Bug 1554819 - Ensure fontgroups attached to CanvasRenderingContext2D get reset after a shared-fontlist rebuild. r=jwatt

Differential Revision: https://phabricator.services.mozilla.com/D53264

--HG--
extra : moz-landing-system : lando

dom/canvas/CanvasRenderingContext2D.cpp

@@ -3978,6 +3978,9 @@ gfxFontGroup* CanvasRenderingContext2D::GetCurrentFontStyle() {
         NS_ERROR("Default canvas font is invalid");
       }
     }
+  } else {
+    // The fontgroup needs to check if its cached families/faces are valid.
+    CurrentState().fontGroup->CheckForUpdatedPlatformList();
   }
 
   return CurrentState().fontGroup;

gfx/thebes/gfxPlatformFontList.cpp

@@ -2319,5 +2319,9 @@ void gfxPlatformFontList::InitOtherFamilyNames(uint32_t aGeneration,
   InitOtherFamilyNames(aDefer);
 }
 
+uint32_t gfxPlatformFontList::GetGeneration() const {
+  return SharedFontList() ? SharedFontList()->GetGeneration() : 0;
+}
+
 #undef LOG
 #undef LOG_ENABLED

gfx/thebes/gfxPlatformFontList.h

@@ -444,6 +444,14 @@ class gfxPlatformFontList : public gfxFontInfoLoader {
     return mCodepointsWithNoFonts.test(aCh);
   }
 
+  // If using the shared font list, returns a generation count that is
+  // incremented if/when the platform list is reinitialized (e.g. because
+  // fonts are installed/removed while the browser is running), such that
+  // existing references to shared font family or face objects and character
+  // maps will no longer be valid.
+  // (The legacy (non-shared) list just returns 0 here.)
+  uint32_t GetGeneration() const;
+
  protected:
   friend class mozilla::fontlist::FontList;
   friend class InitOtherFamilyNamesForStylo;

gfx/thebes/gfxTextRun.cpp

@@ -1734,6 +1734,8 @@ void gfxFontGroup::BuildFontList() {
       AddFamilyToFontList(f.mFamily.mUnshared, f.mGeneric);
     }
   }
+
+  mFontListGeneration = pfl->GetGeneration();
 }
 
 void gfxFontGroup::AddPlatformFont(const nsACString& aName, bool aQuotedName,

gfx/thebes/gfxTextRun.h

@@ -1049,6 +1049,17 @@ class gfxFontGroup final : public gfxTextRunFactory {
       int32_t aAppUnitsPerDevPixel, mozilla::gfx::ShapedTextFlags aFlags,
       LazyReferenceDrawTargetGetter& aRefDrawTargetGetter);
 
+  void CheckForUpdatedPlatformList() {
+    auto* pfl = gfxPlatformFontList::PlatformFontList();
+    if (mFontListGeneration != pfl->GetGeneration()) {
+      // Forget cached fonts that may no longer be valid.
+      mLastPrefFamily = FontFamily();
+      mLastPrefFont = nullptr;
+      mFonts.Clear();
+      BuildFontList();
+    }
+  }
+
  protected:
   friend class mozilla::PostTraversalTask;
 
@@ -1357,6 +1368,9 @@ class gfxFontGroup final : public gfxTextRunFactory {
                       // download to complete (or fallback
                       // timer to fire)
 
+  uint32_t mFontListGeneration = 0;  // platform font list generation for this
+                                     // fontgroup
+
   /**
    * Textrun creation short-cuts for special cases where we don't need to
    * call a font shaper to generate glyphs.