Bug 1331213: Bootstrap a Gecko-side Device, and track it's dirtiness manually in the per-doc data. r=heycam

The setup is quite different to Servo-land, so add a comment about the different
setup.

Also, check viewport rules when flushing stylesheets. I believe that the
previous behavior is plain wrong, though I haven't taken the time to come up
with a test case.

In any case, it doesn't hurt any of both back-ends.

MozReview-Commit-ID: 46gtTkesOsr
Signed-off-by: Emilio Cobos Álvarez <emilio@crisal.io>

components/style/gecko/media_queries.rs

@@ -0,0 +1,359 @@
+/* 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/. */
+
+//! Gecko's media-query device and expression representation.
+
+use app_units::Au;
+use cssparser::{Parser, Token};
+use euclid::Size2D;
+use gecko_bindings::bindings;
+use gecko_bindings::structs::{nsMediaExpression_Range, nsMediaFeature};
+use gecko_bindings::structs::{nsMediaFeature_ValueType, nsMediaFeature_RangeType, nsMediaFeature_RequirementFlags};
+use gecko_bindings::structs::RawGeckoPresContextOwned;
+use media_queries::MediaType;
+use properties::ComputedValues;
+use std::ascii::AsciiExt;
+use std::fmt;
+use std::sync::Arc;
+use string_cache::Atom;
+use style_traits::ToCss;
+use style_traits::viewport::ViewportConstraints;
+use values::{CSSFloat, specified};
+
+/// The `Device` in Gecko wraps a pres context, has a default values computed,
+/// and contains all the viewport rule state.
+pub struct Device {
+    /// NB: The pres context lifetime is tied to the styleset, who owns the
+    /// stylist, and thus the `Device`, so having a raw pres context pointer
+    /// here is fine.
+    pres_context: RawGeckoPresContextOwned,
+    default_values: Arc<ComputedValues>,
+    viewport_override: Option<ViewportConstraints>,
+}
+
+impl Device {
+    /// Trivially constructs a new `Device`.
+    pub fn new(pres_context: RawGeckoPresContextOwned) -> Self {
+        assert!(!pres_context.is_null());
+        Device {
+            pres_context: pres_context,
+            default_values: ComputedValues::default_values(unsafe { &*pres_context }),
+            viewport_override: None,
+        }
+    }
+
+    /// Tells the device that a new viewport rule has been found, and stores the
+    /// relevant viewport constraints.
+    pub fn account_for_viewport_rule(&mut self,
+                                     constraints: &ViewportConstraints) {
+        self.viewport_override = Some(constraints.clone());
+    }
+
+    /// Returns the default computed values as a reference, in order to match
+    /// Servo.
+    pub fn default_values(&self) -> &ComputedValues {
+        &*self.default_values
+    }
+
+    /// Returns the default computed values as an `Arc`, in order to avoid
+    /// clones.
+    pub fn default_values_arc(&self) -> &Arc<ComputedValues> {
+        &self.default_values
+    }
+
+    /// Recreates all the temporary state that the `Device` stores.
+    ///
+    /// This includes the viewport override from `@viewport` rules, and also the
+    /// default computed values.
+    pub fn reset(&mut self) {
+        // NB: A following stylesheet flush will populate this if appropriate.
+        self.viewport_override = None;
+        self.default_values = ComputedValues::default_values(unsafe { &*self.pres_context });
+    }
+
+    /// Returns the current media type of the device.
+    pub fn media_type(&self) -> MediaType {
+        // TODO
+        MediaType::Screen
+    }
+
+    /// Returns the current viewport size in app units.
+    pub fn au_viewport_size(&self) -> Size2D<Au> {
+        self.viewport_override.as_ref().map(|v| {
+            Size2D::new(Au::from_f32_px(v.size.width),
+                        Au::from_f32_px(v.size.height))
+        }).unwrap_or_else(|| {
+            // TODO(emilio): Grab from pres context.
+            Size2D::new(Au::from_f32_px(1024.0),
+                        Au::from_f32_px(768.0))
+        })
+    }
+}
+
+unsafe impl Sync for Device {}
+unsafe impl Send for Device {}
+
+/// A expression for gecko contains a reference to the media feature, the value
+/// the media query contained, and the range to evaluate.
+#[derive(Debug, Clone)]
+pub struct Expression {
+    feature: &'static nsMediaFeature,
+    value: MediaExpressionValue,
+    range: nsMediaExpression_Range
+}
+
