[interop][SwiftToCxx] add 'has-expose-attr-or-stdlib' mode to -clang-header-expose-decls flag

This mode allows the user to fallback to the old behavior that required @expose annotations, while still having standard library interfaces emitted in one header

Author: hyp

include/swift/Frontend/FrontendOptions.h

@@ -406,7 +406,10 @@ class FrontendOptions {
     /// Expose all public declarations in the generated header.
     AllPublic,
     /// Expose declarations only when they have expose attribute.
-    HasExposeAttr
+    HasExposeAttr,
+    /// Expose declarations only when they have expose attribute or are the
+    /// implicitly exposed Stdlib declarations.
+    HasExposeAttrOrImplicitDeps
   };
 
   /// Indicates which declarations should be exposed in the generated clang

lib/Frontend/ArgsToFrontendOptionsConverter.cpp

@@ -310,11 +310,18 @@ bool ArgsToFrontendOptionsConverter::convert(
   Opts.UseSharedResourceFolder = !Args.hasArg(OPT_use_static_resource_dir);
   Opts.DisableBuildingInterface = Args.hasArg(OPT_disable_building_interface);
   if (const Arg *A = Args.getLastArg(options::OPT_clang_header_expose_decls)) {
-      Opts.ClangHeaderExposedDecls =
-          llvm::StringSwitch<llvm::Optional<FrontendOptions::ClangHeaderExposeBehavior>>(A->getValue())
-              .Case("all-public", FrontendOptions::ClangHeaderExposeBehavior::AllPublic)
-              .Case("has-expose-attr", FrontendOptions::ClangHeaderExposeBehavior::HasExposeAttr)
-              .Default(llvm::None);
+    Opts.ClangHeaderExposedDecls =
+        llvm::StringSwitch<
+            llvm::Optional<FrontendOptions::ClangHeaderExposeBehavior>>(
+            A->getValue())
+            .Case("all-public",
+                  FrontendOptions::ClangHeaderExposeBehavior::AllPublic)
+            .Case("has-expose-attr",
+                  FrontendOptions::ClangHeaderExposeBehavior::HasExposeAttr)
+            .Case("has-expose-attr-or-stdlib",
+                  FrontendOptions::ClangHeaderExposeBehavior::
+                      HasExposeAttrOrImplicitDeps)
+            .Default(llvm::None);
   }
 
   Opts.StrictImplicitModuleContext = Args.hasArg(OPT_strict_implicit_module_context,

lib/PrintAsClang/PrintAsClang.cpp

@@ -566,11 +566,18 @@ bool swift::printAsClangHeader(raw_ostream &os, ModuleDecl *M,
     bool requiresExplicitExpose =
         !frontendOpts.ClangHeaderExposedDecls.has_value() ||
         *frontendOpts.ClangHeaderExposedDecls ==
-            FrontendOptions::ClangHeaderExposeBehavior::HasExposeAttr;
-    // Default dependency behavior is used when the -clang-header-expose-decls
-    // flag is not specified.
-    bool defaultDependencyBehavior =
-        !frontendOpts.ClangHeaderExposedDecls.has_value();
+            FrontendOptions::ClangHeaderExposeBehavior::HasExposeAttr ||
+        *frontendOpts.ClangHeaderExposedDecls ==
+            FrontendOptions::ClangHeaderExposeBehavior::
+                HasExposeAttrOrImplicitDeps;
+    // Swift stdlib dependencies are emitted into the same header when
+    // -clang-header-expose-decls flag is not specified, or when it allows
+    // implicit dependency emission.
+    bool addStdlibDepsInline =
+        !frontendOpts.ClangHeaderExposedDecls.has_value() ||
+        *frontendOpts.ClangHeaderExposedDecls ==
+            FrontendOptions::ClangHeaderExposeBehavior::
+                HasExposeAttrOrImplicitDeps;
 
     std::string moduleContentsBuf;
     llvm::raw_string_ostream moduleContents{moduleContentsBuf};
@@ -581,7 +588,7 @@ bool swift::printAsClangHeader(raw_ostream &os, ModuleDecl *M,
     writeImports(os, deps.imports, *M, bridgingHeader, frontendOpts,
                  clangHeaderSearchInfo, /*useCxxImport=*/true);
     // Embed the standard library directly.
-    if (defaultDependencyBehavior && deps.dependsOnStandardLibrary) {
+    if (addStdlibDepsInline && deps.dependsOnStandardLibrary) {
       assert(!M->isStdlibModule());
       SwiftToClangInteropContext interopContext(
           *M->getASTContext().getStdlibModule(), irGenOpts);
@@ -592,7 +599,7 @@ bool swift::printAsClangHeader(raw_ostream &os, ModuleDecl *M,
                                interopContext,
                                /*requiresExposedAttribute=*/true);
       os << "#endif // " << macroGuard << "\n";
-      }
+    }
 
       os << moduleContents.str();
   });

test/Interop/SwiftToCxx/expose-attr/expose-swift-decls-to-cxx.swift

@@ -14,6 +14,11 @@
 // RUN: %target-swift-frontend -parse-as-library %t/Expose.swiftinterface -enable-library-evolution -disable-objc-attr-requires-foundation-module -typecheck -module-name Expose -enable-experimental-cxx-interop -clang-header-expose-decls=has-expose-attr -emit-clang-header-path %t/expose.h
 // RUN: %FileCheck %s < %t/expose.h
 
+// RUN: %empty-directory(%t)
+// RUN: %target-swift-frontend %s -enable-library-evolution -typecheck -emit-module-interface-path %t/Expose.swiftinterface -module-name Expose
+// RUN: %target-swift-frontend -parse-as-library %t/Expose.swiftinterface -enable-library-evolution -disable-objc-attr-requires-foundation-module -typecheck -module-name Expose -clang-header-expose-decls=has-expose-attr-or-stdlib -emit-clang-header-path %t/expose.h
+// RUN: %FileCheck %s < %t/expose.h
+
 @_expose(Cxx)
 public func exposed1() {
 }

test/Interop/SwiftToCxx/stdlib/stdlib-dep-inline-in-cxx.swift

@@ -1,10 +1,13 @@
 // RUN: %empty-directory(%t)
 
 // RUN: %target-swift-frontend -typecheck %s -typecheck -module-name UseOptional -enable-experimental-cxx-interop -emit-clang-header-path %t/stdlib.h
-// RUN: %target-swift-frontend -typecheck %s -typecheck -module-name UseOptional2 -enable-experimental-cxx-interop -emit-clang-header-path %t/stdlib2.h
-
 // RUN: %FileCheck %s < %t/stdlib.h
 
+// RUN: %target-swift-frontend -typecheck %s -typecheck -module-name UseOptional -enable-experimental-cxx-interop -clang-header-expose-decls=has-expose-attr-or-stdlib -emit-clang-header-path %t/stdlib_expose_flag.h
+// RUN: %FileCheck %s < %t/stdlib_expose_flag.h
+
+// RUN: %target-swift-frontend -typecheck %s -typecheck -module-name UseOptional2 -enable-experimental-cxx-interop -emit-clang-header-path %t/stdlib2.h
+
 // RUN: cat %t/stdlib.h %t/stdlib2.h > %t/two_includes.h
 
 // RUN: %check-interop-cxx-header-in-clang(-DSWIFT_CXX_INTEROP_HIDE_STL_OVERLAY %t/two_includes.h -Wno-unused-private-field -Wno-unused-function)