[lldb][DWARFASTParserClang] Don't complete conflicting Objective-C++ types

lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.cpp

@@ -40,6 +40,7 @@
 #include "lldb/Utility/LLDBAssert.h"
 #include "lldb/Utility/Log.h"
 #include "lldb/Utility/StreamString.h"
+#include "lldb/lldb-enumerations.h"
 
 #include "clang/AST/CXXInheritance.h"
 #include "clang/AST/Decl.h"
@@ -2204,6 +2205,22 @@ bool DWARFASTParserClang::CompleteRecordType(const DWARFDIE &die,
   if (attrs.is_forward_declaration)
     return true;
 
+  const bool type_is_objc_object_or_interface =
+      TypeSystemClang::IsObjCObjectOrInterfaceType(clang_type);
+  if (!type_is_objc_object_or_interface &&
+      Language::LanguageIsObjC(
+          static_cast<LanguageType>(die.GetAttributeValueAsUnsigned(
+              DW_AT_APPLE_runtime_class, eLanguageTypeUnknown)))) {
+    // The forward declaration was C++ but the definition is Objective-C.
+    // We currently don't handle such situations. Keep the forward declaration
+    // without a definition.
+    LLDB_LOG(GetLog(LLDBLog::Expressions),
+             "WARNING: Type completion aborted because forward declaration for "
+             "'{0}' is C++ while definition is Objective-C.",
+             attrs.name.AsCString(""));
+    return false;
+  }
+
   clang::DeclContext *decl_ctx = GetClangDeclContextContainingDIE(die, nullptr);
 
   // Start the definition if the type is not being defined already. This can
@@ -2231,9 +2248,6 @@ bool DWARFASTParserClang::CompleteRecordType(const DWARFDIE &die,
                     default_accessibility, layout_info);
 
   // Now parse any methods if there were any...
-  const bool type_is_objc_object_or_interface =
-      TypeSystemClang::IsObjCObjectOrInterfaceType(clang_type);
-  // Now parse any methods if there were any...
   for (const DWARFDIE &mem : member_function_dies)
     dwarf->ResolveType(mem);
 

lldb/test/Shell/SymbolFile/DWARF/objcxx-forward-decls.test

@@ -0,0 +1,70 @@
+# REQUIRES: system-darwin
+
+# In this test we have two CUs with conflicting forward declaration
+# depending on the CU language (one is C++ and the other is Objective-C++).
+# We are then stopped in the C++ CU and try to print the type, at which
+# point LLDB will try to make it into an Clang AST node. If LLDB were to
+# interpret the type as C++ instead of Objective-C, we'd violate Clang
+# invariants and crash.
+#
+# RUN: split-file %s %t
+# RUN: %clangxx_host -c -g -x objective-c++ %t/request.m -o %t/request_objc.o
+# RUN: %clangxx_host -c -g %t/main.cpp -o %t/main.o
+# RUN: %clangxx_host %t/main.o %t/request_objc.o -framework Foundation -o %t/a.out
+#
+# RUN: %lldb %t/a.out \
+# RUN:    -o "breakpoint set -p return -X main" \
+# RUN:    -o run \
+# RUN:    -o "frame variable r" \
+# RUN:    -o exit | FileCheck %s
+#
+# RUN: dsymutil %t/a.out
+#
+# RUN: %lldb %t/a.out \
+# RUN:    -o "breakpoint set -p return -X main" \
+# RUN:    -o run \
+# RUN:    -o "frame variable r" \
+# RUN:    -o exit | FileCheck %s --check-prefix=CHECK-DSYM
+
+# CHECK:      (lldb) frame variable r
+# CHECK-NEXT: (Request) ::r = (m_request = "Hello, World!")
+
+# CHECK-DSYM:      (lldb) frame variable r
+# CHECK-DSYM-NEXT: (Request) ::r = (m_request = "Hello, World!")
+
+#--- lib.h
+#ifndef LIB_H_IN
+#define LIB_H_IN
+
+#ifdef __OBJC__
+@class NSString;                                               
+#else
+class NSString;
+#endif
+
+struct Request {
+  NSString * m_request = nullptr;
+};
+
+#endif // _H_IN
+
+#--- main.cpp
+#include "lib.h"
+
+void process(Request *);
+
+Request r;
+
+int main() {
+    process(&r);
+    return 0;
+}
+
+#--- request.m
+#import <Foundation/Foundation.h>
+
+#include "lib.h"
+
+void process(Request * r) {
+  r->m_request = @"Hello, World!";
+}