Add cc_legacy_tool stopgap

Some tools in rules_cc like gcov and llvm-cov, expect absolute paths in
the toolchain. This clearly isn't ideal but updating all callers as a
blocker to being able to use rules based toolchains also isn't ideal.
This allows backfilling those absolute tool paths with the new
cc_legacy_tool rule.

Author: keith

cc/toolchains/cc_toolchain_info.bzl

@@ -221,6 +221,16 @@ ToolConfigInfo = provider(
     },
 )
 
+LegacyToolInfo = provider(
+    doc = "A tool specified by path rather than by label, for legacy toolchain configurations.",
+    # @unsorted-dict-items
+    fields = {
+        "label": "(Label) The label defining this provider. Place in error messages to simplify debugging",
+        "name": "(str) The tool name (eg. gcc, ar, ld, strip)",
+        "path": "(str) The filesystem path to the tool",
+    },
+)
+
 ToolchainConfigInfo = provider(
     doc = "The configuration for a toolchain",
     # @unsorted-dict-items
@@ -235,5 +245,6 @@ ToolchainConfigInfo = provider(
         "files": "(dict[ActionTypeInfo, depset[File]]) Files required for the toolchain, keyed by the action type.",
         "allowlist_include_directories": "(depset[DirectoryInfo]) Built-in include directories implied by this toolchain's args and tools that should be allowlisted in Bazel's include checker",
         "allowlist_absolute_include_directories": "(List[str]) Built-in include directories allowed the sandbox. Use with care",
+        "legacy_tools": "(Sequence[LegacyToolInfo]) Legacy tools specified by path rather than by label",
     },
 )

cc/toolchains/impl/legacy_converter.bzl

@@ -24,6 +24,7 @@ load(
     legacy_flag_set = "flag_set",
     legacy_make_variable = "make_variable",
     legacy_tool = "tool",
+    legacy_tool_path = "tool_path",
     legacy_with_feature_set = "with_feature_set",
 )
 
@@ -226,10 +227,19 @@ def convert_toolchain(toolchain):
         for m in toolchain.make_variables
     ]
 
+    tool_paths = [
+        legacy_tool_path(
+            name = lt.name,
+            path = lt.path,
+        )
+        for lt in toolchain.legacy_tools
+    ]
+
     return struct(
         features = [ft for ft in features if ft != None],
         action_configs = sorted(action_configs, key = lambda ac: ac.action_name),
         cxx_builtin_include_directories = cxx_builtin_include_directories,
         artifact_name_patterns = artifact_name_patterns,
         make_variables = make_variables,
+        tool_paths = tool_paths,
     )

cc/toolchains/impl/toolchain_config.bzl

@@ -20,6 +20,7 @@ load(
     "ArgsListInfo",
     "ArtifactNamePatternInfo",
     "FeatureSetInfo",
+    "LegacyToolInfo",
     "MakeVariableInfo",
     "ToolConfigInfo",
     "ToolchainConfigInfo",
@@ -62,6 +63,7 @@ def _cc_toolchain_config_impl(ctx):
         args = ctx.attr.args,
         artifact_name_patterns = ctx.attr.artifact_name_patterns,
         make_variables = ctx.attr.make_variables,
+        legacy_tools = ctx.attr.legacy_tools,
     )
 
     legacy = convert_toolchain(toolchain_config)
@@ -75,6 +77,7 @@ def _cc_toolchain_config_impl(ctx):
             make_variables = legacy.make_variables,
             features = legacy.features,
             cxx_builtin_include_directories = legacy.cxx_builtin_include_directories,
+            tool_paths = legacy.tool_paths,
             # toolchain_identifier is deprecated, but setting it to None results
             # in an error that it expected a string, and for safety's sake, I'd
             # prefer to provide something unique.
@@ -111,6 +114,7 @@ cc_toolchain_config = rule(
         "enabled_features": attr.label_list(providers = [FeatureSetInfo]),
         "artifact_name_patterns": attr.label_list(providers = [ArtifactNamePatternInfo]),
         "make_variables": attr.label_list(providers = [MakeVariableInfo]),
+        "legacy_tools": attr.label_list(providers = [LegacyToolInfo]),
         "_builtin_features": attr.label(default = "//cc/toolchains/features:all_builtin_features"),
     },
     provides = [ToolchainConfigInfo],

cc/toolchains/impl/toolchain_config_info.bzl

@@ -13,7 +13,7 @@
 # limitations under the License.
 """Helper functions to create and validate a ToolchainConfigInfo."""
 
