Bug 1854090 - Omit psnames of fonts with family-name *.tmp from src:l…

…ocal() lookups on Windows. r=jwatt, a=dsmith

This is a sad hack, but aims to work around the issue that some
PDF-related software (Acrobat is suspected but not currently confirmed)
is potentially polluting the global font collection with re-encoded
subsets of standard fonts like Arial, but does not munge the psname;
these can then be returned by src:local(...) lookups, which results in
garbled or missing text.

In principle, if such fonts are "installed", Firefox is not wrong to use
them; it's just a badly-configured system. But given that it seems to be
caused by some PDF-handling software, without the user's knowledge, it
seems worth trying to avoid the problem. Simply skipping the psname of
any font with family-name *.tmp is highly unlikely to adversely affect
any real-world content.

Differential Revision: https://phabricator.services.mozilla.com/D191639

gfx/thebes/gfxDWriteFontList.cpp

@@ -1499,11 +1499,18 @@ void gfxDWriteFontList::ReadFaceNamesForFamily(
       }
 
       nsAutoCString psname, fullname;
-      if (NS_SUCCEEDED(gfxFontUtils::ReadCanonicalName(
-              data, size, gfxFontUtils::NAME_ID_POSTSCRIPT, psname))) {
-        ToLowerCase(psname);
-        mLocalNameTable.InsertOrUpdate(
-            psname, fontlist::LocalFaceRec::InitData(key, i));
+      // Bug 1854090: don't load PSname if the family name ends with ".tmp",
+      // as some PDF-related software appears to pollute the font collection
+      // with spurious re-encoded versions of standard fonts like Arial, fails
+      // to alter the PSname, and thus can result in garbled rendering because
+      // the wrong resource may be found via src:local(...).
+      if (!StringEndsWith(key, ".tmp"_ns)) {
+        if (NS_SUCCEEDED(gfxFontUtils::ReadCanonicalName(
+                data, size, gfxFontUtils::NAME_ID_POSTSCRIPT, psname))) {
+          ToLowerCase(psname);
+          mLocalNameTable.InsertOrUpdate(
+              psname, fontlist::LocalFaceRec::InitData(key, i));
+        }
       }
       if (NS_SUCCEEDED(gfxFontUtils::ReadCanonicalName(
               data, size, gfxFontUtils::NAME_ID_FULL, fullname))) {