Only respect the Starlark versions of --proto_toolchain_for*. This is a breaking change. (#26067)

PiperOrigin-RevId: 873037670

Co-authored-by: Protobuf Team Bot <protobuf-github-bot@google.com>

bazel/flags/flags.bzl

diff --git a/bazel/flags/flags.bzl b/bazel/flags/flags.bzl
index 4823e24..c20080c 100644
--- a/bazel/flags/flags.bzl
+++ b/bazel/flags/flags.bzl
@@ -36,16 +36,16 @@
         default = [".pb.cc"],
     ),
     "proto_toolchain_for_java": struct(
-        native = lambda ctx: getattr(ctx.attr, "_aspect_java_proto_toolchain"),
-        default = "@bazel_tools//tools/proto:java_toolchain",
+        native = lambda ctx: "//:java_toolchain",
+        default = "//:java_toolchain",
     ),
     "proto_toolchain_for_javalite": struct(
-        native = lambda ctx: getattr(ctx.attr, "_aspect_proto_toolchain_for_javalite"),
-        default = "@bazel_tools//tools/proto:javalite_toolchain",
+        native = lambda ctx: "//:javalite_toolchain",
+        default = "//:javalite_toolchain",
     ),
     "proto_toolchain_for_cc": struct(
-        native = lambda ctx: getattr(ctx.attr, "_aspect_cc_proto_toolchain"),
-        default = "@bazel_tools//tools/proto:cc_toolchain",
+        native = lambda ctx: "//:cc_toolchain",
+        default = "//:cc_toolchain",
     ),
 }
 

bazel/private/java_lite_proto_library.bzl

diff --git a/bazel/private/java_lite_proto_library.bzl b/bazel/private/java_lite_proto_library.bzl
index 0f22290..af7ca14 100644
--- a/bazel/private/java_lite_proto_library.bzl
+++ b/bazel/private/java_lite_proto_library.bzl
@@ -72,9 +72,6 @@
     implementation = _aspect_impl,
     attr_aspects = ["deps", "exports"],
     attrs = toolchains.if_legacy_toolchain({
-        _PROTO_TOOLCHAIN_ATTR: attr.label(
-            default = configuration_field(fragment = "proto", name = "proto_toolchain_for_java_lite"),
-        ),
         "_proto_toolchain_for_javalite": attr.label(
             default = Label("//bazel/flags/java:proto_toolchain_for_javalite"),
         ),
@@ -171,9 +168,6 @@
 rules to generate Java code for.
 """),
     } | toolchains.if_legacy_toolchain({
-        _PROTO_TOOLCHAIN_ATTR: attr.label(
-            default = configuration_field(fragment = "proto", name = "proto_toolchain_for_java_lite"),
-        ),
         "_proto_toolchain_for_javalite": attr.label(
             default = Label("//bazel/flags/java:proto_toolchain_for_javalite"),
         ),

bazel/private/java_proto_library.bzl

diff --git a/bazel/private/java_proto_library.bzl b/bazel/private/java_proto_library.bzl
index 7b2f869..b0dd56d 100644
--- a/bazel/private/java_proto_library.bzl
+++ b/bazel/private/java_proto_library.bzl
@@ -73,9 +73,6 @@
     implementation = _java_proto_aspect_impl,
     attrs = (
         toolchains.if_legacy_toolchain({
-            "_aspect_java_proto_toolchain": attr.label(
-                default = configuration_field(fragment = "proto", name = "proto_toolchain_for_java"),
-            ),
             "_proto_toolchain_for_java": attr.label(
                 default = "//bazel/flags/java:proto_toolchain_for_java",
             ),
@@ -163,9 +160,6 @@
         # buildifier: disable=attr-license (calling attr.license())
         "licenses": attr.license() if hasattr(attr, "license") else attr.string_list(),
     } | toolchains.if_legacy_toolchain({
-        "_aspect_java_proto_toolchain": attr.label(
-            default = configuration_field(fragment = "proto", name = "proto_toolchain_for_java"),
-        ),
         "_proto_toolchain_for_java": attr.label(
             default = "//bazel/flags/java:proto_toolchain_for_java",
         ),

bazel/private/oss/cc_proto_library.bzl

diff --git a/bazel/private/oss/cc_proto_library.bzl b/bazel/private/oss/cc_proto_library.bzl
index d230941..3d4444c 100644
--- a/bazel/private/oss/cc_proto_library.bzl
+++ b/bazel/private/oss/cc_proto_library.bzl
@@ -125,9 +125,6 @@
                 ),
             } |
             toolchains.if_legacy_toolchain({
-                "_aspect_cc_proto_toolchain": attr.label(
-                    default = configuration_field(fragment = "proto", name = "proto_toolchain_for_cc"),
-                ),
                 "_proto_toolchain_for_cc": attr.label(
                     default = Label("//bazel/flags/cc:proto_toolchain_for_cc"),
                 ),
@@ -196,9 +193,6 @@
 rules to generate C++ code for.""",
         ),
     } | toolchains.if_legacy_toolchain({
-        "_aspect_cc_proto_toolchain": attr.label(
-            default = configuration_field(fragment = "proto", name = "proto_toolchain_for_cc"),
-        ),
         "_proto_toolchain_for_cc": attr.label(
             default = "//bazel/flags/cc:proto_toolchain_for_cc",
         ),

bazel/private/proto_lang_toolchain_rule.bzl

diff --git a/bazel/private/proto_lang_toolchain_rule.bzl b/bazel/private/proto_lang_toolchain_rule.bzl
index 8c63806..0e7da9e 100644
--- a/bazel/private/proto_lang_toolchain_rule.bzl
+++ b/bazel/private/proto_lang_toolchain_rule.bzl
@@ -154,10 +154,7 @@
         ),
     } | ({} if proto_common.INCOMPATIBLE_ENABLE_PROTO_TOOLCHAIN_RESOLUTION else {
         "_proto_compiler": attr.label(
-            cfg = "exec",
-            executable = True,
-            allow_files = True,
-            default = configuration_field("proto", "proto_compiler"),
+            default = "//bazel/flags:proto_compiler",
         ),
     }),
     provides = [ProtoLangToolchainInfo],