Make labels relative

Prepare protobuf for bzlmod

Self-reference to `@com_google_protobuf` doesn't work with bzlmod.

In case this is a rule attribute, no reference is needed.

When the label is a default parameter value in a macro it needs to be wrapped with `Label` call, to relativise it correctly.

PiperOrigin-RevId: 496687786

BUILD.bazel

@@ -306,8 +306,8 @@ alias(
 proto_lang_toolchain(
     name = "cc_toolchain",
     blacklisted_protos = [
-        "@com_google_protobuf//:compiler_plugin_proto",
-        "@com_google_protobuf//:descriptor_proto",
+        "//:compiler_plugin_proto",
+        "//:descriptor_proto",
     ],
     command_line = "--cpp_out=$(OUT)",
     runtime = ":protobuf",

protobuf.bzl

@@ -328,7 +328,7 @@ internal_gen_well_known_protos_java = rule(
         "_protoc": attr.label(
             executable = True,
             cfg = "exec",
-            default = "@com_google_protobuf//:protoc",
+            default = "//:protoc",
         ),
     },
 )
@@ -402,8 +402,8 @@ def internal_objc_proto_library(
         outs = [],
         proto_deps = [],
         includes = ["."],
-        default_runtime = "@com_google_protobuf//:protobuf_objc",
-        protoc = "@com_google_protobuf//:protoc",
+        default_runtime = Label("//:protobuf_objc"),
+        protoc = Label("//:protoc"),
         testonly = None,
         visibility = ["//visibility:public"],
         **kwargs):
@@ -485,6 +485,15 @@ def internal_objc_proto_library(
         **kwargs
     )
 
+# When canonical labels are in use, use additional "@" prefix
+_canonical_label_prefix = "@" if str(Label("//:protoc")).startswith("@@") else ""
+
+def _to_label(label_str):
+    """Converts a string to a label using the repository of the calling thread"""
+    if type(label_str) == type(Label("//:foo")):
+        return label_str
+    return Label(_canonical_label_prefix + native.repository_name() + "//" + native.package_name() + ":foo").relative(label_str)
+
 def internal_py_proto_library(
         name,
         srcs = [],
@@ -492,8 +501,8 @@ def internal_py_proto_library(
         py_libs = [],
         py_extra_srcs = [],
         include = None,
-        default_runtime = "@com_google_protobuf//:protobuf_python",
-        protoc = "@com_google_protobuf//:protoc",
+        default_runtime = Label("//:protobuf_python"),
+        protoc = Label("//:protoc"),
         use_grpc_plugin = False,
         testonly = None,
         **kargs):
@@ -546,8 +555,12 @@ def internal_py_proto_library(
         plugin_language = "grpc",
     )
 
-    if default_runtime and not default_runtime in py_libs + deps:
+    if default_runtime:
+        # Resolve non-local labels
+        labels = [_to_label(lib) for lib in py_libs + deps]
+        if not _to_label(default_runtime) in labels:
             py_libs = py_libs + [default_runtime]
+
     py_library(
         name = name,
         testonly = testonly,
@@ -580,7 +593,7 @@ def _source_proto_library(
         outs = [],
         lang = None,
         includes = ["."],
-        protoc = "@com_google_protobuf//:protoc",
+        protoc = Label("//:protoc"),
         testonly = None,
         visibility = ["//visibility:public"],
         **kwargs):

protobuf_deps.bzl

@@ -48,7 +48,7 @@ def protobuf_deps():
     if not native.existing_rule("zlib"):
         http_archive(
             name = "zlib",
-            build_file = "@com_google_protobuf//:third_party/zlib.BUILD",
+            build_file = "//:third_party/zlib.BUILD",
             sha256 = "d14c38e313afc35a9a8760dadf26042f51ea0f5d154b0630a31da0540107fb98",
             strip_prefix = "zlib-1.2.13",
             urls = [
@@ -60,7 +60,7 @@ def protobuf_deps():
     if not native.existing_rule("jsoncpp"):
         http_archive(
             name = "jsoncpp",
-            build_file = "@com_google_protobuf//:third_party/jsoncpp.BUILD",
+            build_file = "//:third_party/jsoncpp.BUILD",
             sha256 = "e34a628a8142643b976c7233ef381457efad79468c67cb1ae0b83a33d7493999",
             strip_prefix = "jsoncpp-1.9.4",
             urls = ["https://github.com/open-source-parsers/jsoncpp/archive/refs/tags/1.9.4.tar.gz"],