Bug 940708 - Part 4: Limit the length of the unified file name prefix to 50 characters so that we don't blow up the Windows path name limit; r=glandium

--HG--
extra : rebase_source : 7f28ada75a26132af951893137127e0f1517995b

python/mozbuild/mozbuild/backend/recursivemake.py

@@ -373,11 +373,18 @@ class RecursiveMakeBackend(CommonBackend):
             for k, v in sorted(obj.variables.items()):
                 if k in unified_suffixes:
                     if do_unify:
+                        # On Windows, path names have a maximum length of 255 characters,
+                        # so avoid creating extremely long path names.
+                        unified_prefix = backend_file.relobjdir
+                        if len(unified_prefix) > 39:
+                            unified_prefix = unified_prefix[-39:].split('/', 1)[-1]
+                        unified_prefix = unified_prefix.replace('/', '_')
+
                         self._add_unified_build_rules(backend_file, v,
                             backend_file.objdir,
                             unified_prefix='Unified_%s_%s' % (
                                 unified_suffixes[k],
-                                backend_file.relobjdir.replace('/', '_')),
+                                unified_prefix),
                             unified_suffix=unified_suffixes[k],
                             unified_files_makefile_variable=k,
                             include_curdir_build_rules=False,