Resolving full target name in custom build rule

[ker...@google.com]

Within a custom build rule, how can you resolve a relative target name such as :foo to a full target name such as //bar/baz:foo?

For example, if //bar/baz/BUILD contains

py_library(name='foo')

my_custom_rule(arg=':foo')

how can my_custom_rule convert ':foo' into '//bar/baz:foo'?

- Kerrick

[Nathan Harmata]

See PACKAGE_NAME in http://bazel.io/docs/build-encyclopedia.html#predefined-python-variables

--

[Kerrick Staley]

So some code like the following?

def ResolveLabel(label):

  package = label.split(':')[0]

  if not package.startswith('//'):

    package = PACKAGE_NAME + '/' + package

  if ':' in label:

    target = label.split(':')[-1]

  else:

    target = label.split('/')[-1]

  return package + ':' + target

- Kerrick

[Nathan Harmata]

Sure, some string manipulation like that is the right approach.

Though may I ask what you are trying to accomplish? I can't think of a good reason off the top of my head why you would need to do something like this.

[Laurent Le Brun]

If you are using a Skylark macro, see absolute_label.bzl:

load("/tools/build_defs/absolute_label", "absolute_label")

If you have a build extension, see
devtools/buildifier/build_defs/label_with_target
but please note that go/deprecate-preprocessing

> --
>

[Laurent Le Brun]

Sorry, the file isn't shipped yet with Bazel:

def absolute_label(label):
"""Expands a label to be of the full form //package:foo.

absolute_label("//pkg:foo") = "//pkg:foo"
absolute_label("//pkg:gws") = "//pkg:gws"
absolute_label("//pkg") = "//pkg:gws"
absolute_label(":foo") = "//current_package:foo"
"""
if label.startswith("//") and not (":" in label):
label += ":" + label[label.rfind("/")+1:]
elif label.startswith(":"):
label = "//" + PACKAGE_NAME + label
return label

--
Laurent

[Kerrick Staley]

I ended up with this implementation:

def _AbsoluteLabel(label):

  if ':' in label:

    package, target = label.split(':')

  elif '/' in label:

    package = label

    target = label.split('/')[-1]

  else:

    package = ''

    target = label

  if not package.startswith('//'):

    package = '//' + PACKAGE_NAME + ('/' + package if package else '')

  return package + ':' + target

The absolute_label function in that file doesn't seem to handle labels without slashes or a colon, e.g. "foo.py" (and looking at its tests, this seems intentional). I think these should resolve to e.g. //PACKAGE_NAME:foo.py.

- Kerrick