From d4869193c8de21a896f6b91fbd3d3796222f22cd Mon Sep 17 00:00:00 2001
From: Slava Pestov <spestov@apple.com>
Date: Sat, 1 Nov 2025 22:31:15 -0400
Subject: [PATCH] IRGen: Only skip round-trip demangler check for types that
 involve C++ types

Previously this was disabled entirely if C++ interop was
enabled, which is too broad.
---
 lib/AST/Module.cpp           | 13 ++++++++++-
 lib/IRGen/IRGenDebugInfo.cpp | 45 ++++++++++++++++++++++++++++++++----
 2 files changed, 52 insertions(+), 6 deletions(-)

diff --git a/lib/AST/Module.cpp b/lib/AST/Module.cpp
index c1ee8ae8f5eed..2473495be2cfc 100644
--- a/lib/AST/Module.cpp
+++ b/lib/AST/Module.cpp
@@ -1011,7 +1011,18 @@ void ModuleDecl::lookupMember(SmallVectorImpl<ValueDecl*> &results,
   } else if (privateDiscriminator.empty()) {
     auto newEnd = std::remove_if(results.begin()+oldSize, results.end(),
                                  [](const ValueDecl *VD) -> bool {
-      return VD->getFormalAccess() <= AccessLevel::FilePrivate;
+      // FIXME: The ClangImporter sometimes generates private declarations but
+      // doesn't give their file unit a private discriminator so they mangle
+      // incorrectly.
+      //
+      // The hasClangNode() carveout makes the ASTDemangler work properly in
+      // this case.
+      //
+      // We should fix things up so that such declarations also mangle with a
+      // a private discriminator, in which case this entry point will be called
+      // with the right parameters so that this isn't needed.
+      return (VD->getFormalAccess() <= AccessLevel::FilePrivate &&
+              !VD->hasClangNode());
     });
     results.erase(newEnd, results.end());
 
diff --git a/lib/IRGen/IRGenDebugInfo.cpp b/lib/IRGen/IRGenDebugInfo.cpp
index aa48bdea6b9a3..7a1d258e472f4 100644
--- a/lib/IRGen/IRGenDebugInfo.cpp
+++ b/lib/IRGen/IRGenDebugInfo.cpp
@@ -1075,12 +1075,11 @@ class IRGenDebugInfoImpl : public IRGenDebugInfo {
         CanonicalName.clear();
     }
 
-    bool IsTypeOriginallyDefinedIn =
-        containsOriginallyDefinedIn(DbgTy.getType());
-    // TODO(https://github.com/apple/swift/issues/57699): We currently cannot round trip some C++ types.
+    bool IsTypeOriginallyDefinedIn = containsOriginallyDefinedIn(DbgTy.getType());
+    bool IsCxxType = containsCxxType(DbgTy.getType());
     // There's no way to round trip when respecting @_originallyDefinedIn for a type.
-    if (!Opts.DisableRoundTripDebugTypes &&
-        !Ty->getASTContext().LangOpts.EnableCXXInterop && !IsTypeOriginallyDefinedIn) {
+    // TODO(https://github.com/apple/swift/issues/57699): We currently cannot round trip some C++ types.
+    if (!Opts.DisableRoundTripDebugTypes && !IsTypeOriginallyDefinedIn && !IsCxxType) {
       // Make sure we can reconstruct mangled types for the debugger.
       auto &Ctx = Ty->getASTContext();
       Type Reconstructed = Demangle::getTypeForMangling(Ctx, SugaredName, Sig);
@@ -2504,6 +2503,42 @@ class IRGenDebugInfoImpl : public IRGenDebugInfo {
     return Walker.visitedOriginallyDefinedIn;
   }
 
+  /// Returns true if the type contains an imported C++ type. Due to
+  /// various unimplemented features these cannot round-trip through
+  /// the ASTDemangler.
+  ///
+  /// FIXME: Get these cases working with the ASTDemangler instead.
+  bool containsCxxType(Type T) {
+    return T.findIf([&](Type t) -> bool {
+      if (auto *decl = t->getAnyNominal()) {
+        if (auto *clangDecl = decl->getClangDecl()) {
+          // Lookup of template instantiations is not implemented.
+          if (isa<clang::ClassTemplateSpecializationDecl>(clangDecl))
+            return true;
+
+          // Lookup of types in weird contexts is not implemented.
+          if (isa<clang::EnumDecl>(clangDecl) ||
+              isa<clang::CXXRecordDecl>(clangDecl)) {
+            auto *dc = clangDecl->getDeclContext();
+            while (!isa<clang::TranslationUnitDecl>(dc)) {
+              // ... in namespaces,
+              if (isa<clang::NamespaceDecl>(dc))
+                return true;
+
+              // ... or inside other types.
+              if (isa<clang::CXXRecordDecl>(dc))
+                return true;
+
+              dc = dc->getParent();
+            }
+          }
+        }
+      }
+
+      return false;
+    });
+  }
+
   /// Returns the decl of the type's parent chain annotated by
   /// @_originallyDefinedIn. Returns null if no type is annotated.
   NominalTypeDecl *getDeclAnnotatedByOriginallyDefinedIn(DebugTypeInfo DbgTy) {