Refactor proto toolchainsation support utilities

Implement reusable utils as part of proto_common and move out of semantics. Define toolchains that will be needed for lang_proto_libraries.

Because there are so many toolchains this will make the future code more readable.

Issue: bazelbuild/rules_proto#179
PiperOrigin-RevId: 570019432
Change-Id: Ie1675f1d847872bab3a250270eaa451ef4816ed8

src/main/starlark/builtins_bzl/common/proto/proto_common.bzl

@@ -265,6 +265,34 @@ def _declare_generated_files(
 
     return outputs
 
+def _find_toolchain(ctx, legacy_attr, toolchain_type):
+    if _builtins.toplevel.proto_common.incompatible_enable_proto_toolchain_resolution():
+        toolchain = ctx.toolchains[toolchain_type]
+        if not toolchain:
+            fail("No toolchains registered for '%s'." % toolchain_type)
+        return toolchain.proto
+    else:
+        return getattr(ctx.attr, legacy_attr)[ProtoLangToolchainInfo]
+
+def _use_toolchain(toolchain_type):
+    if _builtins.toplevel.proto_common.incompatible_enable_proto_toolchain_resolution():
+        return [_builtins.toplevel.config_common.toolchain_type(toolchain_type, mandatory = False)]
+    else:
+        return []
+
+def _if_legacy_toolchain(legacy_attr_dict):
+    if _builtins.toplevel.proto_common.incompatible_enable_proto_toolchain_resolution():
+        return {}
+    else:
+        return legacy_attr_dict
+
+toolchains = struct(
+    use_toolchain = _use_toolchain,
+    find_toolchain = _find_toolchain,
+    if_legacy_toolchain = _if_legacy_toolchain,
+    INCOMPATIBLE_ENABLE_PROTO_TOOLCHAIN_RESOLUTION = _builtins.toplevel.proto_common.incompatible_enable_proto_toolchain_resolution(),
+)
+
 proto_common_do_not_use = struct(
     compile = _compile,
     declare_generated_files = _declare_generated_files,

src/main/starlark/builtins_bzl/common/proto/proto_lang_toolchain.bzl

@@ -14,7 +14,7 @@
 
 """A Starlark implementation of the proto_lang_toolchain rule."""
 
-load(":common/proto/proto_common.bzl", "ProtoLangToolchainInfo")
+load(":common/proto/proto_common.bzl", "ProtoLangToolchainInfo", "toolchains")
 load(":common/proto/proto_semantics.bzl", "semantics")
 
 ProtoInfo = _builtins.toplevel.ProtoInfo
@@ -31,9 +31,9 @@ def _rule_impl(ctx):
     if ctx.attr.plugin != None:
         plugin = ctx.attr.plugin[DefaultInfo].files_to_run
 
-    if semantics.INCOMPATIBLE_ENABLE_PROTO_TOOLCHAIN_RESOLUTION:
-        proto_compiler = ctx.toolchains[semantics.PROTO_TOOLCHAIN_TYPE].proto.proto_compiler
-        protoc_opts = ctx.toolchains[semantics.PROTO_TOOLCHAIN_TYPE].proto.protoc_opts
+    if toolchains.INCOMPATIBLE_ENABLE_PROTO_TOOLCHAIN_RESOLUTION:
+        proto_compiler = ctx.toolchains[semantics.PROTO_TOOLCHAIN].proto.proto_compiler
+        protoc_opts = ctx.toolchains[semantics.PROTO_TOOLCHAIN].proto.protoc_opts
     else:
         proto_compiler = ctx.attr._proto_compiler.files_to_run
         protoc_opts = ctx.fragments.proto.experimental_protoc_opts
@@ -74,7 +74,7 @@ proto_lang_toolchain = rule(
             "blacklisted_protos": attr.label_list(
                 providers = [ProtoInfo],
             ),
-        } | ({} if semantics.INCOMPATIBLE_ENABLE_PROTO_TOOLCHAIN_RESOLUTION else {
+        } | ({} if toolchains.INCOMPATIBLE_ENABLE_PROTO_TOOLCHAIN_RESOLUTION else {
             "_proto_compiler": attr.label(
                 cfg = "exec",
                 executable = True,
@@ -84,5 +84,5 @@ proto_lang_toolchain = rule(
         }),
     provides = [ProtoLangToolchainInfo],
     fragments = ["proto"],
-    toolchains = semantics.PROTO_TOOLCHAIN,  # Used to obtain protoc
+    toolchains = toolchains.use_toolchain(semantics.PROTO_TOOLCHAIN),  # Used to obtain protoc
 )

