Simplify and cleanup how implicit toolchain dependencies are managed.

-   When propagating implicit deps in the toolchain, merge and propagate the providers instead of the `Target` object itself. The `Target` object is fairly heavyweight and not intended to be propagated around the build graph.
-   Remove the `swift.minimal_deps` feature and the distinction between "required" and "optional" implicit deps.

PiperOrigin-RevId: 367044294

swift/internal/compiling.bzl

@@ -42,7 +42,6 @@ load(
     "SWIFT_FEATURE_FASTBUILD",
     "SWIFT_FEATURE_FULL_DEBUG_INFO",
     "SWIFT_FEATURE_INDEX_WHILE_BUILDING",
-    "SWIFT_FEATURE_MINIMAL_DEPS",
     "SWIFT_FEATURE_MODULE_MAP_HOME_IS_CWD",
     "SWIFT_FEATURE_NO_EMBED_DEBUG_MODULE",
     "SWIFT_FEATURE_NO_GENERATED_MODULE_MAP",
@@ -1298,16 +1297,26 @@ def compile(
         *   `swiftmodule`: The `.swiftmodule` file that was produced by the
             compiler.
     """
-    generated_module_deps = (
-        deps + swift_toolchain.generated_header_module_implicit_deps
+
+    # Collect the `SwiftInfo` providers that represent the dependencies of the
+    # Objective-C generated header module -- this includes the dependencies of
+    # the Swift module, plus any additional dependencies that the toolchain says
+    # are required for all generated header modules. These are used immediately
+    # below to write the module map for the header's module (to provide the
+    # `use` declarations), and later in this function when precompiling the
+    # module.
+    generated_module_deps_swift_infos = (
+        get_providers(deps, SwiftInfo) +
+        swift_toolchain.generated_header_module_implicit_deps_providers.swift_infos
     )
+
     compile_outputs, other_outputs = _declare_compile_outputs(
+        srcs = srcs,
         actions = actions,
         feature_configuration = feature_configuration,
         generated_header_name = generated_header_name,
-        generated_module_deps = generated_module_deps,
+        generated_module_deps_swift_infos = generated_module_deps_swift_infos,
         module_name = module_name,
-        srcs = srcs,
         target_name = target_name,
         user_compile_flags = copts,
     )
@@ -1328,11 +1337,9 @@ def compile(
     # into the action prerequisites so that configurators have easy access to
     # the full set of values and inputs through a single accessor.
     merged_providers = _merge_targets_providers(
+        implicit_deps_providers = swift_toolchain.implicit_deps_providers,
         supports_objc_interop = swift_toolchain.supports_objc_interop,
-        targets = deps + private_deps + get_implicit_deps(
-            feature_configuration = feature_configuration,
-            swift_toolchain = swift_toolchain,
-        ),
+        targets = deps + private_deps,
     )
 
     # Flattening this `depset` is necessary because we need to extract the
@@ -1427,11 +1434,7 @@ def compile(
             module_map_file = compile_outputs.generated_module_map_file,
             module_name = module_name,
             swift_info = create_swift_info(
-                swift_infos = [
-                    dep[SwiftInfo]
-                    for dep in generated_module_deps
-                    if SwiftInfo in dep
-                ],
+                swift_infos = generated_module_deps_swift_infos,
             ),
             swift_toolchain = swift_toolchain,
             target_name = target_name,
@@ -1568,32 +1571,12 @@ def precompile_clang_module(
 
