Adds sdk_clang_module to represent sdk clang modules in explicit module builds

Also add a basic example for explicit module builds. Run 'bazel build --config=explicit_modules //example/explicit_module:hello_world'.

Author: congt

.bazelrc

@@ -62,6 +62,10 @@ build:remote_cache --noslim_profile
 build:remote_cache --remote_cache=grpcs://remote.buildbuddy.io
 build:remote_cache --remote_timeout=3600
 
+# Configure for explicit module compilation
+build:explicit_modules --features=swift.use_c_modules
+build:explicit_modules --features=swift.emit_c_module
+
 # By default don't upload local results to remote cache, only CI does this.
 build --noremote_upload_local_results
 build:ci --remote_upload_local_results

example/explicit_module/BUILD.bazel

@@ -0,0 +1,23 @@
+load("@build_bazel_rules_swift//swift:swift.bzl", "swift_binary")
+load("//rules/explicit_module:sdk_clang_module.bzl", "sdk_clang_module")
+
+sdk_clang_module(
+    name = "swift_concurrency_shims",
+    module_map = "__BAZEL_XCODE_SDKROOT__/usr/lib/swift/shims/module.modulemap",
+    module_name = "_SwiftConcurrencyShims",
+)
+
+sdk_clang_module(
+    name = "shims",
+    module_map = "__BAZEL_XCODE_SDKROOT__/usr/lib/swift/shims/module.modulemap",
+    module_name = "SwiftShims",
+)
+
+swift_binary(
+    name = "hello_world",
+    srcs = ["main.swift"],
+    deps = [
+        ":shims",
+        ":swift_concurrency_shims",
+    ],
+)

example/explicit_module/main.swift

@@ -0,0 +1 @@
+print("Hello world")

rules/explicit_module/BUILD.bazel

@@ -0,0 +1,40 @@
+load("@build_bazel_rules_swift//swift/internal:feature_names.bzl", "SWIFT_FEATURE_SYSTEM_MODULE")
+load("@build_bazel_rules_swift//swift/internal:swift_common.bzl", "swift_common")
+
+def _sdk_clang_module_impl(ctx):
+    return [
+        swift_common.create_swift_interop_info(
+            module_map = ctx.attr.module_map,
+            module_name = ctx.attr.module_name,
+            requested_features = [SWIFT_FEATURE_SYSTEM_MODULE],
+        ),
+        # We need to return CcInfo and its compilation_context. We may also consider to update swift_clang_module_aspect.
+        # See https://github.com/bazelbuild/rules_swift/blob/d68b21471e4e9d922b75e2b0621082b8ce017d11/swift/internal/swift_clang_module_aspect.bzl#L548
+        CcInfo(compilation_context = cc_common.create_compilation_context()),
+    ]
+
+sdk_clang_module = rule(
+    attrs = {
+        "module_map": attr.string(
+            doc = """\
+The path to a SDK framework module map.
+Variables `__BAZEL_XCODE_SDKROOT__` and `__BAZEL_XCODE_DEVELOPER_DIR__` will be substitued
+appropriately for, i.e.  
+`/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk`
+and
+`/Applications/Xcode.app/Contents/Developer` respectively.
+""",
+            mandatory = True,
+        ),
+        "module_name": attr.string(
+            doc = """\
+The name of the top-level module in the module map that this target represents.
+""",
+            mandatory = True,
+        ),
+    },
+    doc = """\
+A rule representing a SDK clang module. It's required for explicit module builds.
+""",
+    implementation = _sdk_clang_module_impl,
+)

rules/explicit_module/sdk_clang_module.bzl

@@ -85,8 +85,8 @@ def _rules_ios_bzlmod_dependencies():
     _maybe(
         http_archive,
         name = "build_bazel_rules_swift",
-        sha256 = "bb01097c7c7a1407f8ad49a1a0b1960655cf823c26ad2782d0b7d15b323838e2",
-        url = "https://github.com/bazelbuild/rules_swift/releases/download/1.18.0/rules_swift.1.18.0.tar.gz",
+        sha256 = "a91877169614a1fd24afc7e2a7c5e77f8e05caa8332dde115ba4ca4a5b6d14ec",
+        url = "https://github.com/bazelbuild/rules_swift/archive/8c144a2c28af3af7b78b5fd679550e6783a19194.zip",
     )
 
     _maybe(