+impl ToCss for Expression {
+    fn to_css<W>(&self, dest: &mut W) -> fmt::Result
+        where W: fmt::Write,
+    {
+        dest.write_str("(")?;
+        match self.range {
+            nsMediaExpression_Range::eMin => dest.write_str("min-")?,
+            nsMediaExpression_Range::eMax => dest.write_str("max-")?,
+            nsMediaExpression_Range::eEqual => {},
+        }
+        // NB: CSSStringWriter not needed, features are under control.
+        write!(dest, "{}", Atom::from(unsafe { *self.feature.mName }))?;
+        dest.write_str(": ")?;
+
+        self.value.to_css(dest)?;
+        dest.write_str(")")
+    }
+}
+
+/// A resolution.
+#[derive(Debug, Clone)]
+pub enum Resolution {
+    /// Dots per inch.
+    Dpi(CSSFloat),
+    /// Dots per pixel.
+    Dppx(CSSFloat),
+    /// Dots per centimeter.
+    Dpcm(CSSFloat),
+}
+
+impl Resolution {
+    fn parse(input: &mut Parser) -> Result<Self, ()> {
+        let (value, unit) = match try!(input.next()) {
+            Token::Dimension(value, unit) => {
+                (value.value, unit)
+            },
+            _ => return Err(()),
+        };
+
+        Ok(match_ignore_ascii_case! { unit,
+            "dpi" => Resolution::Dpi(value),
+            "dppx" => Resolution::Dppx(value),
+            "dpcm" => Resolution::Dpcm(value),
+            _ => return Err(())
+        })
+    }
+}
+
+impl ToCss for Resolution {
+    fn to_css<W>(&self, dest: &mut W) -> fmt::Result
+        where W: fmt::Write,
+    {
+        match *self {
+            Resolution::Dpi(v) => write!(dest, "{}dpi", v),
+            Resolution::Dppx(v) => write!(dest, "{}dppx", v),
+            Resolution::Dpcm(v) => write!(dest, "{}dpcm", v),
+        }
+    }
+}
+
+/// A value found or expected in a media expression.
+#[derive(Debug, Clone)]
+pub enum MediaExpressionValue {
+    /// A length.
+    Length(specified::Length),
+    /// A (non-negative) integer.
+    Integer(u32),
+    /// A floating point value.
+    Float(CSSFloat),
+    /// A boolean value, specified as an integer (i.e., either 0 or 1).
+    BoolInteger(bool),
+    /// Two integers separated by '/', with optional whitespace on either side
+    /// of the '/'.
+    IntRatio(u32, u32),
+    /// A resolution.
+    Resolution(Resolution),
+    /// An enumerated index into the variant keyword table.
+    Enumerated(u32),
+    /// An identifier.
+    Ident(Atom),
+}
+
+impl ToCss for MediaExpressionValue {
+    fn to_css<W>(&self, dest: &mut W) -> fmt::Result
+        where W: fmt::Write,
+    {
+        match *self {
+            MediaExpressionValue::Length(ref l) => l.to_css(dest),
+            MediaExpressionValue::Integer(v) => write!(dest, "{}", v),
+            MediaExpressionValue::Float(v) => write!(dest, "{}", v),
+            MediaExpressionValue::BoolInteger(v) => {
+                dest.write_str(if v { "1" } else { "0" })
+            },
+            MediaExpressionValue::IntRatio(a, b) => {
+                write!(dest, "{}/{}", a, b)
+            },
+            MediaExpressionValue::Resolution(ref r) => r.to_css(dest),
+            MediaExpressionValue::Enumerated(..) |
+            MediaExpressionValue::Ident(..) => {
+                // TODO(emilio)
+                unimplemented!()
+            }
+        }
+    }
+}
+
+fn starts_with_ignore_ascii_case(string: &str, prefix: &str) -> bool {
+    string.len() > prefix.len() &&
+      string[0..prefix.len()].eq_ignore_ascii_case(prefix)
+}
+
+#[allow(warnings)]
+fn find_feature<F>(mut f: F) -> Option<&'static nsMediaFeature>
+    where F: FnMut(&'static nsMediaFeature) -> bool,
+{
+    // FIXME(emilio): With build-time bindgen, we would be able to use
+    // structs::nsMediaFeatures_features. That would unfortunately break MSVC
+    // builds, or require one bindings file per platform.
+    //
+    // I'm not into any of those, so meanwhile let's use a FFI function.
+    unsafe {
+        let mut features = bindings::Gecko_GetMediaFeatures();
+        while !(*features).mName.is_null() {
+            if f(&*features) {
+                return Some(&*features);
+            }
+            features = features.offset(1);
+        }
+    }
+
+    None
+}
+
+impl Expression {
+    /// Trivially construct a new expression.
+    fn new(feature: &'static nsMediaFeature,
+           value: MediaExpressionValue,