src/main/starlark/builtins_bzl/common/proto/proto_library.bzl

@@ -16,8 +16,8 @@
 Definition of proto_library rule.
 """
 
+load(":common/proto/proto_common.bzl", "toolchains", proto_common = "proto_common_do_not_use")
 load(":common/proto/proto_semantics.bzl", "semantics")
-load(":common/proto/proto_common.bzl", proto_common = "proto_common_do_not_use")
 load(":common/paths.bzl", "paths")
 
 ProtoInfo = _builtins.toplevel.ProtoInfo
@@ -251,8 +251,8 @@ def _write_descriptor_set(ctx, direct_sources, deps, exports, proto_info, descri
             args.add("--allowed_public_imports=")
         else:
             args.add_joined("--allowed_public_imports", public_import_protos, map_each = _get_import_path, join_with = ":")
-    if semantics.INCOMPATIBLE_ENABLE_PROTO_TOOLCHAIN_RESOLUTION:
-        toolchain = ctx.toolchains[semantics.PROTO_TOOLCHAIN_TYPE]
+    if toolchains.INCOMPATIBLE_ENABLE_PROTO_TOOLCHAIN_RESOLUTION:
+        toolchain = ctx.toolchains[semantics.PROTO_TOOLCHAIN]
         if not toolchain:
             fail("Protocol compiler toolchain could not be resolved.")
         proto_lang_toolchain_info = toolchain.proto
@@ -295,7 +295,7 @@ proto_library = rule(
             flags = ["SKIP_CONSTRAINTS_OVERRIDE"],
         ),
         "licenses": attr.license() if hasattr(attr, "license") else attr.string_list(),
-    } | ({} if semantics.INCOMPATIBLE_ENABLE_PROTO_TOOLCHAIN_RESOLUTION else {
+    } | toolchains.if_legacy_toolchain({
         "_proto_compiler": attr.label(
             cfg = "exec",
             executable = True,
@@ -306,5 +306,5 @@ proto_library = rule(
     fragments = ["proto"] + semantics.EXTRA_FRAGMENTS,
     provides = [ProtoInfo],
     output_to_genfiles = True,  # TODO(b/204266604) move to bin dir
-    toolchains = semantics.PROTO_TOOLCHAIN,
+    toolchains = toolchains.use_toolchain(semantics.PROTO_TOOLCHAIN),
 )

src/main/starlark/builtins_bzl/common/proto/proto_semantics.bzl

@@ -19,18 +19,8 @@ Proto Semantics
 def _preprocess(ctx):
     pass
 
-_PROTO_TOOLCHAIN_TYPE = "@rules_proto//proto:toolchain_type"
-
-def _get_proto_toolchain():
-    if _builtins.toplevel.proto_common.incompatible_enable_proto_toolchain_resolution():
-        return [_builtins.toplevel.config_common.toolchain_type(_PROTO_TOOLCHAIN_TYPE, mandatory = False)]
-    else:
-        return []
-
 semantics = struct(
-    PROTO_TOOLCHAIN_TYPE = _PROTO_TOOLCHAIN_TYPE,
-    PROTO_TOOLCHAIN = _get_proto_toolchain(),
-    INCOMPATIBLE_ENABLE_PROTO_TOOLCHAIN_RESOLUTION = _builtins.toplevel.proto_common.incompatible_enable_proto_toolchain_resolution(),
+    PROTO_TOOLCHAIN = "@rules_proto//proto:toolchain_type",
     PROTO_COMPILER_LABEL = "@bazel_tools//tools/proto:protoc",
     EXTRA_ATTRIBUTES = {
         "import_prefix": attr.string(),