Use the toolchain protoc by default in internal rules.

#test-continuous

While we'd like to burn these down, they're still necessary at least for WKT to avoid cyclic dependencies.  This solution at least enabled prebuilt protoc for languages other than Java/Kotlin.

Fixes #25453

PiperOrigin-RevId: 862290462

Author: mkruskal-google

BUILD.bazel

@@ -671,7 +671,6 @@ internal_py_proto_library(
     testonly = 1,
     srcs = [":generated_protos"],
     default_runtime = "",
-    protoc = ":protoc",
     deps = ["//python:python_common_test_protos"],
 )
 

protobuf.bzl

@@ -195,7 +195,8 @@ def _proto_gen_impl(ctx):
         generated_files.extend(outs)
 
         inputs = [src] + deps.to_list()
-        tools = [ctx.executable.protoc]
+        protoc = ctx.executable.protoc or _protoc_files_to_run(ctx)
+        tools = [protoc]
         if ctx.executable.plugin:
             plugin = ctx.executable.plugin
             lang = ctx.attr.plugin_language
@@ -218,14 +219,14 @@ def _proto_gen_impl(ctx):
                 tools = tools,
                 outputs = outs,
                 arguments = args + import_flags.to_list() + [src.path],
-                executable = ctx.executable.protoc,
+                executable = protoc,
                 mnemonic = "ProtoCompile",
                 use_default_shell_env = True,
             )
         else:
             for out in outs:
                 orig_command = " ".join(
-                    ["$(realpath %s)" % ctx.executable.protoc.path] + args +
+                    ["$(realpath %s)" % protoc.path] + args +
                     import_flags_real + [src.basename],
                 )
                 command = ";".join([
@@ -267,7 +268,6 @@ Args:
   deps: a list of dependency labels; must be other proto libraries.
   enable_editions: if true, sets the --experimental_editions flag.
   includes: a list of include paths to .proto files.
-  protoc: the label of the protocol compiler to generate the sources.
   plugin: the label of the protocol compiler plugin to be passed to the protocol
     compiler.
   plugin_language: the language of the generated sources
@@ -288,7 +288,7 @@ _proto_gen = rule(
             cfg = "exec",
             executable = True,
             allow_single_file = True,
-            mandatory = True,
+            mandatory = False,
         ),
         "plugin": attr.label(
             cfg = "exec",
@@ -302,8 +302,10 @@ _proto_gen = rule(
         "out_type": attr.string(
             default = "all",
         ),
-    },
+    } | _PROTOC_ATTRS,
     implementation = _proto_gen_impl,
+    fragments = _PROTOC_FRAGMENTS,
+    toolchains = _PROTOC_TOOLCHAINS,
 )
 
 def _internal_gen_well_known_protos_java_impl(ctx):
@@ -434,7 +436,7 @@ def internal_objc_proto_library(
         proto_deps = [],
         includes = ["."],
         default_runtime = Label("//:protobuf_objc"),
-        protoc = Label("//:protoc"),
+        protoc = None,
         testonly = None,
         visibility = ["//visibility:public"],
         **kwargs):
@@ -522,7 +524,7 @@ def internal_ruby_proto_library(
         deps = [],
         includes = ["."],
         default_runtime = "@com_google_protobuf//ruby:protobuf",
-        protoc = "@com_google_protobuf//:protoc",
+        protoc = None,
         testonly = None,
         visibility = ["//visibility:public"],
         **kwargs):
@@ -577,7 +579,7 @@ def internal_rbs_proto_library(
         srcs = [],
         deps = [],
         includes = ["."],
-        protoc = "@com_google_protobuf//:protoc",
+        protoc = None,
         testonly = None,
         visibility = ["//visibility:public"],
         **kwargs):
@@ -640,7 +642,7 @@ def internal_py_proto_library(
         py_extra_srcs = [],
         include = None,
         default_runtime = Label("//:protobuf_python"),
-        protoc = Label("//:protoc"),
+        protoc = None,
         use_grpc_plugin = False,
         testonly = None,
         **kargs):
@@ -716,7 +718,7 @@ def _source_proto_library(
         outs = [],
         lang = None,
         includes = ["."],
-        protoc = Label("//:protoc"),
+        protoc = None,
         testonly = None,
         visibility = ["//visibility:public"],
         enable_editions = False,

python/build_targets.bzl

@@ -55,7 +55,6 @@ def build_targets(name):
         srcs = [":copied_wkt_proto_files"],
         include = ".",
         default_runtime = "",
-        protoc = "//:protoc",
         srcs_version = "PY2AND3",
         visibility = [
             "//:__pkg__",
@@ -291,7 +290,6 @@ def build_targets(name):
         ],
         include = ".",
         default_runtime = "",
-        protoc = "//:protoc",
         srcs_version = "PY2AND3",
         visibility = [
             "//:__pkg__",
@@ -306,7 +304,6 @@ def build_targets(name):
         srcs = [":copied_test_proto_files"],
         include = ".",
         default_runtime = "",
-        protoc = "//:protoc",
         srcs_version = "PY2AND3",
         visibility = ["//:__pkg__"],
         deps = [":well_known_types_py_pb2", ":test_dependency_proto_py_pb2"],
@@ -321,7 +318,6 @@ def build_targets(name):
         ]),
         include = ".",
         default_runtime = ":protobuf_python",
-        protoc = "//:protoc",
         srcs_version = "PY2AND3",
         visibility = ["//:__pkg__"],
         deps = [":python_common_test_protos"],
@@ -333,7 +329,6 @@ def build_targets(name):
         srcs = [":copied_conformance_test_files"],
         include = ".",
         default_runtime = "//:protobuf_python",
-        protoc = "//:protoc",
         visibility = [
             "//conformance:__pkg__",
             "//python:__subpackages__",