Add the module_mapping flag to the Swift rules

doc/providers.md

@@ -87,7 +87,7 @@ SwiftToolchainInfo(<a href="#SwiftToolchainInfo-action_configs">action_configs</
                    <a href="#SwiftToolchainInfo-const_protocols_to_gather">const_protocols_to_gather</a>, <a href="#SwiftToolchainInfo-debug_outputs_provider">debug_outputs_provider</a>, <a href="#SwiftToolchainInfo-developer_dirs">developer_dirs</a>,
                    <a href="#SwiftToolchainInfo-entry_point_linkopts_provider">entry_point_linkopts_provider</a>, <a href="#SwiftToolchainInfo-feature_allowlists">feature_allowlists</a>,
                    <a href="#SwiftToolchainInfo-generated_header_module_implicit_deps_providers">generated_header_module_implicit_deps_providers</a>, <a href="#SwiftToolchainInfo-implicit_deps_providers">implicit_deps_providers</a>,
-                   <a href="#SwiftToolchainInfo-package_configurations">package_configurations</a>, <a href="#SwiftToolchainInfo-requested_features">requested_features</a>, <a href="#SwiftToolchainInfo-root_dir">root_dir</a>, <a href="#SwiftToolchainInfo-swift_worker">swift_worker</a>,
+                   <a href="#SwiftToolchainInfo-module_aliases">module_aliases</a>, <a href="#SwiftToolchainInfo-package_configurations">package_configurations</a>, <a href="#SwiftToolchainInfo-requested_features">requested_features</a>, <a href="#SwiftToolchainInfo-root_dir">root_dir</a>, <a href="#SwiftToolchainInfo-swift_worker">swift_worker</a>,
                    <a href="#SwiftToolchainInfo-test_configuration">test_configuration</a>, <a href="#SwiftToolchainInfo-tool_configs">tool_configs</a>, <a href="#SwiftToolchainInfo-unsupported_features">unsupported_features</a>)
 </pre>
 
@@ -109,6 +109,7 @@ that use the toolchain.
 | <a id="SwiftToolchainInfo-feature_allowlists"></a>feature_allowlists |  A list of `SwiftFeatureAllowlistInfo` providers that allow or prohibit packages from requesting or disabling features.    |
 | <a id="SwiftToolchainInfo-generated_header_module_implicit_deps_providers"></a>generated_header_module_implicit_deps_providers |  A `struct` with the following fields, which are providers from targets that should be treated as compile-time inputs to actions that precompile the explicit module for the generated Objective-C header of a Swift module:<br><br>*   `cc_infos`: A list of `CcInfo` providers from targets specified as the     toolchain's implicit dependencies. *   `objc_infos`: A list of `apple_common.Objc` providers from targets specified     as the toolchain's implicit dependencies. *   `swift_infos`: A list of `SwiftInfo` providers from targets specified as the     toolchain's implicit dependencies.<br><br>This is used to provide modular dependencies for the fixed inclusions (Darwin, Foundation) that are unconditionally emitted in those files.<br><br>For ease of use, this field is never `None`; it will always be a valid `struct` containing the fields described above, even if those lists are empty.    |
 | <a id="SwiftToolchainInfo-implicit_deps_providers"></a>implicit_deps_providers |  A `struct` with the following fields, which represent providers from targets that should be added as implicit dependencies of any Swift compilation or linking target (but not to precompiled explicit C/Objective-C modules):<br><br>*   `cc_infos`: A list of `CcInfo` providers from targets specified as the     toolchain's implicit dependencies. *   `objc_infos`: A list of `apple_common.Objc` providers from targets specified     as the toolchain's implicit dependencies. *   `swift_infos`: A list of `SwiftInfo` providers from targets specified as the     toolchain's implicit dependencies.<br><br>For ease of use, this field is never `None`; it will always be a valid `struct` containing the fields described above, even if those lists are empty.    |
+| <a id="SwiftToolchainInfo-module_aliases"></a>module_aliases |  A `SwiftModuleAliasesInfo` provider that defines the module aliases to use during compilation.    |
 | <a id="SwiftToolchainInfo-package_configurations"></a>package_configurations |  A list of `SwiftPackageConfigurationInfo` providers that specify additional compilation configuration options that are applied to targets on a per-package basis.    |
 | <a id="SwiftToolchainInfo-requested_features"></a>requested_features |  `List` of `string`s. Features that should be implicitly enabled by default for targets built using this toolchain, unless overridden by the user by listing their negation in the `features` attribute of a target/package or in the `--features` command line flag.<br><br>These features determine various compilation and debugging behaviors of the Swift build rules, and they are also passed to the C++ APIs used when linking (so features defined in CROSSTOOL may be used here).    |
 | <a id="SwiftToolchainInfo-root_dir"></a>root_dir |  `String`. The workspace-relative root directory of the toolchain.    |

swift/BUILD

@@ -6,6 +6,7 @@ load(
     "repeatable_string_flag",
 )
 load(":swift_interop_hint.bzl", "swift_interop_hint")
+load(":swift_module_mapping.bzl", "swift_module_mapping")
 
 package(default_visibility = ["//visibility:public"])
 
