Closure compiler: fix incremental builds

third_party/closure_compiler/compile.py

Index: third_party/closure_compiler/compile.py
diff --git a/third_party/closure_compiler/compile.py b/third_party/closure_compiler/compile.py
index 99d0d103d4d8ba7a3f2d5a9609a5b5629e61f8d0..9132b7d7801d51714aa408e0feea144f2be938e3 100755
--- a/third_party/closure_compiler/compile.py
+++ b/third_party/closure_compiler/compile.py
@@ -183,7 +183,7 @@ class Checker(object):
       tmp_file.write(contents)
     return tmp_file.name
 
-  def _run_js_check(self, sources, out_file=None, externs=None,
+  def _run_js_check(self, sources, out_file, externs=None,
                     closure_args=None):
     """Check |sources| for type errors.
 
@@ -199,10 +199,15 @@ class Checker(object):
     """
     args = ["--js=%s" % s for s in sources]
 
-    if out_file:
-      out_dir = os.path.dirname(out_file)
-      if not os.path.exists(out_dir):
-        os.makedirs(out_dir)
+    assert out_file
+
+    out_dir = os.path.dirname(out_file)
+    if not os.path.exists(out_dir):
+      os.makedirs(out_dir)
+
+    checks_only = 'checks_only' in closure_args
+
+    if not checks_only:
       args += ["--js_output_file=%s" % out_file]
       args += ["--create_source_map=%s" % (self._MAP_FILE_FORMAT % out_file)]
 
@@ -227,11 +232,17 @@ class Checker(object):
       self._nuke_temp_files()
       sys.exit(1)
 
-    if errors and out_file:
+    if errors:
       if os.path.exists(out_file):
         os.remove(out_file)
       if os.path.exists(self._MAP_FILE_FORMAT % out_file):
         os.remove(self._MAP_FILE_FORMAT % out_file)
+    elif checks_only:
+      # Compile succeeded but --checks_only disables --js_output_file from
+      # actually writing a file. Write a file ourselves so incremental builds
+      # still work.
+      with open(out_file, 'w') as f:
+        f.write('')
 
     return errors, stderr
 
@@ -323,7 +334,7 @@ if __name__ == "__main__":
                                  help="Process all source files as a group")
   parser.add_argument("-d", "--depends", nargs=argparse.ZERO_OR_MORE)
   parser.add_argument("-e", "--externs", nargs=argparse.ZERO_OR_MORE)
-  parser.add_argument("-o", "--out_file",
+  parser.add_argument("-o", "--out_file", required=True,
                       help="A file where the compiled output is written to")
   parser.add_argument("-c", "--closure_args", nargs=argparse.ZERO_OR_MORE,
                       help="Arguments passed directly to the Closure compiler")