Switch the Swift rules over to toolchains

.bazelci/presubmit.yml

@@ -10,13 +10,15 @@ x_defaults:
     test_targets:
       - "//examples/..."
       - "//test/..."
-  linux_common: &linux_common
+  linux_environment: &linux_environment
     platform: ubuntu2004
     environment:
       CC: clang
       SWIFT_VERSION: "5.9.2"
       SWIFT_HOME: "$HOME/swift-$SWIFT_VERSION"
       PATH: "$PATH:$SWIFT_HOME/usr/bin"
+  linux_common: &linux_common
+    <<: *linux_environment
     build_flags: &linux_flags
       # On Linux, we look for Swift toolchain binaries on the path. We may be
       # able to change this when we start auto-downloading toolchains (see
@@ -129,7 +131,11 @@ tasks:
   doc_tests:
     name: "Doc tests"
     bazel: last_green
-    platform: ubuntu2004
+    <<: *linux_environment
+    shell_commands:
+      - "echo --- Downloading and extracting Swift $SWIFT_VERSION to $SWIFT_HOME"
+      - "mkdir $SWIFT_HOME"
+      - "curl https://download.swift.org/swift-${SWIFT_VERSION}-release/ubuntu2004/swift-${SWIFT_VERSION}-RELEASE/swift-${SWIFT_VERSION}-RELEASE-ubuntu20.04.tar.gz | tar xvz --strip-components=1 -C $SWIFT_HOME"
     test_targets:
     - "doc/..."
 

MODULE.bazel

@@ -38,6 +38,8 @@ use_repo(
 apple_cc_configure = use_extension("@build_bazel_apple_support//crosstool:setup.bzl", "apple_cc_configure_extension")
 use_repo(apple_cc_configure, "local_config_apple_cc")
 
+register_toolchains("@build_bazel_rules_swift_local_config//:all")
+
 # Dev dependencies
 bazel_dep(name = "bazel_skylib_gazelle_plugin", version = "1.5.0", dev_dependency = True)
 bazel_dep(name = "gazelle", version = "0.33.0", dev_dependency = True, repo_name = "bazel_gazelle")

swift/internal/toolchain_utils.bzl

@@ -68,8 +68,4 @@ def use_swift_toolchain():
         A list of toolchain types that should be passed to `rule()`, `aspect()`,
         or `exec_group`.
     """
-
-    # TODO(b/205018581): Intentionally empty for now so that rule definitions
-    # can reference the function while still being a no-op. A future change will
-    # add the toolchain type to this list to enable toolchain resolution.
-    return []
+    return [SWIFT_TOOLCHAIN_TYPE]

swift/repositories.bzl

@@ -31,6 +31,7 @@ def _maybe(repo_rule, name, **kwargs):
     if not native.existing_rule(name):
         repo_rule(name = name, **kwargs)
 
+# buildifier: disable=unnamed-macro
 def swift_rules_dependencies(include_bzlmod_ready_dependencies = True):
     """Fetches repositories that are dependencies of `rules_swift`.
 
@@ -213,3 +214,9 @@ def swift_rules_dependencies(include_bzlmod_ready_dependencies = True):
         swift_autoconfiguration,
         name = "build_bazel_rules_swift_local_config",
     )
+
+    if include_bzlmod_ready_dependencies:
+        native.register_toolchains(
+            # Use register_toolchain's target pattern expansion to register all toolchains in the package.
+            "@build_bazel_rules_swift_local_config//:all",
+        )