Merge pull request #65680 from hyp/eng/cxx-warning-nomore-in-stdlib-from-gen-hdr

[interop][SwiftToCxx] avoid importing C++ stdlib in C++ section of ge…

Author: hyp

lib/PrintAsClang/PrintAsClang.cpp

@@ -542,14 +542,19 @@ static void writePostImportPrologue(raw_ostream &os, ModuleDecl &M) {
         "#endif\n\n";
 }
 
+static void writeObjCEpilogue(raw_ostream &os) {
+  // Pop out of `external_source_symbol` attribute
+  // before emitting the C++ section as the C++ section
+  // might include other files in it.
+  os << "#if __has_attribute(external_source_symbol)\n"
+        "# pragma clang attribute pop\n"
+        "#endif\n";
+}
+
 static void writeEpilogue(raw_ostream &os) {
-  os <<
-      "#if __has_attribute(external_source_symbol)\n"
-      "# pragma clang attribute pop\n"
-      "#endif\n"
-      "#pragma clang diagnostic pop\n"
-      // For the macro guard against recursive definition
-      "#endif\n";
+  os << "#pragma clang diagnostic pop\n"
+        // For the macro guard against recursive definition
+        "#endif\n";
 }
 
 static std::string computeMacroGuard(const ModuleDecl *M) {
@@ -577,6 +582,7 @@ bool swift::printAsClangHeader(raw_ostream &os, ModuleDecl *M,
   });
   writePostImportPrologue(os, *M);
   emitObjCConditional(os, [&] { os << objcModuleContents.str(); });
+  writeObjCEpilogue(os);
   emitCxxConditional(os, [&] {
     // FIXME: Expose Swift with @expose by default.
     bool enableCxx = frontendOpts.ClangHeaderExposedDecls.has_value() ||

test/Interop/SwiftToCxx/stdlib/stdlib-in-cxx-no-diagnostics-generated-header.cpp

@@ -0,0 +1,28 @@
+// RUN: %empty-directory(%t)
+// RUN: split-file %s %t
+// RUN: %target-swift-frontend -typecheck %t/print-string.swift -typecheck -module-name Stringer -enable-experimental-cxx-interop -emit-clang-header-path %t/Stringer.h
+
+// Ensure: we don't hit any spurios warnings instantiating
+// C++ standard library templates because of the generated header.
+
+// RUN: %target-interop-build-clangxx -std=gnu++20 -fsyntax-only -c %t/test-stdlib.cpp -I %t -Wall -Werror -Werror=ignored-attributes -Wno-error=unused-command-line-argument
+
+//--- print-string.swift
+
+public func printString(_ s: String) {
+}
+
+//--- test-stdlib.cpp
+
+#include "Stringer.h"
+#include <iostream>
+
+int main() {
+  // Ensure that template instantiations inside C++
+  // standard library in this call don't cause any new diagnostics
+  // because of the generated header.
+  std::cout << "test invoke std::cout\n" << std::endl;
+
+  auto _ = swift::String::init();
+  return 0;
+}

test/PrintAsCxx/empty.swift

@@ -92,6 +92,9 @@
 
 // CHECK-LABEL: #if defined(__OBJC__)
 // CHECK-NEXT:  #endif
+// CHECK-NEXT:  #if __has_attribute(external_source_symbol)
+// CHECK-NEXT:  # pragma clang attribute pop
+// CHECK-NEXT:  #endif
 // CHECK-NEXT:  #if defined(__cplusplus)
 // CHECK-NEXT:  #pragma clang diagnostic push
 // CHECK-NEXT:  #pragma clang diagnostic ignored "-Wnon-modular-include-in-framework-module"

test/PrintAsObjC/Inputs/comments-expected-output.h

@@ -442,11 +442,11 @@ SWIFT_CLASS("_TtC8comments13UnorderedList")
 - (void)f0;
 @end
 
-#endif
-#if defined(__cplusplus)
 #endif
 #if __has_attribute(external_source_symbol)
 # pragma clang attribute pop
 #endif
+#if defined(__cplusplus)
+#endif
 #pragma clang diagnostic pop
 #endif