-load("//cc/toolchains:cc_toolchain_info.bzl", "ArtifactNamePatternInfo", "MakeVariableInfo", "ToolConfigInfo", "ToolchainConfigInfo")
+load("//cc/toolchains:cc_toolchain_info.bzl", "ArtifactNamePatternInfo", "LegacyToolInfo", "MakeVariableInfo", "ToolConfigInfo", "ToolchainConfigInfo")
 load(":args_utils.bzl", "get_action_type")
 load(":collect.bzl", "collect_args_lists", "collect_features")
 
@@ -162,7 +162,7 @@ def _collect_make_variables(targets, fail):
 
     return make_variables.values()
 
-def toolchain_config_info(label, known_features = [], enabled_features = [], args = [], artifact_name_patterns = [], make_variables = [], tool_map = None, fail = fail):
+def toolchain_config_info(label, known_features = [], enabled_features = [], args = [], artifact_name_patterns = [], make_variables = [], legacy_tools = [], tool_map = None, fail = fail):
     """Generates and validates a ToolchainConfigInfo from lists of labels.
 
     Args:
@@ -173,6 +173,7 @@ def toolchain_config_info(label, known_features = [], enabled_features = [], arg
         args: (List[Target]) A list of targets providing ArgsListInfo
         artifact_name_patterns: (List[Target]) A list of targets providing ArtifactNamePatternInfo.
         make_variables: (List[Target]) A list of targets providing MakeVariableInfo.
+        legacy_tools: (List[Target]) A list of targets providing LegacyToolInfo.
         tool_map: (Target) A target providing ToolMapInfo.
         fail: A fail function. Use only during tests.
     Returns:
@@ -193,6 +194,8 @@ def toolchain_config_info(label, known_features = [], enabled_features = [], arg
         # side-effect of allowing code to continue.
         return None  # buildifier: disable=unreachable
 
+    legacy_tools_infos = tuple([t[LegacyToolInfo] for t in legacy_tools])
+
     args = collect_args_lists(args, label = label)
     tools = tool_map[ToolConfigInfo].configs
     files = {
@@ -222,6 +225,7 @@ def toolchain_config_info(label, known_features = [], enabled_features = [], arg
         allowlist_absolute_include_directories = allowlist_absolute_include_directories,
         artifact_name_patterns = _collect_artifact_name_patterns(artifact_name_patterns, fail),
         make_variables = _collect_make_variables(make_variables, fail),
+        legacy_tools = legacy_tools_infos,
     )
     _validate_toolchain(toolchain_config, fail = fail)
     return toolchain_config

cc/toolchains/legacy_tool.bzl

@@ -0,0 +1,63 @@
+# Copyright 2026 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.
+"""Implementation of cc_legacy_tool"""
+
+load(":cc_toolchain_info.bzl", "LegacyToolInfo")
+
+def _cc_legacy_tool_impl(ctx):
+    return [LegacyToolInfo(
+        label = ctx.label,
+        name = ctx.attr.tool_name,
+        path = ctx.attr.path,
+    )]
+
+cc_legacy_tool = rule(
+    implementation = _cc_legacy_tool_impl,
+    attrs = {
+        "tool_name": attr.string(
+            mandatory = True,
+            doc = """The name of the tool (eg. "gcc", "ar", "ld", "strip").
+
+This corresponds to the tool name used by Bazel's legacy toolchain resolution.
+""",
+        ),
+        "path": attr.string(
+            mandatory = True,
+            doc = """The filesystem path to the tool.
+
+Can be an absolute path (for non-hermetic toolchains) or a relative path
+starting from the package that provides the toolchain.
+""",
+        ),
+    },
+    provides = [LegacyToolInfo],
+    doc = """Declares a tool by filesystem path for use in legacy toolchain configurations.
+
+`cc_legacy_tool` allows specifying tools by their filesystem path rather than as
+Bazel targets. This is useful where bazel doesn't handle relative paths well.
+
+These tools are passed via the `legacy_tools` attribute of `cc_toolchain`.
+
+Example:
+```
+load("@rules_cc//cc/toolchains:legacy_tool.bzl", "cc_legacy_tool")
+
+cc_legacy_tool(
+    name = "gcov",
+    tool_name = "gcov",
+    path = "/usr/bin/gcov",
+)
+```
+""",
+)

