Add an open-source version of find_cpp_toolchain, to allow open-source users of
the CppConfiguration Skylark API to migrate to platforms and toolchains.
For more details on toolchains, please see https://docs.google.com/document/d/1-G-VPRLEj9VyfC6VrQBiR8To-dZjnBSQS66Y4nargGM/edit#heading=h.al54v2ddwqzv
PiperOrigin-RevId: 177811908
diff --git a/tools/cpp/toolchain_utils.bzl b/tools/cpp/toolchain_utils.bzl
new file mode 100644
index 0000000..83d0707
--- /dev/null
+++ b/tools/cpp/toolchain_utils.bzl
@@ -0,0 +1,54 @@
+# 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.
+
+"""Finds the c++ toolchain if it is enabled.
+
+Otherwise, falls back to a toolchain constructed from the CppConfiguration.
+"""
+
+def _get_cpp_toolchain_attr(ctx, attr):
+ if hasattr(ctx.attr._cc_toolchain[cc_common.CcToolchainInfo], attr):
+ return getattr(ctx.attr._cc_toolchain[cc_common.CcToolchainInfo], attr)
+ else:
+ return getattr(ctx.fragments.cpp, attr)
+
+def _make_legacy_toolchain(ctx):
+ return struct(
+ objcopy_executable = _get_cpp_toolchain_attr(ctx, "objcopy_executable"),
+ compiler_executable = _get_cpp_toolchain_attr(ctx, "compiler_executable"),
+ preprocessor_executable = _get_cpp_toolchain_attr(ctx, "preprocessor_executable"),
+ nm_executable = _get_cpp_toolchain_attr(ctx, "nm_executable"),
+ objdump_executable = _get_cpp_toolchain_attr(ctx, "objdump_executable"),
+ ar_executable = _get_cpp_toolchain_attr(ctx, "ar_executable"),
+ strip_executable = _get_cpp_toolchain_attr(ctx, "strip_executable"),
+ ld_executable = _get_cpp_toolchain_attr(ctx, "ld_executable"),
+ )
+
+def find_cpp_toolchain(ctx):
+ """If the c++ toolchain is in use, returns it.
+
+ Otherwise, returns a c++ toolchain derived from legacy toolchain selection.
+
+ Args:
+ ctx: The rule context for which to find a toolchain.
+
+ Returns:
+ A CcToolchainProvider.
+ """
+
+ if Label("@bazel_tools//tools/cpp:toolchain_type") in ctx.fragments.platform.enabled_toolchain_types:
+ return ctx.toolchains["@bazel_tools//tools/cpp:toolchain_type"]
+ else:
+ return _make_legacy_toolchain(ctx)
