Tweak BUILD setup to make the layering check change less disruptive (#15838)

We recently updated the codebase to comply with the Bazel layering check, which
essentially requires any C++ header inclusion to be matched with a build
dependency on a target providing that header.

As part of that, I removed a handful of dependencies from the `//:protobuf`
target, since these dependencies were not set up in a way that respected the
layering check. However, I realized that this may cause a number of breakages,
especially since we did not provide the correct public targets until very
recently.

This change effectively adds back in the missing dependencies, so that projects
which do not yet adhere to the layering check can continue to depend on them
indirectly. This way, we still adhere to the layering check and make it
possible for projects that depend on us to do so, but in most cases we won't
immediately break anyone.

PiperOrigin-RevId: 607021111

Author: Adam Cozzette

BUILD.bazel

@@ -253,13 +253,13 @@ cc_binary(
 # a user-defined proto_lang_toolchain.
 alias(
     name = "protobuf",
-    actual = "//src/google/protobuf",
+    actual = "//src/google/protobuf:protobuf_layering_check_legacy",
     visibility = ["//visibility:public"],
 )
 
 alias(
     name = "protobuf_nowkt",
-    actual = "//src/google/protobuf:protobuf_nowkt",
+    actual = "//src/google/protobuf:protobuf_layering_check_legacy",
     deprecation = "Use //:protobuf instead",
     visibility = ["//visibility:public"],
 )

rust/cpp_kernel/BUILD

@@ -12,8 +12,8 @@ cc_library(
     ],
     deps = [
         ":rust_alloc_for_cpp_api",  # buildcleaner: keep
-        "//:protobuf",
-        "//:protobuf_lite",
+        "//src/google/protobuf",
+        "//src/google/protobuf:protobuf_lite",
         "@com_google_absl//absl/strings:string_view",
     ],
 )

src/google/protobuf/BUILD.bazel

@@ -515,6 +515,36 @@ cc_library(
     ],
 )
 
+PROTOBUF_HEADERS = [
+    "cpp_edition_defaults.h",
+    "cpp_features.pb.h",
+    "descriptor.h",
+    "descriptor.pb.h",
+    "descriptor_database.h",
+    "descriptor_visitor.h",
+    "dynamic_message.h",
+    "feature_resolver.h",
+    "field_access_listener.h",
+    "generated_enum_reflection.h",
+    "generated_message_bases.h",
+    "generated_message_reflection.h",
+    "generated_message_tctable_gen.h",
+    "internal_message_util.h",
+    "map_entry.h",
+    "map_field.h",
+    "map_field_inl.h",
+    "message.h",
+    "metadata.h",
+    "reflection.h",
+    "reflection_internal.h",
+    "reflection_mode.h",
+    "reflection_ops.h",
+    "service.h",
+    "text_format.h",
+    "unknown_field_set.h",
+    "wire_format.h",
+]
+
 cc_library(
     name = "protobuf",
     srcs = [
@@ -540,35 +570,7 @@ cc_library(
         "unknown_field_set.cc",
         "wire_format.cc",
     ],
-    hdrs = [
-        "cpp_edition_defaults.h",
-        "cpp_features.pb.h",
-        "descriptor.h",
-        "descriptor.pb.h",
-        "descriptor_database.h",
-        "descriptor_visitor.h",
-        "dynamic_message.h",
-        "feature_resolver.h",
-        "field_access_listener.h",
-        "generated_enum_reflection.h",
-        "generated_message_bases.h",
-        "generated_message_reflection.h",
-        "generated_message_tctable_gen.h",
-        "internal_message_util.h",
-        "map_entry.h",
-        "map_field.h",
-        "map_field_inl.h",
-        "message.h",
-        "metadata.h",
-        "reflection.h",
-        "reflection_internal.h",
-        "reflection_mode.h",
-        "reflection_ops.h",
-        "service.h",
-        "text_format.h",
-        "unknown_field_set.h",
-        "wire_format.h",
-    ],
+    hdrs = PROTOBUF_HEADERS,
     copts = COPTS,
     linkopts = LINK_OPTS,
     strip_include_prefix = "/src",
@@ -612,6 +614,44 @@ cc_library(
     ],
 )
 
+# This target exposes the headers for the protobuf runtime, and additionally
+# depends on the C++ well-known types and some other miscellaneous utilities.
+# The purpose is to preserve compatibility with projects that do not yet comply
+# with the layering check. Ideally everyone should get into compliance with the
+# layering check, which would mean for example taking a dependency on
+# //:any_cc_proto instead of relying on this target to make it available
+# indirectly.
+cc_library(
+    name = "protobuf_layering_check_legacy",
+    hdrs = PROTOBUF_HEADERS,
+    copts = COPTS,
+    linkopts = LINK_OPTS,
+    strip_include_prefix = "/src",
+    visibility = [
+        "//:__subpackages__",
+    ],
+    deps = [
+        ":any_cc_proto",
+        ":api_cc_proto",
+        ":duration_cc_proto",
+        ":empty_cc_proto",
+        ":field_mask_cc_proto",
+        ":protobuf",
+        ":source_context_cc_proto",
+        ":struct_cc_proto",
+        ":timestamp_cc_proto",
+        ":type_cc_proto",
+        ":wrappers_cc_proto",
+        "//src/google/protobuf/compiler:importer",
+        "//src/google/protobuf/util:delimited_message_util",
+        "//src/google/protobuf/util:differencer",
+        "//src/google/protobuf/util:field_mask_util",
+        "//src/google/protobuf/util:json_util",
+        "//src/google/protobuf/util:time_util",
+        "//src/google/protobuf/util:type_resolver",
+    ],
+)
+
 cc_test(
     name = "has_bits_test",
     srcs = ["has_bits_test.cc"],