Adds the repository rule xcode_sdk_frameworks

It scans and configures all SDK frameworks which are required for explicit module builds.

Specifically, it 1) uses the bazel_tools//tools/osx:xcode_configure.bzl to fetch all local Xcode infos, and
  2) finds all frameworks under the xcode SDK path,
  3) uses the swiftc -scan-dependencies mode to fetch the dependency graph among all Swift and Clang SDK modules.

We use swift_module_alias to represent a Swift SDK module and sdk_clang_module for a Clang SDK module.

Next steps:
 The dependency among swift_module_alias and sdk_clang_module doesn't work yet. We need to fix that.

.bazelrc

@@ -65,6 +65,7 @@ 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
+build:explicit_modules --repo_env=EXPLICIT_MODULES=1
 
 # By default don't upload local results to remote cache, only CI does this.
 build --noremote_upload_local_results

MODULE.bazel

@@ -101,3 +101,12 @@ use_repo(
  apple_non_module_deps,
  "xctestrunner",
 )
+
+# Load xcode_sdk_frameworks
+xcode_sdk_frameworks = use_repo_rule(
+ "//rules:xcode_sdk_frameworks.bzl",
+ "xcode_sdk_frameworks",
+)
+xcode_sdk_frameworks(
+ name = "xcode_sdk_frameworks",
+)

rules/explicit_module/sdk_clang_module.bzl

@@ -1,4 +1,5 @@
 load("@build_bazel_rules_swift//swift/internal:feature_names.bzl", "SWIFT_FEATURE_SYSTEM_MODULE")
+load("@build_bazel_rules_swift//swift/internal:providers.bzl", "create_swift_info")
 load("@build_bazel_rules_swift//swift/internal:swift_common.bzl", "swift_common")
 
 def _sdk_clang_module_impl(ctx):
@@ -11,10 +12,16 @@ def _sdk_clang_module_impl(ctx):
  # 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()),
+ # Required to add sdk_clang_module targets to the deps of swift_module_alias.
+ # TODO(cshi): create the SwiftInfo correctly
+ create_swift_info(),
  ]
 
 sdk_clang_module = rule(
  attrs = {
+ "deps": attr.label_list(
+ doc = "The deps of the SDK clang module",
+ ),
  "module_map": attr.string(
  doc = """\
 The path to a SDK framework module map.