cc/toolchains/toolchain.bzl

@@ -61,6 +61,7 @@ def cc_toolchain(
         args = [],
         artifact_name_patterns = [],
         make_variables = [],
+        legacy_tools = [],
         known_features = [],
         enabled_features = [],
         libc_top = None,
@@ -118,6 +119,9 @@ def cc_toolchain(
         artifact_name_patterns: (List[Label]) A list of `cc_artifact_name_pattern` defining patterns
             for names of artifacts created by this toolchain.
         make_variables: (List[Label]) A list of `cc_make_variable` defining variable substitutions.
+        legacy_tools: (List[Label]) A list of `cc_legacy_tool` rules that specify tools by filesystem
+            path. These are used to populate the legacy `tool_paths` parameter of the toolchain
+            configuration, which is required by some Bazel features (e.g. coverage).
         known_features: (List[Label]) A list of `cc_feature` rules that this toolchain supports.
             Whether or not these
             [features](https://bazel.build/docs/cc-toolchain-config-reference#features)
@@ -174,6 +178,7 @@ def cc_toolchain(
         args = args,
         artifact_name_patterns = artifact_name_patterns,
         make_variables = make_variables,
+        legacy_tools = legacy_tools,
         known_features = known_features,
         enabled_features = enabled_features,
         compiler = compiler,

docs/toolchain_api.md

@@ -785,9 +785,9 @@ cc_tool_map(
 <pre>
 load("@rules_cc//cc/toolchains/impl:documented_api.bzl", "cc_toolchain")
 
-cc_toolchain(*, <a href="#cc_toolchain-name">name</a>, <a href="#cc_toolchain-tool_map">tool_map</a>, <a href="#cc_toolchain-args">args</a>, <a href="#cc_toolchain-artifact_name_patterns">artifact_name_patterns</a>, <a href="#cc_toolchain-make_variables">make_variables</a>, <a href="#cc_toolchain-known_features">known_features</a>,
-             <a href="#cc_toolchain-enabled_features">enabled_features</a>, <a href="#cc_toolchain-libc_top">libc_top</a>, <a href="#cc_toolchain-module_map">module_map</a>, <a href="#cc_toolchain-dynamic_runtime_lib">dynamic_runtime_lib</a>, <a href="#cc_toolchain-static_runtime_lib">static_runtime_lib</a>,
-             <a href="#cc_toolchain-supports_header_parsing">supports_header_parsing</a>, <a href="#cc_toolchain-supports_param_files">supports_param_files</a>, <a href="#cc_toolchain-compiler">compiler</a>, <a href="#cc_toolchain-kwargs">**kwargs</a>)
+cc_toolchain(*, <a href="#cc_toolchain-name">name</a>, <a href="#cc_toolchain-tool_map">tool_map</a>, <a href="#cc_toolchain-args">args</a>, <a href="#cc_toolchain-artifact_name_patterns">artifact_name_patterns</a>, <a href="#cc_toolchain-make_variables">make_variables</a>, <a href="#cc_toolchain-legacy_tools">legacy_tools</a>,
+             <a href="#cc_toolchain-known_features">known_features</a>, <a href="#cc_toolchain-enabled_features">enabled_features</a>, <a href="#cc_toolchain-libc_top">libc_top</a>, <a href="#cc_toolchain-module_map">module_map</a>, <a href="#cc_toolchain-dynamic_runtime_lib">dynamic_runtime_lib</a>,
+             <a href="#cc_toolchain-static_runtime_lib">static_runtime_lib</a>, <a href="#cc_toolchain-supports_header_parsing">supports_header_parsing</a>, <a href="#cc_toolchain-supports_param_files">supports_param_files</a>, <a href="#cc_toolchain-compiler">compiler</a>, <a href="#cc_toolchain-kwargs">**kwargs</a>)
 </pre>
 
