Bug 1331737 - Expose a pref to control the validation of OpenType Layout tables, so that Nightly/Aurora users can choose to bypass validation (like we do on Beta/Release) if they really want out-of-spec fonts to be loaded. r=jrmuizel

gfx/thebes/gfxPrefs.h

@@ -383,6 +383,7 @@ private:
   DECL_GFX_PREF(Once, "gfx.direct2d.force-enabled",            Direct2DForceEnabled, bool, false);
   DECL_GFX_PREF(Live, "gfx.direct3d11.reuse-decoder-device",   Direct3D11ReuseDecoderDevice, int32_t, -1);
   DECL_GFX_PREF(Live, "gfx.direct3d11.allow-intel-mutex",      Direct3D11AllowIntelMutex, bool, true);
+  DECL_GFX_PREF(Live, "gfx.downloadable_fonts.otl_validation", ValidateOTLTables, bool, true);
   DECL_GFX_PREF(Live, "gfx.draw-color-bars",                   CompositorDrawColorBars, bool, false);
   DECL_GFX_PREF(Once, "gfx.e10s.hide-plugins-for-scroll",      HidePluginsForScroll, bool, true);
   DECL_GFX_PREF(Live, "gfx.layerscope.enabled",                LayerScopeEnabled, bool, false);

gfx/thebes/gfxUserFontSet.cpp

@@ -7,6 +7,7 @@
 
 #include "gfxUserFontSet.h"
 #include "gfxPlatform.h"
+#include "gfxPrefs.h"
 #include "nsContentPolicyUtils.h"
 #include "nsUnicharUtils.h"
 #include "nsNetUtil.h"
@@ -176,17 +177,19 @@ gfxUserFontEntry::CreateFontInstance(const gfxFontStyle* aFontStyle, bool aNeeds
 class gfxOTSContext : public ots::OTSContext {
 public:
     explicit gfxOTSContext(gfxUserFontEntry* aUserFontEntry)
-        : mUserFontEntry(aUserFontEntry) {}
+        : mUserFontEntry(aUserFontEntry)
+    {
+        // Whether to apply OTS validation to OpenType Layout tables
+        mCheckOTLTables = gfxPrefs::ValidateOTLTables();
+    }
 
     virtual ots::TableAction GetTableAction(uint32_t aTag) override {
-        // Preserve Graphite, color glyph and SVG tables
-        if (
-#ifdef RELEASE_OR_BETA // For Beta/Release, also allow OT Layout tables through
-                     // unchecked, and rely on harfbuzz to handle them safely.
-            aTag == TRUETYPE_TAG('G', 'D', 'E', 'F') ||
-            aTag == TRUETYPE_TAG('G', 'P', 'O', 'S') ||
-            aTag == TRUETYPE_TAG('G', 'S', 'U', 'B') ||
-#endif
+        // Preserve Graphite, color glyph and SVG tables,
+        // and possibly OTL tables (depending on pref)
+        if ((!mCheckOTLTables &&
+             (aTag == TRUETYPE_TAG('G', 'D', 'E', 'F') ||
+              aTag == TRUETYPE_TAG('G', 'P', 'O', 'S') ||
+              aTag == TRUETYPE_TAG('G', 'S', 'U', 'B'))) ||
             aTag == TRUETYPE_TAG('S', 'i', 'l', 'f') ||
             aTag == TRUETYPE_TAG('S', 'i', 'l', 'l') ||
             aTag == TRUETYPE_TAG('G', 'l', 'o', 'c') ||
@@ -225,6 +228,7 @@ public:
 private:
     gfxUserFontEntry* mUserFontEntry;
     nsTHashtable<nsCStringHashKey> mWarningsIssued;
+    bool mCheckOTLTables;
 };
 
 // Call the OTS library to sanitize an sfnt before attempting to use it.

modules/libpref/init/all.js

@@ -742,6 +742,13 @@ pref("gfx.downloadable_fonts.disable_cache", false);
 
 pref("gfx.downloadable_fonts.woff2.enabled", true);
 
+// Whether OTS validation should be applied to OpenType Layout (OTL) tables
+#ifdef RELEASE_OR_BETA
+pref("gfx.downloadable_fonts.otl_validation", false);
+#else
+pref("gfx.downloadable_fonts.otl_validation", true);
+#endif
+
 #ifdef ANDROID
 pref("gfx.bundled_fonts.enabled", true);
 pref("gfx.bundled_fonts.force-enabled", false);