Merge pull request swiftlang#75269 from swiftlang/gaborh/forward-declare-classes

[cxx-interop] Forward declare classes

Author: Xazax-hun

lib/PrintAsClang/DeclAndTypePrinter.cpp

@@ -325,8 +325,6 @@ class DeclAndTypePrinter::Implementation
 
     if (outputLang == OutputLanguageMode::Cxx) {
       // FIXME: Non objc class.
-      // FIXME: forward decl should be handled by ModuleWriter.
-      ClangValueTypePrinter::forwardDeclType(os, CD, owningPrinter);
       ClangClassTypePrinter(os).printClassTypeDecl(
           CD, [&]() { printMembers(CD->getMembers()); }, owningPrinter);
       recordEmittedDeclInCurrentCxxLexicalScope(CD);

lib/PrintAsClang/DeclAndTypePrinter.h

@@ -15,6 +15,7 @@
 
 #include "OutputLanguageMode.h"
 
+#include "swift/AST/Decl.h"
 #include "swift/AST/Type.h"
 // for OptionalTypeKind
 #include "swift/ClangImporter/ClangImporter.h"

lib/PrintAsClang/ModuleContentsWriter.cpp

@@ -117,11 +117,7 @@ class ReferencedTypeFinder : public TypeDeclFinder {
 };
 
 class ModuleWriter {
-  enum class EmissionState {
-    NotYetDefined = 0,
-    DefinitionRequested,
-    Defined
-  };
+  enum class EmissionState { NotYetDefined = 0, DefinitionRequested, Defined };
 
   raw_ostream &os;
   SmallPtrSetImpl<ImportModuleTy> &imports;
@@ -309,7 +305,7 @@ class ModuleWriter {
 
   void forwardDeclareType(const TypeDecl *TD) {
     if (outputLangMode == OutputLanguageMode::Cxx) {
-      if (isa<StructDecl>(TD) || isa<EnumDecl>(TD)) {
+      if (isa<StructDecl>(TD) || isa<EnumDecl>(TD) || isa<ClassDecl>(TD)) {
         auto *NTD = cast<NominalTypeDecl>(TD);
         if (!addImport(NTD))
           forwardDeclareCxxValueTypeIfNeeded(NTD);
@@ -474,7 +470,12 @@ class ModuleWriter {
       return false;
 
     (void)forwardDeclareMemberTypes(CD->getMembers(), CD);
-    seenTypes[CD] = { EmissionState::Defined, true };
+    auto [it, inserted] =
+        seenTypes.try_emplace(CD, EmissionState::NotYetDefined, false);
+    if (outputLangMode == OutputLanguageMode::Cxx &&
+        (inserted || !it->second.second))
+      ClangValueTypePrinter::forwardDeclType(os, CD, printer);
+    it->second = {EmissionState::Defined, true};
     os << '\n';
     printer.print(CD);
     return true;

lib/PrintAsClang/PrintClangValueType.h

@@ -41,7 +41,6 @@ class ClangValueTypePrinter {
   /// corresponds to the given structure or enum declaration.
   void printValueTypeDecl(const NominalTypeDecl *typeDecl,
                           llvm::function_ref<void(void)> bodyPrinter,
-
                           DeclAndTypePrinter &declAndTypePrinter);
 
   /// Print the use of a C++ struct/enum parameter value as it's passed to the

test/Interop/SwiftToCxx/class/swift-class-ordering.swift

@@ -0,0 +1,11 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-swift-frontend %s -typecheck -module-name Class -clang-header-expose-decls=all-public -emit-clang-header-path %t/class.h
+
+// RUN: %check-interop-cxx-header-in-clang(%t/class.h)
+
+public class SwiftNode {
+}
+
+public struct SwiftLinkedList {
+  public var head: SwiftNode
+}