add support to SPM SystemLibrary

swiftpkg/internal/pkginfos.bzl

@@ -375,6 +375,18 @@ def _new_target_from_json_maps(
                 pkg_path = pkg_path,
                 sources = clang_src_info.explicit_srcs + clang_src_info.hdrs,
             )
+    elif module_type == module_types.system_library:
+        clang_src_info = _new_clang_src_info_from_sources(
+            repository_ctx = repository_ctx,
+            pkg_path = pkg_path,
+            c99name = c99name,
+            target_path = target_path,
+            source_paths = source_paths,
+            public_hdrs_path = public_hdrs_path,
+            exclude_paths = exclude_paths,
+            other_hdr_srch_paths = [],
+        )
+
 
     return _new_target(
         name = target_name,

swiftpkg/internal/swiftpkg_build_files.bzl

@@ -641,8 +641,48 @@ def _starlarkify_clang_attrs(repository_ctx, attrs):
 
 # buildifier: disable=unused-variable
 def _system_library_build_file(target):
-    # GH009(chuck): Implement _system_library_build_file
-    return None
+    attrs = {
+        "visibility": ["//:__subpackages__"],
+    }
+
+    # These flags are used by SPM when compiling clang modules.
+    copts = [
+        # Enable 'blocks' language feature
+        "-fblocks",
+        # Synthesize retain and release calls for Objective-C pointers
+        "-fobjc-arc",
+        # Enable support for PIC macros
+        "-fPIC",
+        # The SWIFT_PACKAGE define is a magical value that SPM uses when it
+        # builds clang libraries that will be used as Swift modules.
+        "-DSWIFT_PACKAGE=1",
+    ]
+    attrs["copts"] = copts
+
+    module_map_file = target.clang_src_info.modulemap_path
+    attrs["module_map"] = module_map_file
+
+    # System library targets must include a modulemap file.
+    # https://github.com/swiftlang/swift-package-manager/blob/12c14222fdde2ffd8303a2c805fed1b1eb802e5c/Sources/PackageLoading/PackageBuilder.swift#L853
+    if not module_map_file:
+        fail("Expected a modulemap file for a system library target. name: ", target.name)
+
+    header_files = target.clang_src_info.hdrs
+    attrs["hdrs"] = header_files
+
+    bzl_target_name = pkginfo_targets.bazel_label_name(target)
+
+    decls = [ 
+        build_decls.new(
+            kind = objc_kinds.library,
+            name = bzl_target_name,
+            attrs = attrs,
+        )
+    ]
+
+    return build_files.new(
+        decls = decls,
+    )
 
 # MARK: - Apple xcframework Targets