rules/gensrcs.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("@bazel_skylib//lib:paths.bzl", "paths")

# A rule to generate files based on provided srcs and tools
def _gensrcs_impl(ctx):
    # The next two assignments can be created by using ctx.resolve_command
    # TODO: Switch to using ctx.resolve_command when it is out of experimental
    command = ctx.expand_location(ctx.attr.cmd, targets = ctx.attr.data)
    tools = [
        tool[DefaultInfo].files_to_run
        for tool in ctx.attr.tools
    ]

    command = command.replace(
        "$(RULEDIR)",
        paths.join(
            ctx.var["GENDIR"],
            ctx.label.package,
        ),
    )

    in_files = ctx.files.srcs
    out_files = []
    for in_file in in_files:
        # <path-to-in_file>/out_file
        # where path-to-in_file is relative to the workspace
        out_file_path = paths.join(
            paths.dirname(in_file.short_path),
            paths.replace_extension(
                in_file.basename,
                "." + ctx.attr.output_extension,
            ),
        )

        # out_file is at output_file_path that is relative to <GENDIR>/<package-dir>
        # Hence, the fullpath to out_file is
        # <GENDIR>/<package-dir>/<path-to-in_file>/out_file
        out_file = ctx.actions.declare_file(out_file_path)
        shell_command = command \
            .replace("$(SRC)", in_file.path) \
            .replace("$(OUT)", out_file.path)
        ctx.actions.run_shell(
            tools = tools,
            outputs = [out_file],
            inputs = in_files + ctx.files.data,
            command = shell_command,
            progress_message = "Generating %s from %s" % (
                out_file.path,
                in_file.path,
            ),
        )
        out_files.append(out_file)

    return [DefaultInfo(
        files = depset(out_files),
    )]

gensrcs = rule(
    implementation = _gensrcs_impl,
    doc = "This rule generates files, where each of the `srcs` files is " +
          "passed into the custom shell command`",
    attrs = {
        "srcs": attr.label_list(
            allow_files = True,
            mandatory = True,
            doc = "A list of inputs such as source files to process",
        ),
        "output_extension": attr.string(
            doc = "The extension that will be substituted for output files",
        ),
        "cmd": attr.string(
            mandatory = True,
            doc = "The command to run. Subject to $(location) expansion. " +
                  "$(IN) represents each input file provided in `srcs` " +
                  "while $(OUT) reprensents corresponding output file " +
                  "generated by the rule. $(RULEDIR) is intepreted the same " +
                  "as it is in genrule.",
        ),
        "tools": attr.label_list(
            allow_files = True,
            doc = "A list of tool dependencies for this rule. " +
                  "The path of an individual `tools` target //x:y can be " +
                  "obtained using `$(location //x:y)`",
            cfg = "exec",
        ),
        "data": attr.label_list(
            allow_files = True,
            doc = "Additional files needed for build that are not tooling " +
                  "related.",
        ),
    },
)