Incorporate improvements from #1428

Incorporates key improvements from PR #1428 into the system library
implementation to create a more robust and complete solution:

- Add linker settings support to Swift targets via `linkopts`
- Add standard C/Objc compilation flags
- Support both explicit headers from `clang_src_info` and glob patterns
- Handle modulemap files when provided, otherwise auto-generate
- Add comprehensive unit tests for system library targets

The enhanced implementation now supports both system libraries with
explicit modulemaps (like in #1428) and those without
(like `GRDBSQLite`).

Author: jpsim

swiftpkg/internal/swiftpkg_build_files.bzl

@@ -24,7 +24,7 @@ def _new_for_target(repository_ctx, pkg_ctx, target, artifact_infos = []):
     if target.module_type == module_types.clang:
         return _clang_target_build_file(repository_ctx, pkg_ctx, target)
     elif target.module_type == module_types.swift:
-        return _swift_target_build_file(pkg_ctx, target)
+        return _swift_target_build_file(repository_ctx, pkg_ctx, target)
     elif target.module_type == module_types.system_library:
         return _system_library_build_file(target)
     elif target.module_type == module_types.binary:
@@ -41,7 +41,7 @@ def _new_for_target(repository_ctx, pkg_ctx, target, artifact_infos = []):
 
 # MARK: - Swift Target
 
-def _swift_target_build_file(pkg_ctx, target):
+def _swift_target_build_file(repository_ctx, pkg_ctx, target):
     if target.swift_src_info == None:
         fail("Expected a `swift_src_info`. name: ", target.name)
 
@@ -188,6 +188,15 @@ def _swift_target_build_file(pkg_ctx, target):
     if len(copts) > 0:
         attrs["copts"] = bzl_selects.to_starlark(copts, mutually_inclusive = True)
 
+    linkopts = []
+    if target.linker_settings != None:
+        linkopts.extend(lists.flatten([
+            bzl_selects.new_from_build_setting(bs)
+            for bs in target.linker_settings.linked_libraries
+        ]))
+    if linkopts:
+        attrs["linkopts"] = _starlarkify_clang_attrs(repository_ctx, {"linkopts": linkopts})["linkopts"]
+
     if target.resources:
         swift_apple_res_bundle_info = _apple_resource_bundle_for_swift(
             pkg_ctx,
@@ -710,47 +719,52 @@ def _starlarkify_clang_attrs(repository_ctx, attrs):
 # MARK: - System Library Targets
 
 def _system_library_build_file(target):
-    # System libraries are typically C/Objc libraries that need to be exposed to Swift.
-    # We generate a cc_library with a swift_interop_hint for proper Swift interop.
-
     bzl_target_name = target.label.name
 
-    # Build the cc_library attributes
-    attrs = {}
+    attrs = {
+        "visibility": ["//visibility:public"],
+    }
+
+    # Standard C/Objc compilation flags from SPM
+    copts = [
+        "-fblocks",
+        "-fobjc-arc",
+        "-fPIC",
+        "-DSWIFT_PACKAGE=1",
+    ]
+    attrs["copts"] = copts
 
-    # For system libraries, sources is always empty. We need to use glob to find files.
-    # Look for all .h files in the target path
-    hdrs_glob = paths.join(target.path, "**/*.h")
+    # Determine headers: prefer explicit headers from clang_src_info, fallback to glob
+    if target.clang_src_info and target.clang_src_info.hdrs:
+        attrs["hdrs"] = target.clang_src_info.hdrs
+    else:
+        hdrs_glob = paths.join(target.path, "**/*.h")
+        attrs["hdrs"] = scg.new_fn_call("glob", [hdrs_glob])
 
-    # System libraries typically have headers and a module.modulemap
-    # We'll use glob patterns to find them
-    attrs["hdrs"] = scg.new_fn_call("glob", [hdrs_glob])
+    # Determine module map: use explicit if provided, otherwise let rules_swift auto-generate
+    module_map_file = None
+    if target.clang_src_info and target.clang_src_info.modulemap_path:
+        module_map_file = target.clang_src_info.modulemap_path
 
-    # Create swift_interop_hint for C/Swift interop
+    # Create swift_interop_hint for Swift interop
     aspect_hint_target_name = pkginfo_targets.swift_hint_label_name(bzl_target_name)
 
     load_stmts = [swift_interop_hint_load_stmt]
     decls = []
 
-    # Create the swift_interop_hint
     decls.append(
         build_decls.new(
             kind = swift_kinds.interop_hint,
             name = aspect_hint_target_name,
             attrs = {
-                # For system libraries, we often don't have a module map file
-                # Set to None and let rules_swift generate one if needed
-                "module_map": None,
+                "module_map": module_map_file,
                 "module_name": target.c99name,
             },
         ),
     )
 
-    # Add aspect_hints to cc_library
     attrs["aspect_hints"] = [":{}".format(aspect_hint_target_name)]
-    attrs["visibility"] = ["//visibility:public"]
 
-    # Create the cc_library
     decls.append(
         build_decls.new(
             kind = clang_kinds.library,

swiftpkg/tests/swiftpkg_build_files_tests.bzl

@@ -84,6 +84,15 @@ def _pkg_info(
                 type = pkginfos.new_product_type(executable = True),
                 targets = ["SwiftExecutableTarget"],
             ),
+            pkginfos.new_product(
+                name = "SystemLibraryTarget",
+                type = pkginfos.new_product_type(
+                    library = pkginfos.new_library_type(
+                        library_type_kinds.automatic,
+                    ),
+                ),
+                targets = ["SystemLibraryTarget"],
+            ),
         ],
         targets = [
             # Old-style regular library that is used to create a binary from an
@@ -508,6 +517,20 @@ def _pkg_info(
                     ],
                 ),
             ),
+            pkginfos.new_target(
+                name = "SystemLibraryTarget",
+                type = "system",
+                c99name = "SystemLibraryTarget",
+                module_type = "SystemLibraryTarget",
+                path = "Sources/SystemLibraryTarget",
+                sources = [],
+                dependencies = [],
+                repo_name = _repo_name,
+                clang_src_info = pkginfos.new_clang_src_info(
+                    hdrs = ["someHeader.h"],
+                    modulemap_path = "module.modulemap",
+                ),
+            ),
         ],
         expose_build_targets = expose_build_targets,
     )
@@ -1161,6 +1184,33 @@ swift_interop_hint(
     module_map = "ObjcLibraryWithResources.rspm_modulemap",
     module_name = "ObjcLibraryWithResources",
 )
+""",
+        ),
+        struct(
+            msg = "System library target",
+            name = "SystemLibraryTarget",
+            pkg_info = _pkg_info(),
+            exp = """\
+load("@build_bazel_rules_swift//swift:swift.bzl", "swift_interop_hint")
+
+swift_interop_hint(
+    name = "SystemLibraryTarget.rspm_swift_hint",
+    module_map = "module.modulemap",
+    module_name = "SystemLibraryTarget",
+)
+
+cc_library(
+    name = "SystemLibraryTarget.rspm",
+    aspect_hints = [":SystemLibraryTarget.rspm_swift_hint"],
+    copts = [
+        "-fblocks",
+        "-fobjc-arc",
+        "-fPIC",
+        "-DSWIFT_PACKAGE=1",
+    ],
+    hdrs = ["someHeader.h"],
+    visibility = ["//visibility:public"],
+)
 """,
         ),
         struct(