💼 Disable dx --incremental for libraries with only 1 .java file

build/android/gyp/dex.py

 #!/usr/bin/env python
 #
 # Copyright 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import json
 import logging
 import optparse
 import os
@@ skipping 84 matching lines @@
 
 
 def _DexWasEmpty(paths, changes):
   for path in paths:
     if any(p.endswith('.class')
            for p in changes.old_metadata.IterSubpaths(path)):
       return False
   return True
 
 
+def _IterAllClassFiles(changes):
+  for path in changes.IterAllPaths():
+    for subpath in changes.IterAllSubpaths(path):
+      if subpath.endswith('.class'):
+        yield path
+
+
+def _MightHitDxBug(changes):
+  # We've seen dx --incremental fail for small libraries. It's unlikely a
+  # speed-up anyways in this case.
+  num_classes = sum(1 for x in _IterAllClassFiles(changes))
+  if num_classes < 10:
+    return True
+
+  # We've also been able to consistently produce a failure by adding an empty
+  # line to the top of the first .java file of a library.
+  # https://crbug.com/617935
+  first_file = next(_IterAllClassFiles(changes))
+  for path in changes.IterChangedPaths():
+    for subpath in changes.IterChangedSubpaths(path):
+      if first_file == subpath:
+        return True
+  return False
+
+
 def _RunDx(changes, options, dex_cmd, paths):
   with build_utils.TempDir() as classes_temp_dir:
     # --multi-dex is incompatible with --incremental.
     if options.multi_dex:
       dex_cmd.append('--main-dex-list=%s' % options.main_dex_list_path)
     else:
-      # Use --incremental when .class files are added or modified (never when
-      # removed).
       # --incremental tells dx to merge all newly dex'ed .class files with
       # what that already exist in the output dex file (existing classes are
       # replaced).
-      if options.incremental and changes.AddedOrModifiedOnly():
+      # Use --incremental when .class files are added or modified, but not when
+      # any are removed (since it won't know to remove them).
+      if (options.incremental
+          and not _MightHitDxBug(changes)
+          and changes.AddedOrModifiedOnly()):
         changed_inputs = set(changes.IterChangedPaths())
         changed_paths = [p for p in paths if p in changed_inputs]
         if not changed_paths:
           return
         # When merging in other dex files, there's no easy way to know if
         # classes were removed from them.
         if (_AllSubpathsAreClassFiles(changed_paths, changes)
             and not _DexWasEmpty(changed_paths, changes)):
           dex_cmd.append('--incremental')
           for path in changed_paths:
@@ skipping 68 matching lines @@
       options,
       input_paths=input_paths,
       input_strings=dex_cmd,
       output_paths=output_paths,
       force=force,
       pass_changes=True)
 
 
 if __name__ == '__main__':
   sys.exit(main(sys.argv[1:]))