Upstream: Add swift_common.is_action_enabled as a public API.

doc/api.md

@@ -463,6 +463,36 @@ A `SwiftToolchainInfo` provider, or `None` if the toolchain was not
   found and not required.
 
 
+<a id="swift_common.is_action_enabled"></a>
+
+## swift_common.is_action_enabled
+
+<pre>
+swift_common.is_action_enabled(<a href="#swift_common.is_action_enabled-action_name">action_name</a>, <a href="#swift_common.is_action_enabled-swift_toolchain">swift_toolchain</a>)
+</pre>
+
+Returns True if the given action is enabled in the Swift toolchain.
+
+This function should be used before invoking APIs that invoke actions that
+might not be available depending on the version of the Swift toolchain. For
+example, `SwiftSynthesizeInterface` actions (created by calling
+`swift_common.synthesize_interface`) are only available starting from Swift
+6.1.
+
+
+**PARAMETERS**
+
+
+| Name  | Description | Default Value |
+| :------------- | :------------- | :------------- |
+| <a id="swift_common.is_action_enabled-action_name"></a>action_name |  The name of the action, which corresponds to the action's mnemonic (for example, `SwiftSynthesizeInterface`).   |  none |
+| <a id="swift_common.is_action_enabled-swift_toolchain"></a>swift_toolchain |  The Swift toolchain being used to build.   |  none |
+
+**RETURNS**
+
+True if the action is enabled, or False if it is not.
+
+
 <a id="swift_common.is_enabled"></a>
 
 ## swift_common.is_enabled

swift/BUILD

@@ -94,6 +94,7 @@ bzl_library(
     name = "swift_common",
     srcs = ["swift_common.bzl"],
     deps = [
+        "//swift/internal:actions",
         "//swift/internal:compiling",
         "//swift/internal:features",
         "//swift/internal:interface_synthesizing",

swift/internal/actions.bzl

@@ -116,8 +116,15 @@ def _apply_action_configs(
 def is_action_enabled(action_name, swift_toolchain):
     """Returns True if the given action is enabled in the Swift toolchain.
 
+    This function should be used before invoking APIs that invoke actions that
+    might not be available depending on the version of the Swift toolchain. For
+    example, `SwiftSynthesizeInterface` actions (created by calling
+    `swift_common.synthesize_interface`) are only available starting from Swift
+    6.1.
+
     Args:
-        action_name: The name of the action.
+        action_name: The name of the action, which corresponds to the action's
+            mnemonic (for example, `SwiftSynthesizeInterface`).
         swift_toolchain: The Swift toolchain being used to build.
 
     Returns:

swift/internal/toolchain_utils.bzl

@@ -51,7 +51,7 @@ def get_swift_toolchain(
         if group and toolchain_type in group.toolchains:
             return group.toolchains[toolchain_type].swift_toolchain
 
-    if toolchain_type in ctx.toolchains:
+    if toolchain_type in ctx.toolchains and ctx.toolchains[toolchain_type]:
         return ctx.toolchains[toolchain_type].swift_toolchain
 
     # TODO(b/205018581): Delete this code path when migration to the new

swift/providers.bzl

@@ -83,6 +83,18 @@ def _swift_info_init(
         direct_swift_infos = [],
         modules = [],
         swift_infos = []):
+    """Creates a `SwiftInfo` provider from the given arguments.
+
+    Args:
+        direct_swift_infos: A list of `SwiftInfo` providers from dependencies
+            whose direct modules should be treated as direct modules in the resulting
+            provider, in addition to their transitive modules being merged.
+        modules: A list of values (as returned by `create_swift_module_context()`)
+            that represent Clang and/or Swift module artifacts that are direct outputs
+            of the target being built.
+        swift_infos: A list of `SwiftInfo` providers from dependencies whose
+            transitive modules should be merged into the resulting provider.
+    """
     direct_modules = modules + [
         module
         for provider in direct_swift_infos

swift/swift_common.bzl

@@ -20,6 +20,10 @@ example, `swift_proto_library` generates Swift source code from `.proto` files
 and then needs to compile them. This module provides that lower-level interface.
 """
 
+load(
+    "//swift/internal:actions.bzl",
+    "is_action_enabled",
+)
 load(
     "//swift/internal:compiling.bzl",
     "compile",
@@ -62,6 +66,7 @@ swift_common = struct(
     create_linking_context_from_compilation_outputs = create_linking_context_from_compilation_outputs,
     extract_symbol_graph = extract_symbol_graph,
     get_toolchain = get_swift_toolchain,
+    is_action_enabled = is_action_enabled,
     is_enabled = is_feature_enabled,
     precompile_clang_module = precompile_clang_module,
     synthesize_interface = synthesize_interface,