Add Scalafmt deps toolchain (bazel-contrib#1107)

Author: liucijus

scala/scalafmt/BUILD

@@ -1,4 +1,6 @@
 load("//scala:scala.bzl", "scala_binary")
+load("//scala/scalafmt/toolchain:toolchain.bzl", "export_scalafmt_deps", "scalafmt_toolchain")
+load("@io_bazel_rules_scala//scala:providers.bzl", "declare_deps_provider")
 
 filegroup(
     name = "runner",
@@ -18,10 +20,8 @@ scala_binary(
     main_class = "io.bazel.rules_scala.scalafmt.ScalafmtWorker",
     visibility = ["//visibility:public"],
     deps = [
+        ":scalafmt_classpath",
         "//src/java/io/bazel/rulesscala/worker",
-        "@com_geirsson_metaconfig_core",
-        "@org_scalameta_parsers",
-        "@org_scalameta_scalafmt_core",
     ],
 )
 
@@ -34,3 +34,35 @@ scalafmt_singleton(
     name = "phase_scalafmt",
     visibility = ["//visibility:public"],
 )
+
+declare_deps_provider(
+    name = "scalafmt_classpath_provider",
+    deps_id = "scalafmt_classpath",
+    visibility = ["//visibility:public"],
+    deps = [
+        "@com_geirsson_metaconfig_core",
+        "@org_scalameta_parsers",
+        "@org_scalameta_scalafmt_core",
+    ],
+)
+
+scalafmt_toolchain(
+    name = "scalafmt_toolchain_impl",
+    dep_providers = [
+        ":scalafmt_classpath_provider",
+    ],
+    visibility = ["//visibility:public"],
+)
+
+toolchain(
+    name = "scalafmt_toolchain",
+    toolchain = ":scalafmt_toolchain_impl",
+    toolchain_type = "//scala/scalafmt/toolchain:scalafmt_toolchain_type",
+    visibility = ["//visibility:public"],
+)
+
+export_scalafmt_deps(
+    name = "scalafmt_classpath",
+    deps_id = "scalafmt_classpath",
+    visibility = ["//visibility:public"],
+)

scala/scalafmt/scalafmt_repositories.bzl

@@ -498,3 +498,5 @@ def scalafmt_repositories(
         ],
         server_urls = maven_servers,
     )
+
+    native.register_toolchains("@io_bazel_rules_scala//scala/scalafmt:scalafmt_toolchain")

scala/scalafmt/toolchain/BUILD

@@ -0,0 +1,4 @@
+toolchain_type(
+    name = "scalafmt_toolchain_type",
+    visibility = ["//visibility:public"],
+)

scala/scalafmt/toolchain/toolchain.bzl

@@ -0,0 +1,36 @@
+load("@io_bazel_rules_scala//scala:providers.bzl", _DepsInfo = "DepsInfo")
+load("//scala/private/toolchain_deps:toolchain_deps.bzl", "expose_toolchain_deps")
+
+def _scalafmt_toolchain_impl(ctx):
+    toolchain = platform_common.ToolchainInfo(
+        dep_providers = ctx.attr.dep_providers,
+    )
+    return [toolchain]
+
+scalafmt_toolchain = rule(
+    _scalafmt_toolchain_impl,
+    attrs = {
+        "dep_providers": attr.label_list(
+            default = [
+                "@io_bazel_rules_scala//scala/scalafmt:scalafmt_classpath_provider",
+            ],
+            providers = [_DepsInfo],
+        ),
+    },
+)
+
+def _export_scalafmt_deps_impl(ctx):
+    return expose_toolchain_deps(
+        ctx,
+        "@io_bazel_rules_scala//scala/scalafmt/toolchain:scalafmt_toolchain_type",
+    )
+
+export_scalafmt_deps = rule(
+    _export_scalafmt_deps_impl,
+    attrs = {
+        "deps_id": attr.string(
+            mandatory = True,
+        ),
+    },
+    toolchains = ["@io_bazel_rules_scala//scala/scalafmt/toolchain:scalafmt_toolchain_type"],
+)