Add a PRESUBMIT for gn check, currently only for //sky/*

PRESUBMIT.py

Index: PRESUBMIT.py
diff --git a/PRESUBMIT.py b/PRESUBMIT.py
index 1f2067ddbfa81096f87d4d886788b05ed19617de..f54a03b178732846386c612fcc06dbbbf8a41cbd 100644
--- a/PRESUBMIT.py
+++ b/PRESUBMIT.py
@@ -412,6 +412,29 @@ def _CheckValidHostsInDEPS(input_api, output_api):
         long_text=error.output)]
 
 
+def _CheckGNCheck(input_api, output_api):
+  """Checks that gn gen and gn check pass"""
+  # TODO(eseidel): We should not have to pass dir= here but unfortunately

[jamesr, 2014/10/31 19:57:45]

could this be a bug? or do we have a bug?

+  # build/config/clang/BUILD.gn:19 rebase_path can't handle absolute paths!
+  temp_dir = input_api.change.RepositoryRoot()
+  out_dir = input_api.tempfile.mkdtemp(dir=temp_dir)
+  relative_out_dir = input_api.os_path.relpath(out_dir)
+  try:
+    input_api.subprocess.check_output(['gn', 'gen', relative_out_dir])
+  except input_api.subprocess.CalledProcessError, error:
+    return [output_api.PresubmitError(
+        'gn gen must not fail.', long_text=error.output)]
+
+  try:
+    # TODO(eseidel): Currently only //sky/* are known to pass.
+    input_api.subprocess.check_output(['gn', 'check', relative_out_dir,
+        '//sky/*'])

[jamesr, 2014/10/31 19:57:45]

can we make this a list somewhere? i made //mojo/public/* pass a while ago and
i'd like to add that

+  except input_api.subprocess.CalledProcessError, error:
+    return [output_api.PresubmitError(
+        'gn check must not fail.', long_text=error.output)]
+  return []
+
+
 def _CheckNoBannedFunctions(input_api, output_api):
   """Make sure that banned functions are not used."""
   warnings = []
@@ -1292,6 +1315,7 @@ def _CommonChecks(input_api, output_api):
   results.extend(_CheckParseErrors(input_api, output_api))
   results.extend(_CheckForIPCRules(input_api, output_api))
   results.extend(_CheckForOverrideAndFinalRules(input_api, output_api))
+  results.extend(_CheckGNCheck(input_api, output_api))
 
   if any('PRESUBMIT.py' == f.LocalPath() for f in input_api.AffectedFiles()):
     results.extend(input_api.canned_checks.RunUnitTestsInDirectory(