python/private/stamp_impl.bzl

# Copyright 2023 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,
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"""A small utility module dedicated to detecting whether or not the `--stamp` flag is enabled

This module can be removed likely after the following PRs ar addressed:
- https://github.com/bazelbuild/bazel/issues/11164
"""

load(":visibility.bzl", "NOT_ACTUALLY_PUBLIC")

StampSettingInfo = provider(
    doc = "Information about the `--stamp` command line flag",
    fields = {
        "value": "bool: Whether or not the `--stamp` flag was enabled",
    },
)

def _stamp_build_setting_impl(ctx):
    return StampSettingInfo(value = ctx.attr.value)

_stamp_build_setting = rule(
    doc = """\
Whether to encode build information into the binary. Possible values:

- stamp = 1: Always stamp the build information into the binary, even in [--nostamp][stamp] builds. \
This setting should be avoided, since it potentially kills remote caching for the binary and \
any downstream actions that depend on it.
- stamp = 0: Always replace build information by constant values. This gives good build result caching.
- stamp = -1: Embedding of build information is controlled by the [--[no]stamp][stamp] flag.

Stamped binaries are not rebuilt unless their dependencies change.
[stamp]: https://docs.bazel.build/versions/main/user-manual.html#flag--stamp
    """,
    implementation = _stamp_build_setting_impl,
    attrs = {
        "value": attr.bool(
            doc = "The default value of the stamp build flag",
            mandatory = True,
        ),
    },
)

def stamp_build_setting(name, visibility = NOT_ACTUALLY_PUBLIC):
    native.config_setting(
        name = "stamp_detect",
        values = {"stamp": "1"},
        visibility = visibility,
    )

    _stamp_build_setting(
        name = name,
        value = select({
            ":stamp_detect": True,
            "//conditions:default": False,
        }),
        visibility = visibility,
    )

def is_stamping_enabled(attr):
    """Determine whether or not build stamping is enabled

    Args:
        attr (struct): A rule's struct of attributes (`ctx.attr`)

    Returns:
        bool: The stamp value
    """
    stamp_num = getattr(attr, "stamp", -1)
    if stamp_num == 1:
        return True
    elif stamp_num == 0:
        return False
    elif stamp_num == -1:
        stamp_flag = getattr(attr, "_stamp_flag", None)
        return stamp_flag[StampSettingInfo].value if stamp_flag else False
    else:
        fail("Unexpected `stamp` value: {}".format(stamp_num))