servo: Merge #16959 - Font serialization for canvas (from hiikezoe:font-serialization-for-canvas); r=Manishearth,emilio

<!-- Please describe your changes on the following line: -->
This is a PR for https://bugzilla.mozilla.org/show_bug.cgi?id=1362914
---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes do not require tests because it's for stylo

Source-Repo: https://github.com/servo/servo
Source-Revision: 8cd4330b2afdaf6f5a1724539a25a27850d41e29

--HG--
extra : subtree_source : https%3A//hg.mozilla.org/projects/converted-servo-linear
extra : subtree_revision : 6da2098f9c326659f9bae725f89714ce908edf12

servo/components/style/gecko/generated/bindings.rs

@@ -2471,6 +2471,11 @@ extern "C" {
                                                               CSSPseudoElementType)
      -> ServoComputedValuesStrong;
 }
+extern "C" {
+    pub fn Servo_SerializeFontValueForCanvas(declarations:
+                                                 RawServoDeclarationBlockBorrowed,
+                                             buffer: *mut nsAString);
+}
 extern "C" {
     pub fn Servo_GetStyleFont(computed_values:
                                   ServoComputedValuesBorrowedOrNull)

servo/components/style/gecko/generated/structs_debug.rs

@@ -34192,7 +34192,7 @@ pub mod root {
                    root::nsCharTraits ) ));
     }
     #[test]
-    fn __bindgen_test_layout__bindgen_ty_id_210589_instantiation_99() {
+    fn __bindgen_test_layout__bindgen_ty_id_210592_instantiation_99() {
         assert_eq!(::std::mem::size_of::<u8>() , 1usize , concat ! (
                    "Size of template specialization: " , stringify ! ( u8 )
                    ));
@@ -34201,7 +34201,7 @@ pub mod root {
                    ) ));
     }
     #[test]
-    fn __bindgen_test_layout__bindgen_ty_id_210625_instantiation_100() {
+    fn __bindgen_test_layout__bindgen_ty_id_210628_instantiation_100() {
         assert_eq!(::std::mem::size_of::<u8>() , 1usize , concat ! (
                    "Size of template specialization: " , stringify ! ( u8 )
                    ));

servo/components/style/gecko/generated/structs_release.rs

@@ -33682,7 +33682,7 @@ pub mod root {
                    root::nsCharTraits ) ));
     }
     #[test]
-    fn __bindgen_test_layout__bindgen_ty_id_206916_instantiation_97() {
+    fn __bindgen_test_layout__bindgen_ty_id_206919_instantiation_97() {
         assert_eq!(::std::mem::size_of::<u8>() , 1usize , concat ! (
                    "Size of template specialization: " , stringify ! ( u8 )
                    ));
@@ -33691,7 +33691,7 @@ pub mod root {
                    ) ));
     }
     #[test]
-    fn __bindgen_test_layout__bindgen_ty_id_206952_instantiation_98() {
+    fn __bindgen_test_layout__bindgen_ty_id_206955_instantiation_98() {
         assert_eq!(::std::mem::size_of::<u8>() , 1usize , concat ! (
                    "Size of template specialization: " , stringify ! ( u8 )
                    ));

servo/components/style/properties/declaration_block.rs

@@ -12,6 +12,7 @@ use cssparser::{Parser, AtRuleParser, DeclarationParser, Delimiter};
 use error_reporting::ParseErrorReporter;
 use parser::{PARSING_MODE_DEFAULT, ParsingMode, ParserContext, log_css_error};
 use std::fmt;
+use std::slice::Iter;
 use style_traits::ToCss;
 use stylesheets::{CssRuleType, Origin, UrlExtraData};
 use super::*;
@@ -54,6 +55,25 @@ pub struct PropertyDeclarationBlock {
     longhands: LonghandIdSet,
 }
 
+/// Iterator for PropertyDeclaration to be generated from PropertyDeclarationBlock.
+#[derive(Clone)]
+pub struct PropertyDeclarationIterator<'a> {
+    iter: Iter<'a, (PropertyDeclaration, Importance)>,
+}
+
+impl<'a> Iterator for PropertyDeclarationIterator<'a> {
+    type Item = &'a PropertyDeclaration;
+    #[inline]
+    fn next(&mut self) -> Option<&'a PropertyDeclaration> {
+        // we use this function because a closure won't be `Clone`
+        fn get_declaration(dec: &(PropertyDeclaration, Importance))
+            -> &PropertyDeclaration {
+            &dec.0
+        }
+        self.iter.next().map(get_declaration as fn(_) -> _)
+    }
+}
+
 impl fmt::Debug for PropertyDeclarationBlock {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         self.declarations.fmt(f)
@@ -93,6 +113,13 @@ impl PropertyDeclarationBlock {
         &self.declarations
     }
 
+    /// Iterate over only PropertyDeclaration.
+    pub fn declarations_iter(&self) -> PropertyDeclarationIterator {
+        PropertyDeclarationIterator {
+            iter: self.declarations.iter(),
+        }
+    }
+
     /// Returns whether this block contains any declaration with `!important`.
     ///
     /// This is based on the `important_count` counter,
@@ -369,15 +396,10 @@ impl PropertyDeclarationBlock {
                 }
             }
             Ok(shorthand) => {
-                // we use this function because a closure won't be `Clone`
-                fn get_declaration(dec: &(PropertyDeclaration, Importance))
-                    -> &PropertyDeclaration {
-                    &dec.0
-                }
                 if !self.declarations.iter().all(|decl| decl.0.shorthands().contains(&shorthand)) {
                     return Err(fmt::Error)
                 }
-                let iter = self.declarations.iter().map(get_declaration as fn(_) -> _);
+                let iter = self.declarations_iter();
                 match shorthand.get_shorthand_appendable_value(iter) {
                     Some(AppendableValue::Css { css, .. }) => {
                         dest.write_str(css)

servo/components/style/properties/shorthand/font.mako.rs

@@ -122,8 +122,67 @@
             SomeSystem,
             None
         }
+    % endif
+    enum SerializeFor {
+        Normal,
+    % if product == "gecko":
+        Canvas,
+    % endif
+    }
 