     return precompiled_module
 
-def get_implicit_deps(feature_configuration, swift_toolchain):
-    """Gets the list of implicit dependencies from the toolchain.
-
-    Args:
-        feature_configuration: The feature configuration, which determines
-            whether optional implicit dependencies are included.
-        swift_toolchain: The Swift toolchain.
-
-    Returns:
-        A list of targets that should be treated as implicit dependencies of
-        the toolchain under the given feature configuration.
-    """
-    deps = list(swift_toolchain.required_implicit_deps)
-    if not is_feature_enabled(
-        feature_configuration = feature_configuration,
-        feature_name = SWIFT_FEATURE_MINIMAL_DEPS,
-    ):
-        deps.extend(swift_toolchain.optional_implicit_deps)
-    return deps
-
 def _declare_compile_outputs(
         *,
         actions,
         feature_configuration,
         generated_header_name,
-        generated_module_deps,
+        generated_module_deps_swift_infos,
         module_name,
         srcs,
         target_name,
@@ -1606,8 +1589,9 @@ def _declare_compile_outputs(
             `swift_common.configure_features`.
         generated_header_name: The desired name of the generated header for this
             module, or `None` if no header should be generated.
-        generated_module_deps: Dependencies of the module for the generated
-            header of the target being compiled.
+        generated_module_deps_swift_infos: `SwiftInfo` providers from
+            dependencies of the module for the generated header of the target
+            being compiled.
         module_name: The name of the Swift module being compiled.
         srcs: The list of source files that will be compiled.
         target_name: The name (excluding package path) of the target being
@@ -1676,11 +1660,10 @@ def _declare_compile_outputs(
         # Collect the names of Clang modules that the module being built
         # directly depends on.
         dependent_module_names = sets.make()
-        for dep in generated_module_deps:
-            if SwiftInfo in dep:
-                for module in dep[SwiftInfo].direct_modules:
-                    if module.clang:
-                        sets.insert(dependent_module_names, module.name)
+        for swift_info in generated_module_deps_swift_infos:
+            for module in swift_info.direct_modules:
+                if module.clang:
+                    sets.insert(dependent_module_names, module.name)
 
         generated_module_map = derived_files.module_map(
             actions = actions,
@@ -1868,7 +1851,10 @@ def _declare_validated_generated_header(actions, generated_header_name):
 
     return actions.declare_file(generated_header_name)
 
-def _merge_targets_providers(supports_objc_interop, targets):
+def _merge_targets_providers(
+        implicit_deps_providers,
+        supports_objc_interop,
+        targets):
     """Merges the compilation-related providers for the given targets.
 
     This function merges the `CcInfo`, `SwiftInfo`, and `apple_common.Objc`
@@ -1878,6 +1864,8 @@ def _merge_targets_providers(supports_objc_interop, targets):
     their data.
 
     Args:
+        implicit_deps_providers: The implicit deps providers `struct` from the
+            Swift toolchain.
         supports_objc_interop: `True` if the current toolchain supports
             Objective-C interop and the `apple_common.Objc` providers should
             also be used to determine compilation flags and inputs. If `False`,
@@ -1895,9 +1883,9 @@ def _merge_targets_providers(supports_objc_interop, targets):
         *   `objc_info`: The merged `apple_common.Objc` provider of the targets.
         *   `swift_info`: The merged `SwiftInfo` provider of the targets.
     """
-    cc_infos = []
-    objc_infos = []
-    swift_infos = []
+    cc_infos = list(implicit_deps_providers.cc_infos)
+    objc_infos = list(implicit_deps_providers.objc_infos)
+    swift_infos = list(implicit_deps_providers.swift_infos)
 
     # TODO(b/146575101): This is only being used to preserve the current
     # behavior of strict Objective-C include paths being propagated one more
@@ -2018,7 +2006,8 @@ def new_objc_provider(
         module_map,
         static_archives,
         swiftmodules,
-        objc_header = None):
+        objc_header = None,
+        objc_providers = []):
     """Creates an `apple_common.Objc` provider for a Swift target.
 
     Args:
@@ -2038,15 +2027,17 @@ def new_objc_provider(
             `None`, no headers will be propagated. This header is only needed
             for Swift code that defines classes that should be exposed to
             Objective-C.
+        objc_providers: Additional `apple_common.Objc` providers from transitive
+            dependencies not provided by the `deps` argument.
 
