Move py_proto_library toolchain into protobuf repository.

PiperOrigin-RevId: 671292735

bazel/private/BUILD

@@ -7,6 +7,11 @@ toolchain_type(
     name = "proto_toolchain_type",
 )
 
+toolchain_type(
+    name = "python_toolchain_type",
+    visibility = ["//visibility:public"],
+)
+
 bzl_library(
     name = "upb_proto_library_internal_bzl",
     srcs = [

bazel/py_proto_library.bzl

@@ -5,7 +5,7 @@ load("//bazel/common:proto_common.bzl", "proto_common")
 load("//bazel/common:proto_info.bzl", "ProtoInfo")
 load("//bazel/private:toolchain_helpers.bzl", "toolchains")
 
-PY_PROTO_TOOLCHAIN = "@rules_python//python/proto:toolchain_type"
+_PY_PROTO_TOOLCHAIN = Label("//bazel/private:python_toolchain_type")
 
 _PyProtoInfo = provider(
     doc = "Encapsulates information needed by the Python proto rules.",
@@ -50,9 +50,9 @@ def _py_proto_aspect_impl(target, ctx):
             ))
 
     if proto_common.INCOMPATIBLE_ENABLE_PROTO_TOOLCHAIN_RESOLUTION:
-        toolchain = ctx.toolchains[PY_PROTO_TOOLCHAIN]
+        toolchain = ctx.toolchains[_PY_PROTO_TOOLCHAIN]
         if not toolchain:
-            fail("No toolchains registered for '%s'." % PY_PROTO_TOOLCHAIN)
+            fail("No toolchains registered for '%s'." % _PY_PROTO_TOOLCHAIN)
         proto_lang_toolchain_info = toolchain.proto
     else:
         proto_lang_toolchain_info = getattr(ctx.attr, "_aspect_proto_toolchain")[proto_common.ProtoLangToolchainInfo]
@@ -126,7 +126,7 @@ _py_proto_aspect = aspect(
     attr_aspects = ["deps"],
     required_providers = [ProtoInfo],
     provides = [_PyProtoInfo],
-    toolchains = toolchains.use_toolchain(PY_PROTO_TOOLCHAIN),
+    toolchains = toolchains.use_toolchain(_PY_PROTO_TOOLCHAIN),
 )
 
 def _py_proto_library_rule(ctx):