@@ -368,3 +369,17 @@ filegroup(
     name = "empty",
     visibility = ["//visibility:private"],
 )
+
+# Provides the mapping that will be passed to the compiler as module aliases.
+label_flag(
+    name = "module_mapping",
+    build_setting_default = ":empty_module_mapping",
+)
+
+# The default empty module mapping used when the `:module_mapping` flag is not
+# set.
+swift_module_mapping(
+    name = "empty_module_mapping",
+    aliases = {},
+    visibility = ["//visibility:private"],
+)

swift/providers.bzl

@@ -286,6 +286,10 @@ linking target (but not to precompiled explicit C/Objective-C modules):
 
 For ease of use, this field is never `None`; it will always be a valid `struct`
 containing the fields described above, even if those lists are empty.
+""",
+        "module_aliases": """\
+A `SwiftModuleAliasesInfo` provider that defines the module aliases to use
+during compilation.
 """,
         "package_configurations": """\
 A list of `SwiftPackageConfigurationInfo` providers that specify additional

swift/swift_module_mapping.bzl

@@ -29,7 +29,7 @@ def _swift_module_mapping_impl(ctx):
 
     aliases = ctx.attr.aliases
     new_names_seen = dict()
-    for original_name, new_name in aliases:
+    for original_name, new_name in aliases.items():
         previous_new_name = new_names_seen.get(new_name, None)
         if previous_new_name:
             fail((

swift/toolchains/BUILD

@@ -14,6 +14,7 @@ bzl_library(
         "//swift/internal:debugging",
         "//swift/internal:feature_names",
         "//swift/internal:features",
+        "//swift/internal:providers",
         "//swift/internal:target_triples",
         "//swift/internal:utils",
         "//swift/internal:wmo",
@@ -39,6 +40,7 @@ bzl_library(
         "//swift/internal:attrs",
         "//swift/internal:feature_names",
         "//swift/internal:features",
+        "//swift/internal:providers",
         "//swift/internal:target_triples",
         "//swift/internal:utils",
         "//swift/internal:wmo",

swift/toolchains/swift_toolchain.bzl

@@ -63,6 +63,7 @@ load(
     "SWIFT_FEATURE_USE_MODULE_WRAP",
 )
 load("//swift/internal:features.bzl", "features_for_build_modes")
+load("//swift/internal:providers.bzl", "SwiftModuleAliasesInfo")
 load("//swift/internal:target_triples.bzl", "target_triples")
 load(
     "//swift/internal:utils.bzl",
@@ -529,6 +530,7 @@ def _swift_toolchain_impl(ctx):
         generated_header_module_implicit_deps_providers = (
             collect_implicit_deps_providers([])
         ),
+        module_aliases = ctx.attr._module_mapping[SwiftModuleAliasesInfo].aliases,
         implicit_deps_providers = collect_implicit_deps_providers(
             [],
             additional_cc_infos = [swift_linkopts_cc_info],
@@ -626,6 +628,12 @@ The label of the `string_list` containing additional flags that should be passed
 to the compiler for exec transition builds.
 """,
             ),
+            "_module_mapping": attr.label(
+                default = Label(
+                    "@build_bazel_rules_swift//swift:module_mapping",
+                ),
+                providers = [[SwiftModuleAliasesInfo]],
+            ),
             "_worker": attr.label(
                 cfg = "exec",
                 allow_files = True,

swift/toolchains/xcode_swift_toolchain.bzl

@@ -67,6 +67,7 @@ load(
     "SWIFT_FEATURE__FORCE_ALWAYSLINK_TRUE",
 )
 load("//swift/internal:features.bzl", "features_for_build_modes")
+load("//swift/internal:providers.bzl", "SwiftModuleAliasesInfo")
 load("//swift/internal:target_triples.bzl", "target_triples")
 load(
     "//swift/internal:utils.bzl",
@@ -785,6 +786,13 @@ def _xcode_swift_toolchain_impl(ctx):
             ),
         )
 
+    module_aliases = ctx.attr._module_mapping[SwiftModuleAliasesInfo].aliases
+    if module_aliases and not _is_xcode_at_least_version(xcode_config, "14.0"):
+        fail(
+            "Module mappings are only supported by Swift 5.7 (Xcode 14.0) " +
+            "and higher.",
+        )
+
     swift_toolchain_info = SwiftToolchainInfo(
         action_configs = all_action_configs,
         cc_toolchain_info = cc_toolchain,
@@ -812,6 +820,7 @@ def _xcode_swift_toolchain_impl(ctx):
             additional_cc_infos = [swift_linkopts_providers.cc_info],
             additional_objc_infos = [swift_linkopts_providers.objc_info],
         ),
+        module_aliases = module_aliases,
         package_configurations = [
             target[SwiftPackageConfigurationInfo]
             for target in ctx.attr.package_configurations
@@ -936,6 +945,12 @@ The label of the `string_list` containing additional flags that should be passed
 to the compiler for exec transition builds.
 """,
             ),
+            "_module_mapping": attr.label(
+                default = Label(
+                    "@build_bazel_rules_swift//swift:module_mapping",
+                ),
+                providers = [[SwiftModuleAliasesInfo]],
+            ),
             "_worker": attr.label(
                 cfg = "exec",
                 allow_files = True,