Bug 1491967 - Translate arguments to |./mach build| to objdir paths when possible in the tup backend. r=firefox-build-system-reviewers,mshal

Differential Revision: https://phabricator.services.mozilla.com/D6084

--HG--
extra : moz-landing-system : lando

python/mozbuild/mozbuild/backend/tup.py

@@ -301,6 +301,19 @@ class TupBackend(CommonBackend):
     def build(self, config, output, jobs, verbose, what=None):
         if not what:
             what = ['%s/<default>' % config.topobjdir]
+        else:
+            # Translate relsrcdir paths to the objdir when possible.
+            translated = []
+            topsrcdir = mozpath.normpath(config.topsrcdir)
+            for path in what:
+                path = mozpath.abspath(path)
+                if path.startswith(topsrcdir):
+                    objdir_path = path.replace(topsrcdir, config.topobjdir)
+                    if os.path.exists(objdir_path):
+                        path = objdir_path
+                translated.append(path)
+            what = translated
+
         args = [self.environment.substs['TUP'], 'upd'] + what
         if self.environment.substs.get('MOZ_AUTOMATION'):
             args += ['--quiet']