     Returns:
         An `apple_common.Objc` provider that should be returned by the calling
         rule.
     """
-    objc_providers = get_providers(deps, apple_common.Objc)
+    all_objc_providers = get_providers(deps, apple_common.Objc) + objc_providers
     objc_provider_args = {
         "link_inputs": depset(direct = swiftmodules + link_inputs),
-        "providers": objc_providers,
+        "providers": all_objc_providers,
         "uses_swift": True,
     }
 
@@ -2086,7 +2077,7 @@ def new_objc_provider(
     # direct deps' Objective-C module maps to dependents, because those Swift
     # modules still need to see them. We need to construct a new transitive objc
     # provider to get the correct strict propagation behavior.
-    transitive_objc_provider_args = {"providers": objc_providers}
+    transitive_objc_provider_args = {"providers": all_objc_providers}
     if module_map:
         transitive_objc_provider_args["module_map"] = depset(
             direct = [module_map],

swift/internal/feature_names.bzl

@@ -88,13 +88,6 @@ SWIFT_FEATURE_FULL_DEBUG_INFO = "swift.full_debug_info"
 # If enabled, the compilation action for a target will produce an index store.
 SWIFT_FEATURE_INDEX_WHILE_BUILDING = "swift.index_while_building"
 
-# If enabled, Swift libraries, binaries, and tests will only have automatic
-# dependencies on the targets provided by the toolchain's
-# `required_implicit_deps` field but not those in the `optional_implicit_deps`
-# field. Users may still explicitly list the latter in the `deps` of their
-# targets if they are needed.
-SWIFT_FEATURE_MINIMAL_DEPS = "swift.minimal_deps"
-
 # If enabled, compilation actions and module map generation will assume that the
 # header paths in module maps are relative to the current working directory
 # (i.e., the workspace root); if disabled, header paths in module maps are

swift/internal/providers.bzl

@@ -73,12 +73,38 @@ Swift toolchain depends on.
         "cpu": """\
 `String`. The CPU architecture that the toolchain is targeting.
 """,
-        "generated_header_module_implicit_deps": """\
-`List` of `Target`s. Targets whose `SwiftInfo` providers should be treated as
-compile-time inputs to actions that precompile the explicit module for the
-generated Objective-C header of a Swift module. This is used to provide modular
-dependencies for the fixed inclusions (Darwin, Foundation) that are
-unconditionally emitted in those files.
+        "generated_header_module_implicit_deps_providers": """\
+A `struct` with the following fields, which are providers from targets that
+should be treated as compile-time inputs to actions that precompile the explicit
+module for the generated Objective-C header of a Swift module:
+
+*   `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.
+
+This is used to provide modular dependencies for the fixed inclusions (Darwin,
+Foundation) that are unconditionally emitted in those files.
+
+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.
+""",
+        "implicit_deps_providers": """\
+A `struct` with the following fields, which represent providers from targets
+that should be added as implicit dependencies of any Swift compilation or
+linking target (but not to 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.
 """,
         "linker_opts_producer": """\
 Skylib `partial`. A partial function that returns the flags that should be
@@ -96,11 +122,6 @@ The partial should be called with two arguments:
         "object_format": """\
 `String`. The object file format of the platform that the toolchain is
 targeting. The currently supported values are `"elf"` and `"macho"`.
-""",
-        "optional_implicit_deps": """\
-`List` of `Target`s. Library targets that should be added as implicit
-dependencies of any `swift_library`, `swift_binary`, or `swift_test` target that
-does not have the feature `swift.minimal_deps` applied.
 """,
         "requested_features": """\
 `List` of `string`s. Features that should be implicitly enabled by default for
@@ -111,11 +132,6 @@ their negation in the `features` attribute of a target/package or in the
 These features determine various compilation and debugging behaviors of the
 Swift build rules, and they are also passed to the C++ APIs used when linking
 (so features defined in CROSSTOOL may be used here).
-""",
-        "required_implicit_deps": """\
-`List` of `Target`s. Library targets that should be unconditionally added as
-implicit dependencies of any `swift_library`, `swift_binary`, or `swift_test`
-target.
 """,
         "root_dir": """\
 `String`. The workspace-relative root directory of the toolchain.
@@ -283,6 +299,7 @@ def create_swift_module(
 
 def create_swift_info(
         *,
+        direct_swift_infos = [],
         modules = [],
         swift_infos = []):
     """Creates a new `SwiftInfo` provider with the given values.
@@ -293,25 +310,38 @@ def create_swift_info(
     are set consistently.
 
