Advertise CcInfo provider on rules (#2126)

The aspect used in the `cc_shared_library` implementation in bazel 6.3
and 7 only traverses attributes that advertise the `CcInfo` provider via
the `provides` attribute. This means in these versions of bazel, rust
libraries are currently omitted from libraries built with
`cc_shared_library`.

Fixes #2101.

.bazelrc

@@ -20,6 +20,10 @@ coverage --combined_report=lcov
 # https://bazel.build/reference/command-line-reference#flag--experimental_fetch_all_coverage_outputs
 coverage --experimental_fetch_all_coverage_outputs
 
+# Required for some of the tests
+# https://bazel.build/reference/command-line-reference#flag--experimental_cc_shared_library
+common --experimental_cc_shared_library
+
 ###############################################################################
 ## Unique configuration groups
 ###############################################################################

rust/private/rust.bzl

@@ -901,6 +901,7 @@ rust_static_library = rule(
         str(Label("//rust:toolchain_type")),
         "@bazel_tools//tools/cpp:toolchain_type",
     ],
+    provides = [CcInfo],
     doc = dedent("""\
         Builds a Rust static library.
 
@@ -948,6 +949,7 @@ rust_shared_library = rule(
         str(Label("//rust:toolchain_type")),
         "@bazel_tools//tools/cpp:toolchain_type",
     ],
+    provides = [CcInfo],
     doc = dedent("""\
         Builds a Rust shared library.
 

test/cc_shared_library/BUILD.bazel

@@ -0,0 +1,30 @@
+load("@rules_cc//cc:defs.bzl", "cc_library", "cc_test")
+load("@rules_rust//rust:defs.bzl", "rust_static_library")
+
+rust_static_library(
+    name = "rust_lib",
+    srcs = ["lib.rs"],
+    edition = "2021",
+)
+
+cc_library(
+    name = "c_lib",
+    srcs = ["lib.c"],
+    hdrs = ["lib.h"],
+    deps = [":rust_lib"],
+)
+
+# Tests that cc_shared_library correctly traverses into
+# `rust_static_library` when linking.
+cc_shared_library(
+    name = "shared",
+    deps = [":c_lib"],
+)
+
+cc_test(
+    name = "test",
+    srcs = ["main.c"],
+    dynamic_deps = [":shared"],
+    linkstatic = True,
+    deps = [":c_lib"],
+)

test/cc_shared_library/lib.c

@@ -0,0 +1,5 @@
+#include "lib.h"
+
+extern int32_t bar();
+
+int32_t foo() { return bar(); }

test/cc_shared_library/lib.h

@@ -0,0 +1,9 @@
+#include <stdint.h>
+
+#ifdef _WIN32
+#define DllExport __declspec(dllexport)
+#else
+#define DllExport
+#endif
+
+DllExport int32_t foo();

test/cc_shared_library/lib.rs

@@ -0,0 +1,4 @@
+#[no_mangle]
+pub extern "C" fn bar() -> i32 {
+    4
+}

test/cc_shared_library/main.c

@@ -0,0 +1,9 @@
+#include <assert.h>
+#include <stdint.h>
+
+#include "lib.h"
+
+int main(int argc, char** argv) {
+    assert(foo() == 4);
+    return 0;
+}