Closure compiler: fix incremental builds

third_party/closure_compiler/compile2.py

 #!/usr/bin/python
 # Copyright 2015 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.
 
 """Runs Closure compiler on JavaScript files to check for errors and produce
 minified output."""
 
 import argparse
 import os
@@ skipping 170 matching lines @@
       content: A string of the file contens to write to a temporary file.
 
     Return:
       The filepath of the newly created, written, and closed temporary file.
     """
     with tempfile.NamedTemporaryFile(mode="wt", delete=False) as tmp_file:
       self._temp_files.append(tmp_file.name)
       tmp_file.write(contents)
     return tmp_file.name
 
-  def check(self, sources, out_file=None, closure_args=None,
+  def check(self, sources, out_file, closure_args=None,
             custom_sources=True):
     """Closure compile |sources| while checking for errors.
 
     Args:
       sources: Files to check. sources[0] is the typically the target file.
           sources[1:] are externs and dependencies in topological order. Order
           is not guaranteed if custom_sources is True.
       out_file: A file where the compiled output is written to.
       closure_args: Arguments passed directly to the Closure compiler.
       custom_sources: Whether |sources| was customized by the target (e.g. not
@@ skipping 41 matching lines @@
 
       js_args = [self._expanded_file]
 
     closure_args = closure_args or []
     closure_args += ["summary_detail_level=3", "continue_after_errors"]
 
     args = ["--externs=%s" % e for e in externs] + \
            ["--js=%s" % s for s in js_args] + \
            ["--%s" % arg for arg in closure_args]
 
-    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)]
 
     self._log_debug("Args: %s" % " ".join(args))
 
     _, stderr = self._run_jar(self._compiler_jar, args)
 
     errors = stderr.strip().split("\n\n")
     maybe_summary = errors.pop()
 
     summary = re.search("(?P<error_count>\d+).*error.*warning", maybe_summary)
     if summary:
       self._log_debug("Summary: %s" % maybe_summary)
     else:
       # Not a summary. Running the jar failed. Bail.
       self._log_error(stderr)
       self._nuke_temp_files()
       sys.exit(1)
 
-    if summary.group('error_count') != "0" and out_file:
+    if summary.group('error_count') != "0":
       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('')
 
     if not custom_sources:
       filtered_errors = self._filter_errors(errors)
       errors = map(self._clean_up_error, filtered_errors)
       output = self._format_errors(errors)
 
       if errors:
         prefix = "\n" if output else ""
         self._log_error("Error in: %s%s%s" % (self._target, prefix, output))
       elif output:
         self._log_debug("Output: %s" % output)
 
     self._nuke_temp_files()
     return bool(errors), stderr
 
 
 if __name__ == "__main__":
   parser = argparse.ArgumentParser(
       description="Typecheck JavaScript using Closure compiler")
   parser.add_argument("sources", nargs=argparse.ONE_OR_MORE,
                       help="Path to a source file to typecheck")
   parser.add_argument("--custom_sources", action="store_true",
                       help="Whether this rules has custom sources.")
-  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")
   parser.add_argument("-v", "--verbose", action="store_true",
                       help="Show more information as this script runs")
   opts = parser.parse_args()
 
   checker = Checker(verbose=opts.verbose)
 
   found_errors, stderr = checker.check(opts.sources, out_file=opts.out_file,
                                        closure_args=opts.closure_args,
                                        custom_sources=opts.custom_sources)
 
   if found_errors:
     if opts.custom_sources:
       print stderr
     sys.exit(1)