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Diffstat (limited to 'cc/find_cc_toolchain.bzl')
-rw-r--r-- | cc/find_cc_toolchain.bzl | 117 |
1 files changed, 117 insertions, 0 deletions
diff --git a/cc/find_cc_toolchain.bzl b/cc/find_cc_toolchain.bzl new file mode 100644 index 0000000..d2f2d9f --- /dev/null +++ b/cc/find_cc_toolchain.bzl @@ -0,0 +1,117 @@ +# 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)] |