Bug 1315752 - Avoid using LookupLocalFont to find the Osaka-Mono face in InitSingleFaceList, so we don't risk triggering a font-download prompt. r=mstange

The issue is that with Osaka becoming a downloadable asset rather than a
    universally pre-installed font, it's possible for a user's system to be in
    a state where the Osaka-Regular face is present (and therefore the Osaka
    family shows up in the main font family list), but Osaka-Mono has still not
    been downloaded. Until recently, I wasn't aware that the family could be in
    that partially-installed state, but apparently it does happen (perhaps
    depending on how the download was originally triggered).

    The download prompt then occurs when we use LookupLocalFont() to find the
    Osaka-Mono face, because that calls CGFontCreateWithFontName, which is
    aware of the downloadable font assets; so when it is asked for Osaka-Mono,
    and sees that it hasn't been downloaded, it offers to help out.

    We tried to avoid this by checking for the presence of the Osaka family
    before calling LookupLocalFont(), and that solved things for most users
    (where the Osaka family was either fully installed or not installed at
    all), but it fails in the case where the Regular face is present but Mono
    isn't.

    So this patch works around that by avoiding LookupLocalFont (and therefore
    CGFontCreateWithFontName) altogether, and instead searching the faces
    actually present in the main Osaka family. If Osaka-Mono is installed, it
    will be found there and we can then duplicate its font entry and create the
    separate Osaka-Mono family; and if not, we safely (and silently) ignore it.

gfx/thebes/gfxMacPlatformFontList.mm

@@ -829,43 +829,70 @@ gfxMacPlatformFontList::InitSingleFaceList()
     AutoTArray<nsString, 10> singleFaceFonts;
     gfxFontUtils::GetPrefsFontList("font.single-face-list", singleFaceFonts);
 
-    uint32_t numFonts = singleFaceFonts.Length();
-    for (uint32_t i = 0; i < numFonts; i++) {
+    for (const auto& singleFaceFamily : singleFaceFonts) {
         LOG_FONTLIST(("(fontlist-singleface) face name: %s\n",
-                      NS_ConvertUTF16toUTF8(singleFaceFonts[i]).get()));
-        nsAutoString familyName(singleFaceFonts[i]);
+                      NS_ConvertUTF16toUTF8(singleFaceFamily).get()));
+        // Each entry in the "single face families" list is expected to be a
+        // colon-separated pair of FaceName:Family,
+        // where FaceName is the individual face name (psname) of a font
+        // that should be exposed as a separate family name,
+        // and Family is the standard family to which that face belongs.
+        // The only such face listed by default is
+        //    Osaka-Mono:Osaka
+        nsAutoString familyName(singleFaceFamily);
         auto colon = familyName.FindChar(':');
-        if (colon != kNotFound) {
-            nsAutoString key(Substring(familyName, colon + 1));
-            ToLowerCase(key);
-            if (!mFontFamilies.GetWeak(key)) {
-                continue;
-            }
-            familyName.Truncate(colon);
+        if (colon == kNotFound) {
+            continue;
         }
-        gfxFontEntry *fontEntry = LookupLocalFont(familyName,
-                                                  400, 0,
-                                                  NS_FONT_STYLE_NORMAL);
-        if (fontEntry) {
-            nsAutoString key;
-            GenerateFontListKey(familyName, key);
-            LOG_FONTLIST(("(fontlist-singleface) family name: %s, key: %s\n",
+
+        // Look for the parent family in the main font family list,
+        // and ensure we have loaded its list of available faces.
+        nsAutoString key(Substring(familyName, colon + 1));
+        ToLowerCase(key);
+        gfxFontFamily* family = mFontFamilies.GetWeak(key);
+        if (!family) {
+            continue;
+        }
+        family->FindStyleVariations();
+
+        // Truncate the entry from prefs at the colon, so now it is just the
+        // desired single-face-family name.
+        familyName.Truncate(colon);
+
+        // Look through the family's faces to see if this one is present.
+        const gfxFontEntry* fe = nullptr;
+        for (const auto& face : family->GetFontList()) {
+            if (face->Name().Equals(familyName)) {
+                fe = face;
+                break;
+            }
+        }
+        if (!fe) {
+            continue;
+        }
+
+        // We found the correct face, so create the single-face family record.
+        GenerateFontListKey(familyName, key);
+        LOG_FONTLIST(("(fontlist-singleface) family name: %s, key: %s\n",
+                      NS_ConvertUTF16toUTF8(familyName).get(),
+                      NS_ConvertUTF16toUTF8(key).get()));
+
+        // add only if doesn't exist already
+        if (!mFontFamilies.GetWeak(key)) {
+            RefPtr<gfxFontFamily> familyEntry =
+                new gfxSingleFaceMacFontFamily(familyName);
+            // We need a separate font entry, because its family name will
+            // differ from the one we found in the main list.
+            MacOSFontEntry* fontEntry =
+                new MacOSFontEntry(fe->Name(), fe->mWeight, true,
+                                   static_cast<const MacOSFontEntry*>(fe)->
+                                       mSizeHint);
+            familyEntry->AddFontEntry(fontEntry);
+            familyEntry->SetHasStyles(true);
+            mFontFamilies.Put(key, familyEntry);
+            LOG_FONTLIST(("(fontlist-singleface) added new family\n",
                           NS_ConvertUTF16toUTF8(familyName).get(),
                           NS_ConvertUTF16toUTF8(key).get()));
-
-            // add only if doesn't exist already
-            if (!mFontFamilies.GetWeak(key)) {
-                RefPtr<gfxFontFamily> familyEntry =
-                    new gfxSingleFaceMacFontFamily(familyName);
-                // LookupLocalFont sets this, need to clear
-                fontEntry->mIsLocalUserFont = false;
-                familyEntry->AddFontEntry(fontEntry);
-                familyEntry->SetHasStyles(true);
-                mFontFamilies.Put(key, familyEntry);
-                LOG_FONTLIST(("(fontlist-singleface) added new family\n",
-                              NS_ConvertUTF16toUTF8(familyName).get(),
-                              NS_ConvertUTF16toUTF8(key).get()));
-            }
         }
     }
 }