Support implicit C/Objective-C dependencies that are passed when compiling any explicit Clang module.

The toolchain's `clang_implicit_deps` are not passed to Swift compilations;
only to actions that compile an explicit C/Objective-C module using
`swift_common.precompile_clang_module`.

PiperOrigin-RevId: 375816204

Author: allevato

swift/internal/compiling.bzl

@@ -1526,9 +1526,7 @@ def compile(
             is_swift_generated_header = True,
             module_map_file = compile_outputs.generated_module_map_file,
             module_name = module_name,
-            swift_info = create_swift_info(
-                swift_infos = generated_module_deps_swift_infos,
-            ),
+            swift_infos = generated_module_deps_swift_infos,
             swift_toolchain = swift_toolchain,
             target_name = target_name,
         )
@@ -1574,7 +1572,7 @@ def precompile_clang_module(
         target_name,
         bin_dir = None,
         genfiles_dir = None,
-        swift_info = None):
+        swift_infos = []):
     """Precompiles an explicit Clang module that is compatible with Swift.
 
     Args:
@@ -1607,8 +1605,8 @@ def precompile_clang_module(
             path is added to ClangImporter's header search paths for
             compatibility with Bazel's C++ and Objective-C rules which support
             inclusions of generated headers from that location.
-        swift_info: A `SwiftInfo` provider that contains dependencies required
-            to compile this module.
+        swift_infos: A list of `SwiftInfo` providers representing dependencies
+            required to compile this module.
 
     Returns:
         A `File` representing the precompiled module (`.pcm`) file, or `None` if
@@ -1623,7 +1621,7 @@ def precompile_clang_module(
         is_swift_generated_header = False,
         module_map_file = module_map_file,
         module_name = module_name,
-        swift_info = swift_info,
+        swift_infos = swift_infos,
         swift_toolchain = swift_toolchain,
         target_name = target_name,
     )
@@ -1640,7 +1638,7 @@ def _precompile_clang_module(
         target_name,
         bin_dir = None,
         genfiles_dir = None,
-        swift_info = None):
+        swift_infos = []):
     """Precompiles an explicit Clang module that is compatible with Swift.
 
     Args:
@@ -1675,8 +1673,8 @@ def _precompile_clang_module(
             path is added to ClangImporter's header search paths for
             compatibility with Bazel's C++ and Objective-C rules which support
             inclusions of generated headers from that location.
-        swift_info: A `SwiftInfo` provider that contains dependencies required
-            to compile this module.
+        swift_infos: A list of `SwiftInfo` providers representing dependencies
+            required to compile this module.
 
     Returns:
         A `File` representing the precompiled module (`.pcm`) file, or `None` if
@@ -1702,8 +1700,20 @@ def _precompile_clang_module(
         target_name = target_name,
     )
 
-    if swift_info:
-        transitive_modules = swift_info.transitive_modules.to_list()
+    if not is_swift_generated_header:
+        implicit_swift_infos = (
+            swift_toolchain.clang_implicit_deps_providers.swift_infos
+        )
+    else:
+        implicit_swift_infos = []
+
+    if not is_swift_generated_header and implicit_swift_infos:
+        swift_infos = list(swift_infos)
+        swift_infos.extend(implicit_swift_infos)
+
+    if swift_infos:
+        merged_swift_info = create_swift_info(swift_infos = swift_infos)
+        transitive_modules = merged_swift_info.transitive_modules.to_list()
     else:
         transitive_modules = []
 

swift/internal/providers.bzl

@@ -110,6 +110,21 @@ using this toolchain.
         "cc_toolchain_info": """\
 The `cc_common.CcToolchainInfo` provider from the Bazel C++ toolchain that this
 Swift toolchain depends on.
+""",
+        "clang_implicit_deps_providers": """\
+A `struct` with the following fields, which represent providers from targets
+that should be added as implicit dependencies of any precompiled explicit
+C/Objective-C modules:
+
+*   `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.
+
+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.
 """,
         "cpu": """\
 `String`. The CPU architecture that the toolchain is targeting.

swift/internal/swift_clang_module_aspect.bzl

@@ -423,15 +423,14 @@ def _handle_module(
     """
     attr = aspect_ctx.rule.attr
 
-    if swift_infos:
-        merged_swift_info = create_swift_info(swift_infos = swift_infos)
-    else:
-        merged_swift_info = None
+    all_swift_infos = (
+        swift_infos + swift_toolchain.clang_implicit_deps_providers.swift_infos
+    )
 
     # Collect the names of Clang modules that the module being built directly
     # depends on.
     dependent_module_names = []
-    for swift_info in swift_infos:
+    for swift_info in all_swift_infos:
         for module in swift_info.direct_modules:
             if module.clang:
                 dependent_module_names.append(module.name)
@@ -450,8 +449,8 @@ def _handle_module(
         )
 
     if not module_map_file:
-        if merged_swift_info:
-            return [merged_swift_info]
+        if all_swift_infos:
+            return [create_swift_info(swift_infos = swift_infos)]
         else:
             return []
 
@@ -474,7 +473,7 @@ def _handle_module(
             genfiles_dir = aspect_ctx.genfiles_dir,
             module_map_file = module_map_file,
             module_name = module_name,
-            swift_info = merged_swift_info,
+            swift_infos = swift_infos,
             swift_toolchain = swift_toolchain,
             target_name = target.label.name,
         )

swift/internal/swift_toolchain.bzl

@@ -212,6 +212,9 @@ def _swift_toolchain_impl(ctx):
             action_configs = all_action_configs,
             all_files = depset(all_files),
             cc_toolchain_info = cc_toolchain,
+            clang_implicit_deps_providers = (
+                collect_implicit_deps_providers([])
+            ),
             cpu = ctx.attr.arch,
             feature_allowlists = [
                 target[SwiftFeatureAllowlistInfo]

swift/internal/xcode_swift_toolchain.bzl

@@ -730,6 +730,9 @@ def _xcode_swift_toolchain_impl(ctx):
             action_configs = all_action_configs,
             all_files = depset(all_files),
             cc_toolchain_info = cc_toolchain,
+            clang_implicit_deps_providers = collect_implicit_deps_providers(
+                ctx.attr.clang_implicit_deps,
+            ),
             cpu = cpu,
             feature_allowlists = [
                 target[SwiftFeatureAllowlistInfo]
@@ -764,6 +767,22 @@ xcode_swift_toolchain = rule(
     attrs = dicts.add(
         swift_toolchain_driver_attrs(),
         {
+            "clang_implicit_deps": attr.label_list(
+                doc = """\
+A list of labels to library targets that should be unconditionally added as
+implicit dependencies of any explicit C/Objective-C module compiled by the Swift
+toolchain.
+
+Despite being C/Objective-C modules, the targets specified by this attribute
+must propagate the `SwiftInfo` provider because the Swift build rules use that
+provider to look up Clang module requirements. In particular, the targets must
+propagate the provider in their rule implementation themselves and not rely on
+the implicit traversal performed by `swift_clang_module_aspect`; the latter is
+not possible as it would create a dependency cycle between the toolchain and the
+implicit dependencies.
+""",
+                providers = [[SwiftInfo]],
+            ),
             "feature_allowlists": attr.label_list(
                 doc = """\
 A list of `swift_feature_allowlist` targets that allow or prohibit packages from