Bug 1759686 - patch 4 - Extend ServoCSSParser::ParseFontShorthandForMatching to (optionally) return font size in addition to family/style. r=emilio

When running in a Worker, the canvas2d SetFontInternal method can't call GetFontStyleForServo
because it doesn't have a canvasElement or presShell to pass. But we can use the method
ServoCSSParser::ParseFontShorthandForMatching to parse the canvas 'font' property, if we
extend it so as to also return the size from the font shorthand.

(This is incomplete by itself; Emilio's following patch fixes it up, so the intention is to land them together.)

Depends on D144186

Differential Revision: https://phabricator.services.mozilla.com/D144187

layout/style/ServoCSSParser.cpp

@@ -59,9 +59,12 @@ bool ServoCSSParser::ParseTransformIntoMatrix(const nsACString& aValue,
 /* static */
 bool ServoCSSParser::ParseFontShorthandForMatching(
     const nsACString& aValue, URLExtraData* aUrl, StyleFontFamilyList& aList,
-    StyleComputedFontStyleDescriptor& aStyle, float& aStretch, float& aWeight) {
+    StyleComputedFontStyleDescriptor& aStyle, float& aStretch, float& aWeight,
+    float* aSize) {
+  float dummySize;
   return Servo_ParseFontShorthandForMatching(&aValue, aUrl, &aList, &aStyle,
-                                             &aStretch, &aWeight);
+                                             &aStretch, &aWeight,
+                                             aSize ? aSize : &dummySize);
 }
 
 /* static */

layout/style/ServoCSSParser.h

@@ -119,12 +119,13 @@ class ServoCSSParser {
    * @param aStyle The parsed FontStyle. (output)
    * @param aStretch The parsed FontStretch. (output)
    * @param aWeight The parsed FontWeight. (output)
+   * @param aSize If non-null, returns the parsed font size. (output)
    * @return Whether the value was successfully parsed.
    */
   static bool ParseFontShorthandForMatching(
       const nsACString& aValue, URLExtraData* aUrl, StyleFontFamilyList& aList,
-      StyleComputedFontStyleDescriptor& aStyle, float& aStretch,
-      float& aWeight);
+      StyleComputedFontStyleDescriptor& aStyle, float& aStretch, float& aWeight,
+      float* aSize = nullptr);
 
   /**
    * Get a URLExtraData from a document.

servo/ports/geckolib/glue.rs

@@ -139,6 +139,7 @@ use style::values::animated::{Animate, Procedure, ToAnimatedZero};
 use style::values::computed::font::{FontFamily, FontFamilyList, GenericFontFamily};
 use style::values::computed::{self, Context, ToComputedValue};
 use style::values::distance::ComputeSquaredDistance;
+use style::values::specified::FontSizeKeyword;
 use style::values::specified::gecko::IntersectionObserverRootMargin;
 use style::values::specified::source_size_list::SourceSizeList;
 use style::values::{specified, AtomIdent, CustomIdent, KeyframesName};
@@ -6964,13 +6965,15 @@ pub unsafe extern "C" fn Servo_ParseFontShorthandForMatching(
     style: &mut ComputedFontStyleDescriptor,
     stretch: &mut f32,
     weight: &mut f32,
+    size: &mut f32,
 ) -> bool {
     use style::properties::shorthands::font;
     use style::values::computed::font::FontWeight as ComputedFontWeight;
     use style::values::generics::font::FontStyle as GenericFontStyle;
     use style::values::specified::font::{
-        FontFamily, FontStretch, FontStyle, FontWeight, SpecifiedFontStyle,
+        FontFamily, FontSize, FontStretch, FontStyle, FontWeight, SpecifiedFontStyle,
     };
+    use style::values::specified::LengthPercentage;
 
     let string = value.as_str_unchecked();
     let mut input = ParserInput::new(&string);
@@ -7026,6 +7029,47 @@ pub unsafe extern "C" fn Servo_ParseFontShorthandForMatching(
         FontWeight::System(_) => return false,
     };
 
+    // XXX This is unfinished; see values::specified::FontSize::ToComputedValue
+    // for a more complete implementation (but we can't use it as-is).
+    *size = match font.font_size {
+        FontSize::Length(lp) => {
+            match lp {
+                LengthPercentage::Length(len) => {
+                    if let Ok(len) = len.to_computed_pixel_length_without_context() {
+                        len
+                    } else {
+                        return false;
+                    }
+                },
+                LengthPercentage::Percentage(_) => return false,
+                // XXX We should support calc() here.
+                LengthPercentage::Calc(_) => return false,
+            }
+        },
+        // Map absolute-size keywords to sizes.
+        // XXX This doesn't account for language- and generic-based sizing
+        // differences.
+        // XXX Chrome resolves these differently in offscreen canvas; need to
+        // check whether that's a bug or is required behavior for some reason.
+        FontSize::Keyword(info) => {
+            match info.kw {
+                FontSizeKeyword::XXSmall => 9.0,
+                FontSizeKeyword::XSmall => 10.0,
+                FontSizeKeyword::Small => 13.0,
+                FontSizeKeyword::Medium => 16.0,
+                FontSizeKeyword::Large => 18.0,
+                FontSizeKeyword::XLarge => 24.0,
+                FontSizeKeyword::XXLarge => 32.0,
+                FontSizeKeyword::XXXLarge => 48.0,
+                FontSizeKeyword::None => unreachable!(),
+            }
+        }
+        // smaller, larger not currently supported
+        FontSize::Smaller => return false,
+        FontSize::Larger => return false,
+        FontSize::System(_) => return false,
+    };
+
     true
 }