Simplify swift_common.compile so that it returns a SwiftInfo that…

… can be propagated by callers.

The impetus for this change was the fact that inferred cross-import overlay providers weren't being merged into the propagated `SwiftInfo`, so compiling a target that directly depended on one would succeed but compiling something depending on that other target would fail.

Since provider merging was being done by the rules, not by the `compile` call that collected the providers, we would have had to offer a separate API for rule implementations to collect those same cross-import providers or have `compile` return them in some separate fashion.

However, all current callers of `swift_common.compile` are doing exactly the same thing: creating a new `SwiftInfo` that merges the returned module context with the deps `SwiftInfo`s that it already collected and passed to `compile`. So, it's straightforward to just return that `SwiftInfo`, into which we can merge the cross-import providers. This ensures we don't drop anything on the floor *and* it's a major API improvement.

PiperOrigin-RevId: 500710468

swift/internal/compiling.bzl

@@ -256,6 +256,14 @@ def compile(
     Returns:
         A `struct` with the following fields:
 
+        *   `swift_info`: A `SwiftInfo` provider whose list of direct modules
+            contains the single Swift module context produced by this function
+            (identical to the `module_context` field below) and whose transitive
+            modules represent the transitive non-private dependencies. Rule
+            implementations that call this function can typically return this
+            provider directly, except in rare cases like making multiple calls
+            to `swift_common.compile` that need to be merged.
+
         *   `module_context`: A Swift module context (as returned by
             `create_swift_module_context`) that contains the Swift (and
             potentially C/Objective-C) compilation prerequisites of the compiled
@@ -326,14 +334,23 @@ def compile(
         ],
     )
 
+    # These are the `SwiftInfo` providers that will be merged with the compiled
+    # module context and returned as the `swift_info` field of this function's
+    # result. Note that private deps are explicitly not included here, as they
+    # are not supposed to be propagated.
+    #
+    # TODO(allevato): It would potentially clean things up if we included the
+    # toolchain's implicit dependencies here as well. Do this and make sure it
+    # doesn't break anything unexpected.
+    swift_infos_to_propagate = swift_infos + _cross_imported_swift_infos(
+        swift_toolchain = swift_toolchain,
+        user_swift_infos = swift_infos + private_swift_infos,
+    )
+
     all_swift_infos = (
-        swift_infos +
+        swift_infos_to_propagate +
         private_swift_infos +
-        swift_toolchain.implicit_deps_providers.swift_infos +
-        _cross_imported_swift_infos(
-            swift_toolchain = swift_toolchain,
-            user_swift_infos = swift_infos + private_swift_infos,
-        )
+        swift_toolchain.implicit_deps_providers.swift_infos
     )
     merged_swift_info = SwiftInfo(swift_infos = all_swift_infos)
 
@@ -509,6 +526,10 @@ def compile(
         supplemental_outputs = struct(
             indexstore_directory = compile_outputs.indexstore_directory,
         ),
+        swift_info = SwiftInfo(
+            modules = [module_context],
+            swift_infos = swift_infos_to_propagate,
+        ),
     )
 
 def precompile_clang_module(

swift/internal/swift_protoc_gen_aspect.bzl

@@ -487,10 +487,7 @@ def _swift_protoc_gen_aspect_impl(target, aspect_ctx):
             SwiftProtoCompilationInfo(
                 cc_info = cc_info,
                 objc_info = objc_info,
-                swift_info = SwiftInfo(
-                    modules = [module_context],
-                    swift_infos = transitive_swift_infos,
-                ),
+                swift_info = compile_result.swift_info,
             ),
         ]
     else:

swift/swift_grpc_library.bzl

@@ -351,10 +351,7 @@ def _swift_grpc_library_impl(ctx):
             linking_context = linking_context,
         ),
         deps[0][SwiftProtoInfo],
-        SwiftInfo(
-            modules = [module_context],
-            swift_infos = compile_deps_swift_infos,
-        ),
+        compile_result.swift_info,
         OutputGroupInfo(**output_groups),
     ]
 

swift/swift_library.bzl

@@ -258,12 +258,7 @@ def _swift_library_impl(ctx):
             extensions = ["swift"],
             source_attributes = ["srcs"],
         ),
-        SwiftInfo(
-            modules = [module_context],
-            # Note that private_deps are explicitly omitted here; they should
-            # not propagate.
-            swift_infos = swift_infos,
-        ),
+        compile_result.swift_info,
         OutputGroupInfo(**output_groups),
     ]
 

swift/swift_module_alias.bzl

@@ -136,10 +136,7 @@ def _swift_module_alias_impl(ctx):
             compilation_context = module_context.clang.compilation_context,
             linking_context = linking_context,
         ),
-        SwiftInfo(
-            modules = [module_context],
-            swift_infos = swift_infos,
-        ),
+        compile_result.swift_info,
         OutputGroupInfo(**output_groups),
     ]
 

swift/swift_test.bzl

@@ -342,10 +342,7 @@ def _swift_test_impl(ctx):
                 supplemental_outputs.indexstore_directory,
             ])
 
-        swift_infos_including_owner = [SwiftInfo(
-            modules = [compile_result.module_context],
-            swift_infos = swift_infos,
-        )]
+        swift_infos_including_owner = [compile_result.swift_info]
 
         # If we're going to do test discovery below, extract the symbol graph of
         # the module that we just compiled so that we can discover any tests in