Skylark style guide

[davidzchen]

While Skylark is a Python subset, there are slight differences between Skylark/BUILD style vs. the Google Python conventions. For example (from the Skylark cookbook:

def macro(name, visibility=None):
  # Creating a native genrule.
  native.genrule(
      name = name,
      outs = [name + '.txt'],
      cmd = 'echo hello > $@',
      visibility = visibility,
  )

Rule invocations such as native.genrule() follow the BUILD style rather than the standard Python function call style.

I think it would be good to write a Skylark Style Guide that defines a convention for Skylark code and lists some best practices.

[kjiwa]

A tool like Chromium's gn format or Closure's fixjsstyle that can automatically clean up BUILD and *.bzl files would be nice along with this. e.g. find -name BUILD -exec gn format {} \;.

See https://code.google.com/p/chromium/codesearch#chromium/src/tools/gn/command_format.cc as an example of a tool that uses a BUILD-like syntax.

[jbduncan]

I'm not sure that this is an issue anymore, given that a BUILD file formatter apparently exists.

[softprops]

Are there any differences between build file formatting and .bzl files?

[jbduncan]

Good question. I'm new to Bazel, so I didn't realise that there was a difference between the two.

From my current understanding, both BUILD and .bzl files follow the Skylark syntax, so I'd be a little surprised if the BUILD file formatter couldn't format .bzl files as well.

[jbduncan]

Ah, I'm probably mistaken, as there seem to be different style guides for BUILD and .bzl files, which implies to me that there's a difference that is not too obvious.

[laurentlb]

Style guide and formatter are different things.

You don't put the same things in BUILD files and in bzl files, so it's better to have separate style guides.
Buildifier cannot format .bzl files yet (it will skip function definitions).

[laurentlb]

Closing this issue. We have now much more information in the documentation (see Best practices) and a code formatter.

https://docs.bazel.build/versions/master/skylark/bzl-style.html
https://github.com/bazelbuild/buildtools