Add feature to propagate the generated module map

Allows `objc_library` to modularly import `swift_library` targets without having to generate a similar module map.

examples/apple/objc_interop_modulemap/BUILD

@@ -0,0 +1,40 @@
+# This example tests that Swift code can be called from Objective-C code and
+# vice versa when it is linked into the existing native linking rules for Apple
+# platforms.
+
+load(
+    "//swift:swift.bzl",
+    "swift_binary",
+    "swift_library",
+)
+
+licenses(["notice"])
+
+objc_library(
+    name = "PrintStream",
+    srcs = ["OIPrintStream.m"],
+    hdrs = ["OIPrintStream.h"],
+    target_compatible_with = ["@platforms//os:macos"],
+)
+
+swift_library(
+    name = "Printer",
+    srcs = ["Printer.swift"],
+    # features = ["swift.propagate_generated_module_map"],
+    generated_header_name = "generated_header/Printer-Swift.h",
+    generates_header = True,
+    deps = [":PrintStream"],
+)
+
+objc_library(
+    name = "main",
+    srcs = ["main.m"],
+    enable_modules = True,
+    target_compatible_with = ["@platforms//os:macos"],
+    deps = [":Printer"],
+)
+
+swift_binary(
+    name = "objc_interop_modulemap",
+    deps = [":main"],
+)

examples/apple/objc_interop_modulemap/OIPrintStream.h

@@ -0,0 +1,24 @@
+// Copyright 2018 The Bazel Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#import <Foundation/Foundation.h>
+
+/** A very contrived interface for writing strings to a file handle. */
+@interface OIPrintStream : NSObject
+
+- (nonnull instancetype)initWithFileHandle:(nonnull NSFileHandle *)fileHandle;
+
+- (void)printString:(nonnull NSString *)message;
+
+@end

examples/apple/objc_interop_modulemap/OIPrintStream.m

@@ -0,0 +1,35 @@
+// Copyright 2018 The Bazel Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#import "examples/apple/objc_interop_modulemap/OIPrintStream.h"
+
+@implementation OIPrintStream {
+  NSFileHandle *_fileHandle;
+}
+
+- (instancetype)initWithFileHandle:(nonnull NSFileHandle *)fileHandle {
+  if (self = [super init]) {
+    _fileHandle = fileHandle;
+  }
+  return self;
+}
+
+- (void)printString:(nonnull NSString *)message {
+  NSData *data = [message dataUsingEncoding:NSUTF8StringEncoding];
+  [_fileHandle writeData:data];
+  NSData *newline = [NSData dataWithBytes:"\n" length:1];
+  [_fileHandle writeData:newline];
+}
+
+@end

examples/apple/objc_interop_modulemap/Printer.swift

@@ -0,0 +1,32 @@
+// Copyright 2018 The Bazel Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+import Foundation
+import examples_apple_objc_interop_modulemap_PrintStream
+
+@objc(OIPrinter)
+public class Printer: NSObject {
+
+  private let stream: OIPrintStream
+  private let prefix: String
+
+  @objc public init(prefix: NSString) {
+    self.stream = OIPrintStream(fileHandle: .standardOutput)
+    self.prefix = prefix as String
+  }
+
+  @objc public func print(_ message: NSString) {
+    stream.print("\(prefix)\(message)")
+  }
+}

examples/apple/objc_interop_modulemap/main.m

@@ -0,0 +1,23 @@
+// Copyright 2018 The Bazel Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+@import examples_apple_objc_interop_modulemap_Printer;
+
+int main(int argc, char **argv) {
+  @autoreleasepool {
+    OIPrinter *printer = [[OIPrinter alloc] initWithPrefix:@"*** "];
+    [printer print:@"Hello world"];
+  }
+  return 0;
+}

swift/internal/compiling.bzl

@@ -68,6 +68,7 @@ load(
     "SWIFT_FEATURE_OPT",
     "SWIFT_FEATURE_OPT_USES_OSIZE",
     "SWIFT_FEATURE_OPT_USES_WMO",
+    "SWIFT_FEATURE_PROPAGATE_GENERATED_MODULE_MAP",
     "SWIFT_FEATURE_REWRITE_GENERATED_HEADER",
     "SWIFT_FEATURE_SPLIT_DERIVED_FILES_GENERATION",
     "SWIFT_FEATURE_SUPPORTS_BARE_SLASH_REGEX",
@@ -2642,6 +2643,17 @@ to use swift_common.compile(include_dev_srch_paths = ...) instead.\
         transitive_modules = transitive_modules,
     )
 
