skylark_library.bzl

# Copyright 2017 The Bazel Authors. All rights reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#    http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

"""Skylib module containing a library rule for aggregating rules files."""

SkylarkLibraryInfo = provider(
    'Information on contained Skylark rules.',
    fields={
      'srcs': 'Top level rules files.',
      'transitive_srcs': 'Transitive closure of rules files required for ' +
          'interpretation of the srcs',
    },
)

def _skylark_library_impl(ctx):
  all_files = depset(ctx.files.srcs, order="postorder")
  for dep in ctx.attr.deps:
    all_files += dep.files
  return [
      # All dependent files should be listed in both `files` and in `runfiles`;
      # this ensures that a `skylark_library` can be referenced as `data` from
      # a separate program, or from `tools` of a genrule().
      DefaultInfo(
          files=all_files,
          runfiles=ctx.runfiles(files=list(all_files)),
      ),

      # We also define our own provider struct, for aggregation and testing.
      SkylarkLibraryInfo(
          srcs=ctx.files.srcs,
          transitive_srcs=all_files,
      ),
  ]

skylark_library = rule(
    implementation=_skylark_library_impl,
    attrs={
        "srcs": attr.label_list(
            allow_files=[".bzl"],
        ),
        "deps": attr.label_list(
            allow_files=[".bzl"],
            providers=[
                [SkylarkLibraryInfo],
            ],
        )
    }
)
"""Creates a logical collection of Skylark .bzl files.

Args:
  srcs: List of `.bzl` files that are processed to create this target.
  deps: List of other `skylark_library` targets that are required by the
    Skylark files listed in `srcs`.

Example:
  Suppose your project has the following structure:

  ```
  [workspace]/
      WORKSPACE
      BUILD
      checkstyle/
          BUILD
          checkstyle.bzl
      lua/
          BUILD
          lua.bzl
          luarocks.bzl
  ```

  In this case, you can have `skylark_library` targets in `checkstyle/BUILD` and
  `lua/BUILD`:

  `checkstyle/BUILD`:

  ```python
  load("@bazel_skylib//:skylark_library.bzl", "skylark_library")

  skylark_library(
      name = "checkstyle-rules",
      srcs = ["checkstyle.bzl"],
  )
  ```

  `lua/BUILD`:

  ```python
  load("@bazel_skylib//:skylark_library.bzl", "skylark_library")

  skylark_library(
      name = "lua-rules",
      srcs = [
          "lua.bzl",
          "luarocks.bzl",
      ],
  )
  ```
"""