-        impl<'a> LonghandsToSerialize<'a> {
+    impl<'a> LonghandsToSerialize<'a> {
+        fn to_css_for<W>(&self,
+                         serialize_for: SerializeFor,
+                         dest: &mut W) -> fmt::Result where W: fmt::Write {
+            % if product == "gecko":
+                match self.check_system() {
+                    CheckSystemResult::AllSystem(sys) => return sys.to_css(dest),
+                    CheckSystemResult::SomeSystem => return Ok(()),
+                    CheckSystemResult::None => ()
+                }
+            % endif
+
+            % if product == "gecko" or data.testing:
+                % for name in gecko_sub_properties:
+                    if self.font_${name} != &font_${name}::get_initial_specified_value() {
+                        return Ok(());
+                    }
+                % endfor
+            % endif
+
+            // In case of serialization for canvas font, we need to drop
+            // initial values of properties other than size and family.
+            % for name in "style variant_caps weight stretch".split():
+                let needs_this_property = match serialize_for {
+                    SerializeFor::Normal => true,
+                % if product == "gecko":
+                    SerializeFor::Canvas =>
+                        self.font_${name} != &font_${name}::get_initial_specified_value(),
+                % endif
+                };
+                if needs_this_property {
+                    self.font_${name}.to_css(dest)?;
+                    dest.write_str(" ")?;
+                }
+            % endfor
+
+            self.font_size.to_css(dest)?;
+
+            match *self.line_height {
+                line_height::SpecifiedValue::Normal => {},
+                _ => {
+                    dest.write_str("/")?;
+                    self.line_height.to_css(dest)?;
+                }
+            }
+
+            dest.write_str(" ")?;
+            self.font_family.to_css(dest)?;
+
+            Ok(())
+        }
+
+        % if product == "gecko":
             /// Check if some or all members are system fonts
             fn check_system(&self) -> CheckSystemResult {
                 let mut sys = None;
@@ -148,47 +207,18 @@
                     CheckSystemResult::None
                 }
             }
-        }
-    % endif
+
+            /// Serialize the shorthand value for canvas font attribute.
+            pub fn to_css_for_canvas<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
+                self.to_css_for(SerializeFor::Canvas, dest)
+            }
+        % endif
+    }
 
     // This may be a bit off, unsure, possibly needs changes
     impl<'a> ToCss for LonghandsToSerialize<'a>  {
         fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
-            % if product == "gecko":
-                match self.check_system() {
-                    CheckSystemResult::AllSystem(sys) => return sys.to_css(dest),
-                    CheckSystemResult::SomeSystem => return Ok(()),
-                    CheckSystemResult::None => ()
-                }
-            % endif
-
-    % if product == "gecko" or data.testing:
-        % for name in gecko_sub_properties:
-            if self.font_${name} != &font_${name}::get_initial_specified_value() {
-                return Ok(());
-            }
-        % endfor
-    % endif
-
-    % for name in "style variant_caps weight stretch".split():
-            self.font_${name}.to_css(dest)?;
-            dest.write_str(" ")?;
-    % endfor
-
-            self.font_size.to_css(dest)?;
-
-            match *self.line_height {
-                line_height::SpecifiedValue::Normal => {},
-                _ => {
-                    dest.write_str("/")?;
-                    self.line_height.to_css(dest)?;
-                }
-            }
-
-            dest.write_str(" ")?;
-            self.font_family.to_css(dest)?;
-
-            Ok(())
+            self.to_css_for(SerializeFor::Normal, dest)
         }
     }
 </%helpers:shorthand>

servo/ports/geckolib/glue.rs

@@ -1434,6 +1434,29 @@ pub extern "C" fn Servo_DeclarationBlock_SerializeOneValue(
     })
 }
 
+#[no_mangle]
+pub extern "C" fn Servo_SerializeFontValueForCanvas(
+    declarations: RawServoDeclarationBlockBorrowed,
+    buffer: *mut nsAString) {
+    use style::properties::shorthands::font;
+
+    read_locked_arc(declarations, |decls: &PropertyDeclarationBlock| {
+        let longhands = match font::LonghandsToSerialize::from_iter(decls.declarations_iter()) {
+            Ok(l) => l,
+            Err(()) => {
+                warn!("Unexpected property!");
+                return;
+            }
+        };
+
+        let mut string = String::new();
+        let rv = longhands.to_css_for_canvas(&mut string);
+        debug_assert!(rv.is_ok());
+
+        write!(unsafe { &mut *buffer }, "{}", string).expect("Failed to copy string");
+    })
+}
+
 #[no_mangle]
 pub extern "C" fn Servo_DeclarationBlock_Count(declarations: RawServoDeclarationBlockBorrowed) -> u32 {
     read_locked_arc(declarations, |decls: &PropertyDeclarationBlock| {