GN: Avoid nontrivial shell commands in gcc_toolchain tools

build/toolchain/gcc_ar_wrapper.py

+#!/usr/bin/env 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 the 'ar' command after removing its output file first.
+
+This script is invoked like:
+  python gcc_ar_wrapper.py --ar=$AR --output=$OUT $OP $INPUTS
+to do the equivalent of:
+  rm -f $OUT && $AR $OP $OUT $INPUTS
+"""
+
+import argparse
+import os
+import subprocess
+import sys
+
+
+def main():
+  parser = argparse.ArgumentParser(description=__doc__)
+  parser.add_argument('--ar',
+                      required=True,
+                      help='The ar binary to run',
+                      metavar='PATH')
+  parser.add_argument('--output',
+                      required=True,
+                      help='Output archive file',
+                      metavar='ARCHIVE')
+  parser.add_argument('operation',
+                      help='Operation on the archive')
+  parser.add_argument('--plugin',
+                      help='Load plugin')

[Dirk Pranke, 2015/10/28 22:13:03]

nit: I'd reorder --plugin before operation.

[Roland McGrath, 2015/10/28 22:25:16]

Done.  I originally wrote them in the order they are actually used on the
command line.

+  parser.add_argument('inputs', nargs='+',
+                      help='Input files')
+  args = parser.parse_args()
+
+  command = [args.ar, args.operation]
+  if args.plugin is not None:
+    command += ['--plugin', args.plugin]
+  command.append(args.output)
+  command += args.inputs
+
+  # Remove the output file first.
+  try:
+    os.remove(args.output)
+  except OSError:
+    pass

[Dirk Pranke, 2015/10/28 22:13:03]

I suspect you shouldn't be ignoring the error here ...

[Roland McGrath, 2015/10/28 22:25:15]

Ignoring the error is the equivalent of 'rm -f', which is what this is
replacing.
It could do if os.path.exists: os.remove, but that is costlier and racy.

+
+  # Now just run the ar command.
+  return subprocess.call(command)
+
+
+if __name__ == "__main__":
+  sys.exit(main())