Bug 1776556 - Restore Windows' accent-color / system-color behavior for now. r=mstange

This basically pref-gates some of the accent-color changes that landed before
the soft-freeze to match current release behavior, at least for now.

In the future we might want to reconsider turning these on, but at the very
least we should figure out a good story for the grey-ish accent colors, see the
comments in the pref definitions.

The only tricky bit is the use-theme-accent pref handling. I made it specific
to the non-native-theme again so that AccentColor and NNT kept behaving
consistently, but AccentColor in the browser chrome used the real accent color.

Differential Revision: https://phabricator.services.mozilla.com/D150339

modules/libpref/init/StaticPrefList.yaml

@@ -13589,10 +13589,21 @@
   value: false
   mirror: always
 
-# Whether we should use the default accent color or the theme-provided one.
-- name: widget.use-theme-accent
+# Whether we should use the default accent color or the theme-provided one for
+# content (e.g. for form controls and CSS system colors).
+#
+# Turned off on Windows, for now (we always use the default blue-ish
+# accent-color there). We might want to turn this on there, though it's worth
+# thinking on what the behavior should be for grey-ish accent colors (which are
+# a thing on Windows and can cause confusion with things like disabled form
+# controls). Maybe it's just fine.
+- name: widget.non-native-theme.use-theme-accent
   type: RelaxedAtomicBool
+#ifdef XP_WIN
+  value: false
+#else
   value: true
+#endif
   mirror: always
 
 # Whether we should try to use WebRender to render widgets.
@@ -13856,6 +13867,15 @@
   value: true
   mirror: always
 
+# Whether we use the accent color for highlight as some other UWP apps do.
+#
+# false for now since it can cause some contrast-with-background issues
+# specially with grey accents, see bug 1776588.
+- name: widget.windows.uwp-system-colors.highlight-accent
+  type: bool
+  value: false
+  mirror: always
+
 - name: widget.windows.window_occlusion_tracking_display_state.enabled
   type: bool
   value: false

widget/ThemeColors.cpp

@@ -84,10 +84,12 @@ struct ColorPalette {
 };
 
 static nscolor GetAccentColor(bool aBackground, ColorScheme aScheme) {
+  auto useStandins = LookAndFeel::UseStandins(
+      !StaticPrefs::widget_non_native_theme_use_theme_accent());
   return ColorPalette::EnsureOpaque(
       LookAndFeel::Color(aBackground ? LookAndFeel::ColorID::Accentcolor
                                      : LookAndFeel::ColorID::Accentcolortext,
-                         aScheme, LookAndFeel::UseStandins::No));
+                         aScheme, useStandins));
 }
 
 static ColorPalette sDefaultLightPalette = ColorPalette::Default();

widget/android/nsLookAndFeel.cpp

@@ -112,7 +112,8 @@ nsresult nsLookAndFeel::NativeGetColor(ColorID aID, ColorScheme aColorScheme,
   // XXX we'll want to use context.obtainStyledAttributes on the java side to
   // get all of these; see TextView.java for a good example.
   auto UseNativeAccent = [this] {
-    return mSystemColors.colorAccent && StaticPrefs::widget_use_theme_accent();
+    return mSystemColors.colorAccent &&
+           StaticPrefs::widget_non_native_theme_use_theme_accent();
   };
 
