Re: [PATCH v2 1/5] libxl: Generate golang bindings in libxl Makefile

[Ian Jackson <ian.jackson@citrix.com>]

George Dunlap writes ("Re: [PATCH v2 1/5] libxl: Generate golang bindings in libxl Makefile"):
> \x10So as written this turns out not to work correctly:  `gengotypes.py` spits out syntactically valid but unformatted Go code, and then runs `go fmt` on it to get the right style (including tabs, &c).  But the error code of `go fmt` isn’t checked; so on a system without go installed, if the build system decides it needs to re-run `gengotypes.py` for whatever reason, the build succeeds but the tree ends up “dirtied” with an unformatted version fo the generated text.

And `go fmt' overwrites its input file ?

The lost error is due to using `os.system' which does not raise an
exception.  The python 3 docs for `os.system' say
  | The subprocess module provides more powerful facilities for
  | spawning new processes and retrieving their results; using that
  | module is preferable to using this function. See the Replacing
  | Older Functions with the subprocess Module section in the
  | subprocess documentation for some helpful recipes.
And the recipe suggests
  | sts = os.system("mycmd" + " myarg")
  | # becomes
  | sts = call("mycmd" + " myarg", shell=True)
  | Notes:
  | * Calling the program through the shell is usually not required.
    
This is not particularly helpful advice because subprocess.call, like
os.system, does not raise an exception when things go wrong.  But it
does have a "more realistic example" immediately afterwards which does
actually check the error code.

You wanted subprocess.check_call.  IDK which Python versions have
subprocess.check_call.

Ian.