hpb_proto_library: properly handle alias libraries (srcs empty, reexport deps)

PiperOrigin-RevId: 689464159

hpb/bazel/hpb_proto_library.bzl

@@ -159,8 +159,6 @@ def _upb_cc_proto_rule_impl(ctx):
     ]
 
 def _upb_cc_proto_aspect_impl(target, ctx, cc_provider, file_provider):
-    proto_info = target[ProtoInfo]
-    files = _compile_upb_cc_protos(ctx, proto_info, proto_info.direct_sources)
     deps = ctx.rule.attr.deps + ctx.attr._upbprotos
     dep_ccinfos = [dep[CcInfo] for dep in deps if CcInfo in dep]
     dep_ccinfos += [dep[UpbWrappedCcInfo].cc_info for dep in deps if UpbWrappedCcInfo in dep]
@@ -168,15 +166,26 @@ def _upb_cc_proto_aspect_impl(target, ctx, cc_provider, file_provider):
     if UpbWrappedCcInfo not in target:
         fail("Target should have UpbWrappedCcInfo provider")
     dep_ccinfos.append(target[UpbWrappedCcInfo].cc_info)
-    cc_info = _cc_library_func(
-        ctx = ctx,
-        name = ctx.rule.attr.name + ".upbprotos",
-        hdrs = files.hdrs,
-        srcs = files.srcs,
-        copts = ctx.attr._ccopts[HpbProtoLibraryCoptsInfo].copts,
-        dep_ccinfos = dep_ccinfos,
-    )
-    return [cc_provider(cc_info = cc_info), file_provider(srcs = files)]
+    proto_info = target[ProtoInfo]
+
+    if not getattr(ctx.rule.attr, "srcs", []):
+        # This target doesn't declare any sources, reexport all its deps instead.
+        # This is known as an "alias library":
+        # https://bazel.build/versions/6.4.0/reference/be/protocol-buffer#proto_library.srcs
+        return [cc_provider(
+            cc_info = cc_common.merge_cc_infos(direct_cc_infos = dep_ccinfos),
+        ), file_provider(srcs = GeneratedSrcsInfo(srcs = [], hdrs = []))]
+    else:
+        files = _compile_upb_cc_protos(ctx, proto_info, proto_info.direct_sources)
+        cc_info = _cc_library_func(
+            ctx = ctx,
+            name = ctx.rule.attr.name + ".upbprotos",
+            hdrs = files.hdrs,
+            srcs = files.srcs,
+            copts = ctx.attr._ccopts[HpbProtoLibraryCoptsInfo].copts,
+            dep_ccinfos = dep_ccinfos,
+        )
+        return [cc_provider(cc_info = cc_info), file_provider(srcs = files)]
 
 def _upb_cc_proto_library_aspect_impl(target, ctx):
     return _upb_cc_proto_aspect_impl(target, ctx, _UpbCcWrappedCcInfo, _WrappedCcGeneratedSrcsInfo)

hpb_generator/tests/test_hpb_bzl_alias.cc

@@ -0,0 +1,22 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2024 Google LLC.  All rights reserved.
+//
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file or at
+// https://developers.google.com/open-source/licenses/bsd
+
+#include <gtest/gtest.h>
+#include "google/protobuf/compiler/hpb/tests/set_alias.upb.proto.h"
+#include "google/protobuf/hpb/arena.h"
+#include "google/protobuf/hpb/hpb.h"
+
+namespace {
+using hpb_unittest::protos::Child;
+
+TEST(BzlCode, CheckBzlAlias) {
+  hpb::Arena arena;
+  auto child = hpb::CreateMessage<Child>(arena);
+  child.set_peeps(12);
+  ASSERT_EQ(child.peeps(), 12);
+}
+}  // namespace