Bug 1674227 - Handle -moz-emoji generic in gfxPlatformFontList. r=jfkthame

And tweak the code so that it doesn't happen next time we add a new
generic font.

Differential Revision: https://phabricator.services.mozilla.com/D95211

gfx/thebes/gfxFontFamilyList.h

@@ -70,24 +70,18 @@ struct FontFamilyName final {
       case StyleGenericFontFamily::MozEmoji:
         MOZ_FALLTHROUGH_ASSERT("Should never appear in a font-family name!");
       case StyleGenericFontFamily::Serif:
-        aFamilyList.AppendLiteral("serif");
-        break;
+        return aFamilyList.AppendLiteral("serif");
       case StyleGenericFontFamily::SansSerif:
-        aFamilyList.AppendLiteral("sans-serif");
-        break;
+        return aFamilyList.AppendLiteral("sans-serif");
       case StyleGenericFontFamily::Monospace:
-        aFamilyList.AppendLiteral("monospace");
-        break;
+        return aFamilyList.AppendLiteral("monospace");
       case StyleGenericFontFamily::Cursive:
-        aFamilyList.AppendLiteral("cursive");
-        break;
+        return aFamilyList.AppendLiteral("cursive");
       case StyleGenericFontFamily::Fantasy:
-        aFamilyList.AppendLiteral("fantasy");
-        break;
-      default:
-        MOZ_ASSERT_UNREACHABLE("Unknown generic font-family!");
-        break;
+        return aFamilyList.AppendLiteral("fantasy");
     }
+    MOZ_ASSERT_UNREACHABLE("Unknown generic font-family!");
+    return aFamilyList.AppendLiteral("serif");
   }
 
   // helper method that converts generic names to the right enum value

gfx/thebes/gfxPlatformFontList.cpp

@@ -2076,29 +2076,26 @@ nsAtom* gfxPlatformFontList::GetLangGroup(nsAtom* aLanguage) {
 
 /* static */ const char* gfxPlatformFontList::GetGenericName(
     StyleGenericFontFamily aGenericType) {
-  static const char kGeneric_serif[] = "serif";
-  static const char kGeneric_sans_serif[] = "sans-serif";
-  static const char kGeneric_monospace[] = "monospace";
-  static const char kGeneric_cursive[] = "cursive";
-  static const char kGeneric_fantasy[] = "fantasy";
-
   // type should be standard generic type at this point
   // map generic type to string
   switch (aGenericType) {
     case StyleGenericFontFamily::Serif:
-      return kGeneric_serif;
+      return "serif";
     case StyleGenericFontFamily::SansSerif:
-      return kGeneric_sans_serif;
+      return "sans-serif";
     case StyleGenericFontFamily::Monospace:
-      return kGeneric_monospace;
+      return "monospace";
     case StyleGenericFontFamily::Cursive:
-      return kGeneric_cursive;
+      return "cursive";
     case StyleGenericFontFamily::Fantasy:
-      return kGeneric_fantasy;
-    default:
-      MOZ_ASSERT_UNREACHABLE("Unknown generic");
-      return nullptr;
+      return "fantasy";
+    case StyleGenericFontFamily::MozEmoji:
+      return "-moz-emoji";
+    case StyleGenericFontFamily::None:
+      break;
   }
+  MOZ_ASSERT_UNREACHABLE("Unknown generic");
+  return nullptr;
 }
 
 void gfxPlatformFontList::InitLoader() {

layout/base/StaticPresData.h

@@ -72,11 +72,12 @@ struct LangGroupFontPrefs {
         return &mDefaultCursiveFont;
       case StyleGenericFontFamily::Fantasy:
         return &mDefaultFantasyFont;
+      case StyleGenericFontFamily::MozEmoji:
+        // This shouldn't appear in font family names.
         break;
-      default:
-        MOZ_ASSERT_UNREACHABLE("invalid font id");
-        return nullptr;
     }
+    MOZ_ASSERT_UNREACHABLE("invalid font id");
+    return nullptr;
   }
 
   nsStaticAtom* mLangGroup;