+    includes = []
+    public_hdrs = []
+    if compile_outputs.generated_header_file:
+        public_hdrs = [compile_outputs.generated_header_file]
+        if compile_outputs.generated_module_map_file and is_feature_enabled(
+            feature_configuration = feature_configuration,
+            feature_name = SWIFT_FEATURE_PROPAGATE_GENERATED_MODULE_MAP,
+        ):
+            public_hdrs.append(compile_outputs.generated_module_map_file)
+            includes = [compile_outputs.generated_module_map_file.dirname]
+
     module_context = create_module(
         name = module_name,
         clang = create_clang_module(
@@ -2650,7 +2662,8 @@ to use swift_common.compile(include_dev_srch_paths = ...) instead.\
                 defines = defines,
                 deps = deps,
                 feature_configuration = feature_configuration,
-                public_hdrs = compact([compile_outputs.generated_header_file]),
+                includes = includes,
+                public_hdrs = public_hdrs,
                 swift_toolchain = swift_toolchain,
                 target_name = target_name,
             ),
@@ -2859,6 +2872,7 @@ def _create_cc_compilation_context(
         defines,
         deps,
         feature_configuration,
+        includes,
         public_hdrs,
         swift_toolchain,
         target_name):
@@ -2878,6 +2892,8 @@ def _create_cc_compilation_context(
             `SwiftInfo`, or `apple_common.Objc`.
         feature_configuration: A feature configuration obtained from
             `swift_common.configure_features`.
+        includes: Include paths that should be propagated by the new compilation
+            context.
         public_hdrs: Public headers that should be propagated by the new
             compilation context (for example, the module's generated header).
         swift_toolchain: The `SwiftToolchainInfo` provider of the toolchain.
@@ -2912,6 +2928,7 @@ def _create_cc_compilation_context(
                 feature_configuration = feature_configuration,
             ),
             name = target_name,
+            includes = includes,
             public_hdrs = public_hdrs,
         )
         return compilation_context

swift/internal/derived_files.bzl

@@ -153,7 +153,12 @@ def _module_map(actions, target_name):
     Returns:
         The declared `File`.
     """
-    return actions.declare_file("{}.swift.modulemap".format(target_name))
+
+    # Path is two directories deep to avoid automatic discovery by
+    # `-fimplicit-module-maps` and with non-related include paths
+    return actions.declare_file(
+        "{}_modulemap/_/module.modulemap".format(target_name),
+    )
 
 def _modulewrap_object(actions, target_name):
     """Declares the object file used to wrap Swift modules for ELF binaries.

swift/internal/feature_names.bzl

@@ -142,6 +142,11 @@ SWIFT_FEATURE_NO_ASAN_VERSION_CHECK = "swift.no_asan_version_check"
 # the target is not generating a header.
 SWIFT_FEATURE_NO_GENERATED_MODULE_MAP = "swift.no_generated_module_map"
 
+# If enabled, the generates module map is named `module.modulemap` and
+# the parent directory is added as to `CcInfo.compliation_context.includes`.
+# This allows `objc_library` to import the Swift module.
+SWIFT_FEATURE_PROPAGATE_GENERATED_MODULE_MAP = "swift.propagate_generated_module_map"
+
 # If enabled, builds using the "opt" compilation mode will invoke `swiftc` with
 # the `-whole-module-optimization` flag (in addition to `-O`).
 SWIFT_FEATURE_OPT_USES_WMO = "swift.opt_uses_wmo"

test/private_deps_tests.bzl

@@ -94,8 +94,8 @@ def private_deps_test_suite(name):
     private_deps_provider_test(
         name = "{}_client_cc_deps_modulemaps".format(name),
         expected_files = [
-            "/test/fixtures/private_deps/public_cc.swift.modulemap",
-            "-/test/fixtures/private_deps/private_cc.swift.modulemap",
+            "/test/fixtures/private_deps/public_cc_modulemap/_/module.modulemap",
+            "-/test/fixtures/private_deps/private_cc_modulemap_/module.modulemap",
         ],
         field = "transitive_modules.clang!.module_map!",
         provider = "SwiftInfo",