fix(bazel): allow CustomProtoInfo in gapic_compat_proto_library (#18417)

In #17882
gapic_compat_proto_library was introduced to wrap srcs passed to
py_gapic_library and adapt modern @rules_proto StarlarkProtoInfo
(ProtoInfo) targets into CustomProtoInfo expected by
@rules_gapic//:gapic.bzl's proto_custom_library.

However, several targets pass `srcs = [":<api>_proto_with_info"]` (a
proto_library_with_info rule from @rules_gapic//:gapic.bzl which returns
CustomProtoInfo rather than StarlarkProtoInfo). Because
gapic_compat_proto_library strictly mandated `providers =
[StarlarkProtoInfo]`, Bazel analysis failed on those targets with:
`'<target>_proto_with_info' does not have mandatory providers:
'ProtoInfo'`.

Updated gapic_compat_proto_library_impl to check if CustomProtoInfo in
dep: and return [dep[DefaultInfo], dep[CustomProtoInfo]] directly
without re-wrapping.
Updated gapic_compat_proto_library attrs["dep"] to accept either
provider: providers = [[StarlarkProtoInfo], [CustomProtoInfo]].

Tested against several afflicted targets in googleapis manually and
running entire workspace presubmit in cl/983453303.

Fixes regression blocking b/559815865.

Author: noahdietz

packages/gapic-generator/rules_python_gapic/py_gapic.bzl

@@ -25,6 +25,11 @@ load("@rules_proto//proto:defs.bzl", StarlarkProtoInfo = "ProtoInfo")
 # into rules_gapic CustomProtoInfo provider required by proto_custom_library.
 def _gapic_compat_proto_library_impl(ctx):
     dep = ctx.attr.dep
+    if CustomProtoInfo in dep:
+        return [
+            dep[DefaultInfo],
+            dep[CustomProtoInfo],
+        ]
     starlark_proto = dep[StarlarkProtoInfo]
     return [
         dep[DefaultInfo],
@@ -41,7 +46,7 @@ def _gapic_compat_proto_library_impl(ctx):
 gapic_compat_proto_library = rule(
     implementation = _gapic_compat_proto_library_impl,
     attrs = {
-        "dep": attr.label(mandatory = True, providers = [StarlarkProtoInfo]),
+        "dep": attr.label(mandatory = True, providers = [[StarlarkProtoInfo], [CustomProtoInfo]]),
     }
 )