     This function can also be used to do a simple merge of `SwiftInfo`
-    providers, by leaving all of the arguments except for `swift_infos` as their
-    empty defaults. In that case, the returned provider will not represent a
-    true Swift module; it is merely a "collector" for other dependencies.
+    providers, by leaving the `modules` argument unspecified. In that case, the
+    returned provider will not represent a true Swift module; it is merely a
+    "collector" for other dependencies.
 
     Args:
+        direct_swift_infos: A list of `SwiftInfo` providers from dependencies
+            whose direct modules should be treated as direct modules in the
+            resulting provider, in addition to their transitive modules being
+            merged.
         modules: A list of values (as returned by `swift_common.create_module`)
             that represent Clang and/or Swift module artifacts that are direct
             outputs of the target being built.
-        swift_infos: A list of `SwiftInfo` providers from dependencies, whose
-            transitive fields should be merged into the new one. If omitted, no
-            transitive data is collected.
+        swift_infos: A list of `SwiftInfo` providers from dependencies whose
+            transitive modules should be merged into the resulting provider.
 
     Returns:
         A new `SwiftInfo` provider with the given values.
     """
 
-    transitive_modules = [x.transitive_modules for x in swift_infos]
+    direct_modules = modules + [
+        provider.modules
+        for provider in direct_swift_infos
+    ]
+    transitive_modules = [
+        provider.transitive_modules
+        for provider in direct_swift_infos + swift_infos
+    ]
 
     return SwiftInfo(
-        direct_modules = modules,
-        transitive_modules = depset(modules, transitive = transitive_modules),
+        direct_modules = direct_modules,
+        transitive_modules = depset(
+            direct_modules,
+            transitive = transitive_modules,
+        ),
     )

swift/internal/swift_binary_test.bzl

@@ -217,13 +217,10 @@ def _swift_linking_rule_impl(
     )
     user_link_flags.extend(toolchain_linker_flags)
 
-    # Collect the dependencies of the target being linked as well as the
-    # toolchain's implicit dependencies (depending on the current feature
-    # configuration).
-    deps_to_link = ctx.attr.deps + swift_common.get_implicit_deps(
-        feature_configuration = feature_configuration,
-        swift_toolchain = swift_toolchain,
-    )
+    # Collect linking contexts from any of the toolchain's implicit
+    # dependencies.
+    for cc_info in swift_toolchain.implicit_deps_providers.cc_infos:
+        additional_linking_contexts.append(cc_info.linking_context)
 
     # If a custom malloc implementation has been provided, pass that to the
     # linker as well.
@@ -244,7 +241,7 @@ def _swift_linking_rule_impl(
         additional_inputs = additional_inputs_to_linker,
         additional_linking_contexts = additional_linking_contexts,
         cc_feature_configuration = cc_feature_configuration,
-        deps = deps_to_link,
+        deps = ctx.attr.deps,
         grep_includes = ctx.file._grep_includes,
         name = ctx.label.name,
         objects = objects_to_link,

swift/internal/swift_common.bzl

@@ -33,7 +33,6 @@ load(
     ":compiling.bzl",
     "compile",
     "derive_module_name",
-    "get_implicit_deps",
     "precompile_clang_module",
 )
 load(
@@ -64,7 +63,6 @@ swift_common = struct(
     create_swift_info = create_swift_info,
     create_swift_module = create_swift_module,
     derive_module_name = derive_module_name,
-    get_implicit_deps = get_implicit_deps,
     is_enabled = is_feature_enabled,
     library_rule_attrs = swift_library_rule_attrs,
     precompile_clang_module = precompile_clang_module,