> {
     fn to_computed_range(&self, device: &Device, quirks_mode: QuirksMode) -> Range<Au> {
-        let default_values = device.default_computed_values();
+        computed::Context::for_media_query_evaluation(device, quirks_mode, |context| {
-        let mut conditions = RuleCacheConditions::default();
-        // http://dev.w3.org/csswg/mediaqueries3/#units
-        // em units are relative to the initial font-size.
-        let context = computed::Context {
-            is_root_element: false,
-            builder: StyleBuilder::for_derived_style(device, default_values, None, None),
-            // Servo doesn't support font metrics
-            // A real provider will be needed here once we do; since
-            // ch units can exist in media queries.
-            font_metrics_provider: &ServoMetricsProvider,
-            in_media_query: true,
-            cached_system_font: None,
-            quirks_mode,
-            for_smil_animation: false,
-            for_non_inherited_property: None,
-            rule_cache_conditions: RefCell::new(&mut conditions),
-        };
-
             match *self {
                 Range::Min(ref width) => Range::Min(Au::from(width.to_computed_value(&context))),
                 Range::Max(ref width) => Range::Max(Au::from(width.to_computed_value(&context))),
                 Range::Eq(ref width) => Range::Eq(Au::from(width.to_computed_value(&context)))
             }
+        })
     }
 }

components/style/values/computed/mod.rs

@@ -7,7 +7,7 @@
 use {Atom, Namespace};
 use context::QuirksMode;
 use euclid::Size2D;
-use font_metrics::FontMetricsProvider;
+use font_metrics::{FontMetricsProvider, get_metrics_provider_for_product};
 use media_queries::Device;
 #[cfg(feature = "gecko")]
 use properties;
@@ -136,6 +136,36 @@ pub struct Context<'a> {
 }
 
 impl<'a> Context<'a> {
+    /// Creates a suitable context for media query evaluation, in which
+    /// font-relative units compute against the system_font, and executes `f`
+    /// with it.
+    pub fn for_media_query_evaluation<F, R>(
+        device: &Device,
+        quirks_mode: QuirksMode,
+        f: F,
+    ) -> R
+    where
+        F: FnOnce(&Context) -> R
+    {
+        let mut conditions = RuleCacheConditions::default();
+        let default_values = device.default_computed_values();
+        let provider = get_metrics_provider_for_product();
+
+        let context = Context {
+            is_root_element: false,
+            builder: StyleBuilder::for_derived_style(device, default_values, None, None),
+            font_metrics_provider: &provider,
+            cached_system_font: None,
+            in_media_query: true,
+            quirks_mode,
+            for_smil_animation: false,
+            for_non_inherited_property: None,
+            rule_cache_conditions: RefCell::new(&mut conditions),
+        };
+
+        f(&context)
+    }
+
     /// Whether the current element is the root element.
     pub fn is_root_element(&self) -> bool {
         self.is_root_element

components/style/values/specified/mod.rs

@@ -76,6 +76,7 @@ pub mod length;
 pub mod percentage;
 pub mod position;
 pub mod rect;
+pub mod source_size_list;
 pub mod svg;
 pub mod table;
 pub mod text;

components/style/values/specified/source_size_list.rs

@@ -0,0 +1,79 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! https://html.spec.whatwg.org/multipage/#source-size-list
+
+use app_units::Au;
+use cssparser::Parser;
+use media_queries::{Device, Expression as MediaExpression};
+use parser::{Parse, ParserContext};
+use selectors::context::QuirksMode;
+use style_traits::ParseError;
+use values::computed::{self, ToComputedValue};
+use values::specified::Length;
+
+/// A value for a `<source-size>`:
+///
+/// https://html.spec.whatwg.org/multipage/#source-size
+pub struct SourceSize {
+    condition: MediaExpression,
+    value: Length,
+}
+
+impl Parse for SourceSize {
+    fn parse<'i, 't>(
+        context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<Self, ParseError<'i>> {
+        let condition = MediaExpression::parse(context, input)?;
+        let value = Length::parse_non_negative(context, input)?;
+
+        Ok(Self { condition, value })
+    }
+}
+
+/// A value for a `<source-size-list>`:
+///
+/// https://html.spec.whatwg.org/multipage/#source-size-list
+pub struct SourceSizeList {
+    source_sizes: Vec<SourceSize>,
+    value: Length,
+}
+
+impl SourceSizeList {
+    /// Evaluate this <source-size-list> to get the final viewport length.
+    pub fn evaluate(&self, device: &Device, quirks_mode: QuirksMode) -> Au {
+        let matching_source_size = self.source_sizes.iter().find(|source_size| {
+            source_size.condition.matches(device, quirks_mode)
+        });
+
+        computed::Context::for_media_query_evaluation(device, quirks_mode, |context| {
+            match matching_source_size {
+                Some(source_size) => {
+                    source_size.value.to_computed_value(context)
+                }
+                None => {
+                    self.value.to_computed_value(context)
+                }
+            }
+        }).into()
+    }
+}
+
+impl Parse for SourceSizeList {
+    fn parse<'i, 't>(
+        context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<Self, ParseError<'i>> {
+        let source_sizes = input.try(|input| {
+            input.parse_comma_separated(|input| {
+                SourceSize::parse(context, input)
+            })
+        }).unwrap_or(vec![]);
+
+        let value = Length::parse_non_negative(context, input)?;
+
+        Ok(Self { source_sizes, value })
+    }
+}