 A C/C++ toolchain configuration.
@@ -840,6 +840,7 @@ Generated rules:
 | <a id="cc_toolchain-args"></a>args |  (List[Label]) A list of [`cc_args`](#cc_args) and `cc_arg_list` to apply across this toolchain.   |  `[]` |
 | <a id="cc_toolchain-artifact_name_patterns"></a>artifact_name_patterns |  (List[Label]) A list of `cc_artifact_name_pattern` defining patterns for names of artifacts created by this toolchain.   |  `[]` |
 | <a id="cc_toolchain-make_variables"></a>make_variables |  (List[Label]) A list of `cc_make_variable` defining variable substitutions.   |  `[]` |
+| <a id="cc_toolchain-legacy_tools"></a>legacy_tools |  (List[Label]) A list of `cc_legacy_tool` rules that specify tools by filesystem path. These are used to populate the legacy `tool_paths` parameter of the toolchain configuration, which is required by some Bazel features (e.g. coverage).   |  `[]` |
 | <a id="cc_toolchain-known_features"></a>known_features |  (List[Label]) A list of [`cc_feature`](#cc_feature) rules that this toolchain supports. Whether or not these [features](https://bazel.build/docs/cc-toolchain-config-reference#features) are enabled may change over the course of a build. See the documentation for [`cc_feature`](#cc_feature) for more information.   |  `[]` |
 | <a id="cc_toolchain-enabled_features"></a>enabled_features |  (List[Label]) A list of [`cc_feature`](#cc_feature) rules whose initial state should be `enabled`. Note that it is still possible for these [features](https://bazel.build/docs/cc-toolchain-config-reference#features) to be disabled over the course of a build through other mechanisms. See the documentation for [`cc_feature`](#cc_feature) for more information.   |  `[]` |
 | <a id="cc_toolchain-libc_top"></a>libc_top |  (Label) A collection of artifacts for libc passed as inputs to compile/linking actions. See [`cc_toolchain.libc_top`](https://bazel.build/reference/be/c-cpp#cc_toolchain.libc_top) for more information.   |  `None` |

tests/rule_based_toolchain/legacy_tool/BUILD

@@ -0,0 +1,16 @@
+load("//cc/toolchains:legacy_tool.bzl", "cc_legacy_tool")
+load("//tests/rule_based_toolchain:analysis_test_suite.bzl", "analysis_test_suite")
+load(":legacy_tool_test.bzl", "TARGETS", "TESTS")
+
+cc_legacy_tool(
+    name = "gcov_tool",
+    path = "/usr/bin/gcov",
+    tool_name = "gcov",
+    visibility = ["//tests/rule_based_toolchain:__subpackages__"],
+)
+
+analysis_test_suite(
+    name = "test_suite",
+    targets = TARGETS,
+    tests = TESTS,
+)

tests/rule_based_toolchain/legacy_tool/legacy_tool_test.bzl

@@ -0,0 +1,32 @@
+# Copyright 2026 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.
+"""Tests for the cc_legacy_tool rule."""
+
+load("//cc/toolchains:cc_toolchain_info.bzl", "LegacyToolInfo")
+
+visibility("private")
+
+def _legacy_tool_provides_info_test(env, targets):
+    info = targets.gcov_tool[LegacyToolInfo]
+    env.expect.that_str(info.name).equals("gcov")
+    env.expect.that_str(info.path).equals("/usr/bin/gcov")
+
+TARGETS = [
+    ":gcov_tool",
+]
+
+# @unsorted-dict-items
+TESTS = {
+    "legacy_tool_provides_info_test": _legacy_tool_provides_info_test,
+}

tests/rule_based_toolchain/subjects.bzl

@@ -238,6 +238,7 @@ _ToolchainConfigFactory = generate_factory(
         allowlist_absolute_include_directories = ProviderDepset(_subjects.str),
         artifact_name_patterns = [],
         make_variables = [],
+        legacy_tools = _subjects.collection,
     ),
 )