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# pylint: disable=g-bad-file-header
# Copyright 2016 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.
"""
Helpers for CC Toolchains.
Rules that require a CC toolchain should call `use_cc_toolchain` and `find_cc_toolchain`
to depend on and find a cc toolchain.
* When https://github.com/bazelbuild/bazel/issues/7260 is **not** flipped, current
C++ toolchain is selected using the legacy mechanism (`--crosstool_top`,
`--cpu`, `--compiler`). For that to work the rule needs to declare an
`_cc_toolchain` attribute, e.g.
foo = rule(
implementation = _foo_impl,
attrs = {
"_cc_toolchain": attr.label(
default = Label(
"@rules_cc//cc:current_cc_toolchain", # copybara-use-repo-external-label
),
),
},
)
* When https://github.com/bazelbuild/bazel/issues/7260 **is** flipped, current
C++ toolchain is selected using the toolchain resolution mechanism
(`--platforms`). For that to work the rule needs to declare a dependency on
C++ toolchain type:
load(":find_cc_toolchain/bzl", "use_cc_toolchain")
foo = rule(
implementation = _foo_impl,
toolchains = use_cc_toolchain(),
)
We advise to depend on both `_cc_toolchain` attr and on the toolchain type for
the duration of the migration. After
https://github.com/bazelbuild/bazel/issues/7260 is flipped (and support for old
Bazel version is not needed), it's enough to only keep the toolchain type.
"""
CC_TOOLCHAIN_TYPE = "@bazel_tools//tools/cpp:toolchain_type" # copybara-use-repo-external-label
def find_cc_toolchain(ctx):
"""
Returns the current `CcToolchainInfo`.
Args:
ctx: The rule context for which to find a toolchain.
Returns:
A CcToolchainInfo.
"""
# Check the incompatible flag for toolchain resolution.
if hasattr(cc_common, "is_cc_toolchain_resolution_enabled_do_not_use") and cc_common.is_cc_toolchain_resolution_enabled_do_not_use(ctx = ctx):
if not CC_TOOLCHAIN_TYPE in ctx.toolchains:
fail("In order to use find_cc_toolchain, your rule has to depend on C++ toolchain. See find_cc_toolchain.bzl docs for details.")
toolchain_info = ctx.toolchains[CC_TOOLCHAIN_TYPE]
if toolchain_info == None:
# No cpp toolchain was found, so report an error.
fail("Unable to find a CC toolchain using toolchain resolution. Target: %s, Platform: %s, Exec platform: %s" %
(ctx.label, ctx.fragments.platform.platform, ctx.fragments.platform.host_platform))
if hasattr(toolchain_info, "cc_provider_in_toolchain") and hasattr(toolchain_info, "cc"):
return toolchain_info.cc
return toolchain_info
# Fall back to the legacy implicit attribute lookup.
if hasattr(ctx.attr, "_cc_toolchain"):
return ctx.attr._cc_toolchain[cc_common.CcToolchainInfo]
# We didn't find anything.
fail("In order to use find_cc_toolchain, your rule has to depend on C++ toolchain. See find_cc_toolchain.bzl docs for details.")
def find_cpp_toolchain(ctx):
"""Deprecated, use `find_cc_toolchain` instead.
Args:
ctx: See `find_cc_toolchain`.
Returns:
A CcToolchainInfo.
"""
return find_cc_toolchain(ctx)
def use_cc_toolchain(mandatory = False):
"""
Helper to depend on the cc toolchain.
Usage:
```
my_rule = rule(
toolchains = [other toolchain types] + use_cc_toolchain(),
)
```
Args:
mandatory: Whether or not it should be an error if the toolchain cannot be resolved.
Returns:
A list that can be used as the value for `rule.toolchains`.
"""
return [config_common.toolchain_type(CC_TOOLCHAIN_TYPE, mandatory = mandatory)]
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