cc/find_cc_toolchain.bzl

# 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.
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#
#    http://www.apache.org/licenses/LICENSE-2.0
#
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# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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"""
Returns the current `CcToolchainInfo`.

* 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("@bazel_tools//tools/cpp:current_cc_toolchain")),
    },
)
* 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:

    foo = rule(
        implementation = _foo_impl,
        toolchains = ["@rules_cc//cc:toolchain_type"],
    )

We advise to depend on both `_cc_toolchain` attr and
`@rules_cc//cc: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
`@rules_cc//cc:toolchain_type`.
"""

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 "//cc:toolchain_type" in ctx.toolchains:
            return ctx.toolchains["//cc:toolchain_type"]
        fail("In order to use find_cc_toolchain, you must include the '@rules_cc//cc:toolchain_type' in the toolchains argument to your rule.")

    # 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_ccc_toolchain, you must define the '_cc_toolchain' attribute on your rule or aspect.")