Make cc_library(alwayslink=True) apply to .a in srcs

Previously if you had an archive in the srcs of a cc_library and set
alwayslink=True that was ignored. You had to have named the library .lo
(arguably an implementation detail) to get the desired behavior.

Author: keith

cc/private/rules_impl/cc_library.bzl

@@ -194,6 +194,7 @@ def _cc_library_impl(ctx):
         feature_configuration,
         ctx.fragments.cpp.force_pic(),
         precompiled_files,
+        ctx.attr.alwayslink,
     )
 
     if not cc_helper.is_compilation_outputs_empty(compilation_outputs):
@@ -373,7 +374,8 @@ def _convert_precompiled_libraries_to_library_to_link(
         cc_toolchain,
         feature_configuration,
         force_pic,
-        precompiled_files):
+        precompiled_files,
+        alwayslink):
     static_libraries = _build_map_identifier_to_artifact(precompiled_files[2])
     pic_static_libraries = _build_map_identifier_to_artifact(precompiled_files[3])
     alwayslink_static_libraries = _build_map_identifier_to_artifact(precompiled_files[4])
@@ -413,7 +415,7 @@ def _convert_precompiled_libraries_to_library_to_link(
             static_library = static_library,
             pic_static_library = pic_static_library,
             dynamic_library = dynamic_library,
-            alwayslink = identifier in alwayslink_static_libraries,
+            alwayslink = alwayslink or identifier in alwayslink_static_libraries,
         )
         libraries.append(library)
 
@@ -435,7 +437,7 @@ def _convert_precompiled_libraries_to_library_to_link(
             feature_configuration = feature_configuration,
             cc_toolchain = cc_toolchain,
             pic_static_library = pic_static_library,
-            alwayslink = identifier in alwayslink_static_libraries,
+            alwayslink = alwayslink or identifier in alwayslink_static_libraries,
         )
         libraries.append(library)
 

tests/alwayslink_srcs/BUILD

@@ -0,0 +1,62 @@
+# 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.
+
+load("//cc:cc_library.bzl", "cc_library")
+load("//cc:cc_test.bzl", "cc_test")
+
+licenses(["notice"])
+
+# Library that provides the registration state (was_registered/set_registered).
+cc_library(
+    name = "registered",
+    srcs = ["registered.c"],
+    hdrs = ["registered.h"],
+)
+
+# Library that registers itself via a static constructor.
+cc_library(
+    name = "registerer_lib",
+    srcs = ["registerer.c"],
+    deps = [":registered"],
+)
+
+# Copy the .a file produced by registerer_lib, simulates having a prebuilt .a file.
+genrule(
+    name = "copy_registerer_archive",
+    srcs = [":registerer_lib"],
+    outs = ["libregisterer_copied.a"],
+    cmd = "for f in $(locations :registerer_lib); do if [[ $$f == *.a ]]; then cp $$f $@; fi; done",
+)
+
+# Library that uses the copied .a file in srcs with alwayslink=True.
+# Without alwayslink, the registerer would be dropped since nothing
+# directly references its symbols.
+cc_library(
+    name = "registerer_alwayslink",
+    srcs = [":copy_registerer_archive"],
+    deps = [":registered"],
+    alwayslink = True,
+)
+
+# Test that verifies the symbol was loaded at runtime.
+# The test does not directly reference any symbol from registerer,
+# so without alwayslink the static constructor would not run.
+cc_test(
+    name = "alwayslink_test",
+    srcs = ["alwayslink_test.c"],
+    deps = [
+        ":registered",
+        ":registerer_alwayslink",
+    ],
+)

tests/alwayslink_srcs/alwayslink_test.c

@@ -0,0 +1,29 @@
+// 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.
+
+#include <stdio.h>
+
+#include "tests/alwayslink_srcs/registered.h"
+
+int main(void) {
+  // If alwayslink worked correctly, the registerer library should have been
+  // linked even though nothing directly references its symbols. The static
+  // constructor should have called set_registered().
+  if (!was_registered()) {
+    fprintf(stderr, "FAILED: alwayslink did not work - static constructor was not executed\n");
+    return 1;
+  }
+  printf("PASSED: alwayslink worked - static constructor was executed\n");
+  return 0;
+}

tests/alwayslink_srcs/registered.c

@@ -0,0 +1,21 @@
+// 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.
+
+#include "tests/alwayslink_srcs/registered.h"
+
+static int g_registered = 0;
+
+int was_registered(void) { return g_registered; }
+
+void set_registered(void) { g_registered = 1; }

tests/alwayslink_srcs/registered.h

@@ -0,0 +1,24 @@
+// 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.
+
+#ifndef TESTS_ALWAYSLINK_SRCS_REGISTERED_H_
+#define TESTS_ALWAYSLINK_SRCS_REGISTERED_H_
+
+// Returns 1 if the registerer constructor was executed.
+int was_registered(void);
+
+// Called by the registerer's constructor.
+void set_registered(void);
+
+#endif  // TESTS_ALWAYSLINK_SRCS_REGISTERED_H_

tests/alwayslink_srcs/registerer.c

@@ -0,0 +1,20 @@
+// 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.
+
+#include "tests/alwayslink_srcs/registered.h"
+
+// Static constructor that registers on load.
+__attribute__((constructor)) static void registerer_init(void) {
+  set_registered();
+}