Revert "Manually register the Twirl compiler toolchain"

This reverts commit 1379dc6.

MODULE.bazel

@@ -22,8 +22,6 @@ register_toolchains(
     "//:repository_default_toolchain_21_definition",
     "//scala:zinc_2_13",
     "//scala:zinc_3",
-    "//twirl-toolchain:twirl-2-13",
-    "//twirl-toolchain:twirl-3",
 )
 
 # Please ensure these stay up-to-date with the versions in `versions.bzl`. Unfortunately,

WORKSPACE

@@ -0,0 +1,6 @@
+workspace(name = "rules_twirl")
+
+# Twirl compiler
+load("//twirl-toolchain:register-toolchains.bzl", "twirl_register_toolchains")
+
+twirl_register_toolchains(default_toolchain_name = "twirl-3")

twirl-toolchain/BUILD.bazel

@@ -1,21 +1,8 @@
 load("@bazel_skylib//:bzl_library.bzl", "bzl_library")
-load("@bazel_skylib//rules:common_settings.bzl", "string_flag", "string_setting")
 load(":create-toolchain.bzl", "create_twirl_toolchain")
 
 toolchain_type(name = "toolchain_type")
 
-string_setting(
-    name = "original-twirl-toolchain",
-    build_setting_default = "",
-    visibility = ["//visibility:public"],
-)
-
-string_flag(
-    name = "twirl-toolchain",
-    build_setting_default = "twirl-3",
-    visibility = ["//visibility:public"],
-)
-
 create_twirl_toolchain(
     name = "twirl-3",
     twirl_compiler = "//twirl-compiler-cli:twirl-compiler-cli-3",

twirl-toolchain/create-toolchain.bzl

@@ -12,7 +12,7 @@ def create_twirl_toolchain(name, twirl_compiler):
     native.config_setting(
         name = config_setting_name,
         flag_values = {
-            "//twirl-toolchain": name,
+            "@rules_twirl_toolchain//:twirl-toolchain": name,
         },
     )
 

twirl-toolchain/register-toolchains.bzl

@@ -0,0 +1,40 @@
+def _toolchain_configuration_repository_impl(repository_ctx):
+    repository_ctx.file(
+        "BUILD.bazel",
+        """\
+load("@bazel_skylib//rules:common_settings.bzl", "string_setting")
+
+string_setting(
+    name = "twirl-toolchain",
+    build_setting_default = "{}",
+    visibility = ["//visibility:public"],
+)
+
+string_setting(
+    name = "original-twirl-toolchain",
+    build_setting_default = "",
+    visibility = ["//visibility:public"],
+)
+""".format(repository_ctx.attr.default_toolchain_name),
+    )
+
+_toolchain_configuration_repository = repository_rule(
+    attrs = {
+        "default_toolchain_name": attr.string(mandatory = True),
+    },
+    doc = "Defines build settings used by the Twirl toolchains to use. This is done in a separate repository so we can provide the default dynamically.",
+    implementation = _toolchain_configuration_repository_impl,
+)
+
+def twirl_register_toolchains(
+        default_toolchain_name,
+        toolchains = [
+            "//twirl-toolchain:twirl-3",
+            "//twirl-toolchain:twirl-2-13",
+        ]):
+    _toolchain_configuration_repository(
+        name = "rules_twirl_toolchain",
+        default_toolchain_name = default_toolchain_name,
+    )
+
+    native.register_toolchains(*toolchains)

twirl-toolchain/transitions.bzl

@@ -1,8 +1,8 @@
 # This approach of incoming transition, store original values, outgoing
 # transition, reset to original values is inspired by what the rules_go
 # folks are doing.
-toolchain_setting_key = "//twirl-toolchain"
-original_toolchain_setting_key = "//twirl-toolchain:original-twirl-toolchain"
+toolchain_setting_key = "@rules_twirl_toolchain//:twirl-toolchain"
+original_toolchain_setting_key = "@rules_twirl_toolchain//:original-twirl-toolchain"
 
 def _twirl_toolchain_transition_impl(settings, attr):
     """Update the rules_twirl toolchain to the overridden value. Store