Bug 991983 - Emit absolute paths for UnifiedSources. r=gps

This helps upcoming changes, and relieves backends from path resolution.
This has the side effect of chaning the order of some unified sources,
which consequently breaks nsTextFormatter because it declares snprintf
methods after nsStringAPI #defines it.

python/mozbuild/mozbuild/frontend/emitter.py

@@ -779,6 +779,9 @@ class TreeMetadataEmitter(LoggingMixin):
             # Now sort the files to let groupby work.
             sorted_files = sorted(context[variable], key=canonical_suffix_for_file)
             for canonical_suffix, files in itertools.groupby(sorted_files, canonical_suffix_for_file):
+                if variable.startswith('UNIFIED_'):
+                    files = [mozpath.normpath(mozpath.join(context.srcdir, f))
+                             for f in files]
                 arglist = [context, list(files), canonical_suffix]
                 if variable.startswith('UNIFIED_') and 'FILES_PER_UNIFIED_FILE' in context:
                     arglist.append(context['FILES_PER_UNIFIED_FILE'])

python/mozbuild/mozbuild/test/frontend/test_emitter.py

@@ -818,7 +818,9 @@ class TestEmitterBasic(unittest.TestCase):
         }
         for suffix, files in expected.items():
             sources = suffix_map[suffix]
-            self.assertEqual(sources.files, files)
+            self.assertEqual(
+                sources.files,
+                [mozpath.join(reader.config.topsrcdir, f) for f in files])
             self.assertTrue(sources.have_unified_mapping)
 
     def test_unified_sources_non_unified(self):
@@ -840,7 +842,9 @@ class TestEmitterBasic(unittest.TestCase):
         }
         for suffix, files in expected.items():
             sources = suffix_map[suffix]
-            self.assertEqual(sources.files, files)
+            self.assertEqual(
+                sources.files,
+                [mozpath.join(reader.config.topsrcdir, f) for f in files])
             self.assertFalse(sources.have_unified_mapping)
 
     def test_dist_files(self):

xpcom/glue/nsStringAPI.cpp

@@ -1308,3 +1308,5 @@ ParseString(const nsACString& aSource, char aDelimiter,
 
   return true;
 }
+
+#undef snprintf