   switch (aID) {

widget/nsXPLookAndFeel.cpp

@@ -456,7 +456,15 @@ static constexpr struct {
       widget::ThemeChangeKind::MediaQueriesOnly;
 } kMediaQueryPrefs[] = {
     {"browser.display.windows.native_menus"_ns},
-    {"widget.use-theme-accent"_ns, widget::ThemeChangeKind::Style},
+    // Affects whether standins are used for the accent color.
+    {"widget.non-native-theme.use-theme-accent"_ns,
+     widget::ThemeChangeKind::Style},
+    // These two affect system colors on Windows.
+    {"widget.windows.uwp-system-colors.enabled"_ns,
+     widget::ThemeChangeKind::Style},
+    // These two affect system colors on Windows.
+    {"widget.windows.uwp-system-colors.highlight-accent"_ns,
+     widget::ThemeChangeKind::Style},
     // Affects env().
     {"layout.css.prefers-color-scheme.content-override"_ns,
      widget::ThemeChangeKind::Style},
@@ -907,14 +915,7 @@ nsresult nsXPLookAndFeel::GetColorValue(ColorID aID, ColorScheme aScheme,
 Maybe<nscolor> nsXPLookAndFeel::GetUncachedColor(ColorID aID,
                                                  ColorScheme aScheme,
                                                  UseStandins aUseStandins) {
-  const bool useStandins = [&] {
-    if (aUseStandins == UseStandins::Yes) {
-      return true;
-    }
-    return !StaticPrefs::widget_use_theme_accent() &&
-           (aID == ColorID::Accentcolor || aID == ColorID::Accentcolortext);
-  }();
-  if (useStandins) {
+  if (aUseStandins == UseStandins::Yes) {
     return Some(GetStandinForNativeColor(aID, aScheme));
   }
   nscolor r;
@@ -1176,10 +1177,18 @@ static constexpr std::bitset<size_t(ColorID::End)> sNonNativeThemeStandinColors{
 static bool ShouldUseStandinsForNativeColorForNonNativeTheme(
     const dom::Document& aDoc, LookAndFeel::ColorID aColor,
     const PreferenceSheet::Prefs& aPrefs) {
-  if (!sNonNativeThemeStandinColors[size_t(aColor)]) {
-    return false;
-  }
-  return aDoc.ShouldAvoidNativeTheme() &&
+  const bool shouldUseStandinsForColor = [&] {
+    if (sNonNativeThemeStandinColors[size_t(aColor)]) {
+      return true;
+    }
+    // There are platforms where we want the content-exposed accent color to be
+    // the windows blue rather than the system accent color, for now.
+    return StaticPrefs::widget_non_native_theme_use_theme_accent() &&
+           (aColor == LookAndFeel::ColorID::Accentcolor ||
+            aColor == LookAndFeel::ColorID::Accentcolortext);
+  }();
+
+  return shouldUseStandinsForColor && aDoc.ShouldAvoidNativeTheme() &&
          !aPrefs.NonNativeThemeShouldBeHighContrast();
 }
 

widget/windows/WindowsUIUtils.cpp

@@ -436,15 +436,24 @@ Maybe<nscolor> WindowsUIUtils::GetSystemColor(ColorScheme aScheme,
 
   // https://docs.microsoft.com/en-us/windows/apps/design/style/color
   // Is a useful resource to see which values have decent contrast.
-  if (aSysColor == COLOR_HIGHLIGHT) {
-    int tone = aScheme == ColorScheme::Light ? 0 : -1;
-    if (auto c = GetAccentColor(tone)) {
-      return c;
+  if (StaticPrefs::widget_windows_uwp_system_colors_highlight_accent()) {
+    if (aSysColor == COLOR_HIGHLIGHT) {
+      int tone = aScheme == ColorScheme::Light ? 0 : -1;
+      if (auto c = GetAccentColor(tone)) {
+        return c;
+      }
+    }
+    if (aSysColor == COLOR_HIGHLIGHTTEXT && GetAccentColor()) {
+      return Some(NS_RGBA(255, 255, 255, 255));
     }
   }
-  if (aSysColor == COLOR_HIGHLIGHTTEXT && GetAccentColor()) {
-    return Some(NS_RGBA(255, 255, 255, 255));
+
+  if (aScheme == ColorScheme::Dark) {
+    // There are no explicitly dark colors in UWP, other than the highlight
+    // colors above.
+    return Nothing();
   }
+
   auto knownType = [&]() -> Maybe<UIElementType> {
 #  define MAP(_win32, _uwp) \
     case COLOR_##_win32:    \