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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)]