gn build: Copy file permissions from input file in configure_file() emulation.

[pcc]

Summary

Most significantly, this makes bin/llvm-lit executable so that it
can be run in the usual way.

[phosek]

llvm/utils/gn/build/write_cmake_config.py

105 ↗

(On Diff #180599)

Shouldn't this be inside the if block so the permissions are only changed if file is actually written?

[pcc]

llvm/utils/gn/build/write_cmake_config.py

105 ↗

(On Diff #180599)

I thought about doing it that way, but figured that we'd want to copy the permissions if the contents don't change but the permissions do. Admittedly this is a bit of an edge case and now that I think about it more I don't even think that ninja will rerun the command in that case. So it would probably be slightly better to move it inside so that we don't disturb the ctime if the file didn't change. I'll do that.

[pcc]

• Move chmod inside the if

[phosek]

LGTM

llvm/trunk/utils/gn/build/write_cmake_config.py

def main():
 
     leftovers = var_re.findall(output)
     if leftovers:
         print('unprocessed values:\n', '\n'.join(leftovers), file=sys.stderr)
         return 1
 
     if not os.path.exists(args.output) or open(args.output).read() != output:
         open(args.output, 'w').write(output)
+        os.chmod(args.output, os.stat(args.input).st_mode & 0777)
 
 
 if __name__ == '__main__':
     sys.exit(main())