stylo: Support system colors

MozReview-Commit-ID: HUfTdcMRoEx

components/style/properties/longhand/color.mako.rs

@@ -6,6 +6,8 @@
 
 <% data.new_style_struct("Color", inherited=True) %>
 
+<% from data import to_rust_ident %>
+
 <%helpers:longhand name="color" need_clone="True" animatable="True"
                    spec="https://drafts.csswg.org/css-color/#color">
     use cssparser::RGBA;
@@ -53,4 +55,91 @@
     pub fn parse(context: &ParserContext, input: &mut Parser) -> Result<SpecifiedValue, ()> {
         CSSColor::parse(context, input).map(SpecifiedValue)
     }
+
+    // FIXME(#15973): Add servo support for system colors
+    % if product == "gecko":
+        <%
+            # These are actually parsed. See nsCSSProps::kColorKTable
+            system_colors = """activeborder activecaption appworkspace background buttonface
+                               buttonhighlight buttonshadow buttontext captiontext graytext highlight
+                               highlighttext inactiveborder inactivecaption inactivecaptiontext
+                               infobackground infotext menu menutext scrollbar threeddarkshadow
+                               threedface threedhighlight threedlightshadow threedshadow window
+                               windowframe windowtext -moz-buttondefault -moz-buttonhoverface
+                               -moz-buttonhovertext -moz-cellhighlight -moz-cellhighlighttext
+                               -moz-eventreerow -moz-field -moz-fieldtext -moz-dialog -moz-dialogtext
+                               -moz-dragtargetzone -moz-gtk-info-bar-text -moz-html-cellhighlight
+                               -moz-html-cellhighlighttext -moz-mac-buttonactivetext
+                               -moz-mac-chrome-active -moz-mac-chrome-inactive
+                               -moz-mac-defaultbuttontext -moz-mac-focusring -moz-mac-menuselect
+                               -moz-mac-menushadow -moz-mac-menutextdisable -moz-mac-menutextselect
+                               -moz-mac-disabledtoolbartext -moz-mac-secondaryhighlight
+                               -moz-menuhover -moz-menuhovertext -moz-menubartext -moz-menubarhovertext
+                               -moz-oddtreerow -moz-win-mediatext -moz-win-communicationstext
+                               -moz-nativehyperlinktext -moz-comboboxtext -moz-combobox""".split()
+
+            # These are not parsed but must be serialized
+            # They are only ever set directly by Gecko
+            extra_colors = """WindowBackground WindowForeground WidgetBackground WidgetForeground
+                              WidgetSelectBackground WidgetSelectForeground Widget3DHighlight Widget3DShadow
+                              TextBackground TextForeground TextSelectBackground TextSelectForeground
+                              TextSelectForegroundCustom TextSelectBackgroundDisabled TextSelectBackgroundAttention
+                              TextHighlightBackground TextHighlightForeground IMERawInputBackground
+                              IMERawInputForeground IMERawInputUnderline IMESelectedRawTextBackground
+                              IMESelectedRawTextForeground IMESelectedRawTextUnderline
+                              IMEConvertedTextBackground IMEConvertedTextForeground IMEConvertedTextUnderline
+                              IMESelectedConvertedTextBackground IMESelectedConvertedTextForeground
+                              IMESelectedConvertedTextUnderline SpellCheckerUnderline""".split()
+        %>
+        use gecko_bindings::bindings::Gecko_GetLookAndFeelSystemColor;
+        use gecko_bindings::structs::root::mozilla::LookAndFeel_ColorID;
+        pub type SystemColor = LookAndFeel_ColorID;
+
+        impl ToCss for SystemColor {
+            fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
+                let s = match *self {
+                    % for color in system_colors + extra_colors:
+                        LookAndFeel_ColorID::eColorID_${to_rust_ident(color)} => "${color}",
+                    % endfor
+                    LookAndFeel_ColorID::eColorID_LAST_COLOR => unreachable!(),
+                };
+                dest.write_str(s)
+            }
+        }
+
+        impl ToComputedValue for SystemColor {
+            type ComputedValue = u32; // nscolor
+            #[inline]
+            fn to_computed_value(&self, cx: &Context) -> Self::ComputedValue {
+                unsafe {
+                    Gecko_GetLookAndFeelSystemColor(*self as i32,
+                                                    &*cx.device.pres_context)
+                }
+            }
+
+            #[inline]
+            fn from_computed_value(_: &Self::ComputedValue) -> Self {
+                unreachable!()
+            }
+        }
+
+        impl SystemColor {
+            pub fn parse(input: &mut Parser) -> Result<Self, ()> {
+                use std::ascii::AsciiExt;
+                static PARSE_ARRAY: &'static [(&'static str, SystemColor); ${len(system_colors)}] = &[
+                    % for color in system_colors:
+                        ("${color}", LookAndFeel_ColorID::eColorID_${to_rust_ident(color)}),
+                    % endfor
+                ];
+
+                let ident = input.expect_ident()?;
+                for &(name, color) in PARSE_ARRAY.iter() {
+                    if name.eq_ignore_ascii_case(&ident) {
+                        return Ok(color)
+                    }
+                }
+                Err(())
+            }
+        }
+    % endif
 </%helpers:longhand>