Plumbed copts (including the crucial -std=c99) to upb_proto_library() aspect.

BUILD

@@ -8,6 +8,7 @@ load(
     "upb_fasttable_enabled",
     "upb_proto_library",
     "upb_proto_reflection_library",
+    "upb_proto_library_copts",
 )
 
 # copybara:strip_for_google3_begin
@@ -36,6 +37,12 @@ upb_fasttable_enabled(
     visibility = ["//visibility:public"],
 )
 
+upb_proto_library_copts(
+    name = "upb_proto_library_copts__for_generated_code_only_do_not_use",
+    copts = UPB_DEFAULT_COPTS,
+    visibility = ["//visibility:public"],
+)
+
 # Public C/C++ libraries #######################################################
 
 cc_library(

bazel/upb_proto_library.bzl

@@ -52,7 +52,7 @@ def _filter_none(elems):
             out.append(elem)
     return out
 
-def _cc_library_func(ctx, name, hdrs, srcs, dep_ccinfos):
+def _cc_library_func(ctx, name, hdrs, srcs, copts, dep_ccinfos):
     """Like cc_library(), but callable from rules.
 
     Args:
@@ -88,6 +88,7 @@ def _cc_library_func(ctx, name, hdrs, srcs, dep_ccinfos):
         name = name,
         srcs = srcs,
         public_hdrs = hdrs,
+        user_compile_flags = copts,
         compilation_contexts = compilation_contexts,
         **blaze_only_args
     )
@@ -128,6 +129,22 @@ upb_fasttable_enabled = rule(
     build_setting = config.bool(flag = True)
 )
 
+# Dummy rule to expose select() copts to aspects  ##############################
+
+_UpbProtoLibraryCopts = provider(
+    fields = {
+        "copts": "copts for upb_proto_library()",
+    },
+)
+
+def upb_proto_library_copts_impl(ctx):
+    return _UpbProtoLibraryCopts(copts = ctx.attr.copts)
+
+upb_proto_library_copts = rule(
+    implementation = upb_proto_library_copts_impl,
+    attrs = {"copts": attr.string_list(default = [])},
+)
+
 # upb_proto_library / upb_proto_reflection_library shared code #################
 
 GeneratedSrcsInfo = provider(
@@ -223,6 +240,7 @@ def _upb_proto_aspect_impl(target, ctx, cc_provider, file_provider):
         name = ctx.rule.attr.name + ctx.attr._ext,
         hdrs = files.hdrs,
         srcs = files.srcs,
+        copts = ctx.attr._copts[_UpbProtoLibraryCopts].copts,
         dep_ccinfos = dep_ccinfos,
     )
     return [cc_provider(cc_info = cc_info), file_provider(srcs = files)]
@@ -246,6 +264,9 @@ def _maybe_add(d):
 
 _upb_proto_library_aspect = aspect(
     attrs = _maybe_add({
+        "_copts": attr.label(
+            default = "//:upb_proto_library_copts__for_generated_code_only_do_not_use",
+        ),
         "_upbc": attr.label(
             executable = True,
             cfg = "host",
@@ -292,6 +313,9 @@ upb_proto_library = rule(
 
 _upb_proto_reflection_library_aspect = aspect(
     attrs = _maybe_add({
+        "_copts": attr.label(
+            default = "//:upb_proto_library_copts__for_generated_code_only_do_not_use",
+        ),
         "_upbc": attr.label(
             executable = True,
             cfg = "host",

cmake/make_cmakelists.py

@@ -129,6 +129,9 @@ class BuildFileFunctions(object):
   def upb_proto_library(self, **kwargs):
     pass
 
+  def upb_proto_library_copts(self, **kwargs):
+    pass
+
   def upb_proto_reflection_library(self, **kwargs):
     pass