rules/filegroup.bzl

"""
Copyright (C) 2021 The Android Open Source Project

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.
"""

load(":cc_constants.bzl", "constants")

def extension(f):
    return f.split(".")[-1]

def group_files_by_ext(files):
    cpp = []
    c = []
    asm = []

    # This for-loop iterator works because filegroups in Android don't use
    # configurable selects.
    for f in files:
        if extension(f) in constants.c_src_exts:
            c += [f]
        elif extension(f) in constants.cpp_src_exts:
            cpp += [f]
        elif extension(f) in constants.as_src_exts:
            asm += [f]
        else:
            # not C based
            continue
    return cpp, c, asm

# Filegroup is a macro because it needs to expand to language specific source
# files for cc_library's srcs_as, srcs_c and srcs attributes.
def filegroup(name, srcs = [], **kwargs):
    native.filegroup(
        name = name,
        srcs = srcs,
        **kwargs
    )

    # These genrule prevent empty filegroups being used as deps to cc libraries,
    # avoiding the error:
    #
    # in srcs attribute of cc_library rule //foo/bar:baz:
    # '//foo/bar/some_other:baz2' does not produce any cc_library srcs files.
    native.genrule(
        name = name + "_null_cc",
        outs = [name + "_null.cc"],
        cmd = "touch $@",
    )
    native.genrule(
        name = name + "_null_c",
        outs = [name + "_null.c"],
        cmd = "touch $@",
    )
    native.genrule(
        name = name + "_null_s",
        outs = [name + "_null.S"],
        cmd = "touch $@",
    )

    cpp_srcs, c_srcs, as_srcs = group_files_by_ext(srcs)
    native.filegroup(
        name = name + "_cpp_srcs",
        srcs = [name + "_null.cc"] + cpp_srcs,
    )
    native.filegroup(
        name = name + "_c_srcs",
        srcs = [name + "_null.c"] + c_srcs,
    )
    native.filegroup(
        name = name + "_as_srcs",
        srcs = [name + "_null.S"] + as_srcs,
    )