[lldb] Diagnose a fallback warning for type aliases

Author: adrian-prantl

lldb/source/Plugins/LanguageRuntime/Swift/SwiftLanguageRuntimeDynamicTypeResolution.cpp

@@ -3309,6 +3309,11 @@ SwiftLanguageRuntime::GetSwiftRuntimeTypeInfo(
 
   // Resolve all type aliases.
   type = type.GetCanonicalType();
+  if (!type)
+    // FIXME: We could print a better error message if
+    // GetCanonicalType() returned an Expected.
+    return llvm::createStringError(
+        "could not get canonical type (possibly due to unresolved typealias)");
 
   // Resolve all generic type parameters in the type for the current
   // frame. Generic parameter binding has to happen in the scratch

lldb/source/Plugins/TypeSystem/Swift/TypeSystemSwiftTypeRef.cpp

@@ -3383,7 +3383,11 @@ TypeSystemSwiftTypeRef::GetCanonicalType(opaque_compiler_type_t type) {
       // then we don't have debug info to resolve it from.
       CompilerType ast_type =
         ReconstructType({weak_from_this(), type}, nullptr).GetCanonicalType();
-      return GetTypeFromMangledTypename(ast_type.GetMangledTypeName());
+      CompilerType result =
+          GetTypeFromMangledTypename(ast_type.GetMangledTypeName());
+      if (result && !llvm::isa<TypeSystemSwiftTypeRefForExpressions>(this))
+        DiagnoseSwiftASTContextFallback(__FUNCTION__, type);
+      return result;
     }
     auto flavor = SwiftLanguageRuntime::GetManglingFlavor(AsMangledName(type));
     auto mangling = mangleNode(canonical, flavor);