+           range: nsMediaExpression_Range) -> Self {
+        Expression {
+            feature: feature,
+            value: value,
+            range: range,
+        }
+    }
+
+    /// Parse a media expression of the form:
+    ///
+    /// ```
+    /// (media-feature: media-value)
+    /// ```
+    #[allow(warnings)]
+    pub fn parse(input: &mut Parser) -> Result<Self, ()> {
+        try!(input.expect_parenthesis_block());
+        input.parse_nested_block(|input| {
+            let ident = try!(input.expect_ident());
+            try!(input.expect_colon());
+
+            let mut flags = 0;
+            let mut feature_name = &*ident;
+
+            // TODO(emilio): this is under a pref in Gecko.
+            if starts_with_ignore_ascii_case(feature_name, "-webkit-") {
+                feature_name = &feature_name[8..];
+                flags |= nsMediaFeature_RequirementFlags::eHasWebkitPrefix as u8;
+            }
+
+            let range = if starts_with_ignore_ascii_case(feature_name, "min-") {
+                feature_name = &feature_name[4..];
+                nsMediaExpression_Range::eMin
+            } else if starts_with_ignore_ascii_case(feature_name, "max-") {
+                feature_name = &feature_name[4..];
+                nsMediaExpression_Range::eMax
+            } else {
+                nsMediaExpression_Range::eEqual
+            };
+
+            let atom = Atom::from(feature_name);
+            let feature =
+                match find_feature(|f| atom.as_ptr() == unsafe { *f.mName }) {
+                    Some(f) => f,
+                    None => return Err(()),
+                };
+
+            if (feature.mReqFlags & !flags) != 0 {
+                return Err(());
+            }
+
+            if range != nsMediaExpression_Range::eEqual &&
+                feature.mRangeType != nsMediaFeature_RangeType::eMinMaxAllowed {
+                return Err(());
+            }
+
+            let value = match feature.mValueType {
+                nsMediaFeature_ValueType::eLength => {
+                    MediaExpressionValue::Length(
+                        specified::Length::parse_non_negative(input)?)
+                },
+                nsMediaFeature_ValueType::eInteger => {
+                    let i = input.expect_integer()?;
+                    if i < 0 {
+                        return Err(())
+                    }
+                    MediaExpressionValue::Integer(i as u32)
+                }
+                nsMediaFeature_ValueType::eBoolInteger => {
+                    let i = input.expect_integer()?;
+                    if i < 0 || i > 1 {
+                        return Err(())
+                    }
+                    MediaExpressionValue::BoolInteger(i == 1)
+                }
+                nsMediaFeature_ValueType::eFloat => {
+                    MediaExpressionValue::Float(input.expect_number()?)
+                }
+                nsMediaFeature_ValueType::eIntRatio => {
+                    let a = input.expect_integer()?;
+                    if a <= 0 {
+                        return Err(())
+                    }
+
+                    input.expect_delim('/')?;
+
+                    let b = input.expect_integer()?;
+                    if b <= 0 {
+                        return Err(())
+                    }
+                    MediaExpressionValue::IntRatio(a as u32, b as u32)
+                }
+                nsMediaFeature_ValueType::eResolution => {
+                    MediaExpressionValue::Resolution(Resolution::parse(input)?)
+                }
+                nsMediaFeature_ValueType::eEnumerated => {
+                    let index = unsafe {
+                        let _table = feature.mData.mKeywordTable.as_ref();
+                        0
+                    };
+                    MediaExpressionValue::Enumerated(index)
+                }
+                nsMediaFeature_ValueType::eIdent => {
+                    MediaExpressionValue::Ident(input.expect_ident()?.into())
+                }
+            };
+
+            Ok(Expression::new(feature, value, range))
+        })
+    }
+
+    /// Returns whether this media query evaluates to true for the given
+    /// device.
+    pub fn matches(&self, _device: &Device) -> bool {
+        // TODO
+        false
+    }
+}