fix JitCall codegen for function with lambda as return value (#678)

Author: Vipul-Cariappa

lib/CppInterOp/CppInterOp.cpp

@@ -1966,9 +1966,24 @@ void collect_type_info(const FunctionDecl* FD, QualType& QT,
   PrintingPolicy Policy(C.getPrintingPolicy());
   Policy.SuppressElaboration = true;
   refType = kNotReference;
-  if (QT->isRecordType() && forArgument) {
-    get_type_as_string(QT, type_name, C, Policy);
-    return;
+  if (QT->isRecordType()) {
+    if (forArgument) {
+      get_type_as_string(QT, type_name, C, Policy);
+      return;
+    }
+    if (auto* CXXRD = QT->getAsCXXRecordDecl()) {
+      if (CXXRD->isLambda()) {
+        std::string fn_name;
+        llvm::raw_string_ostream stream(fn_name);
+        Policy.FullyQualifiedName = true;
+        Policy.SuppressUnwrittenScope = true;
+        FD->getNameForDiagnostic(stream, Policy,
+                                 /*Qualified=*/false);
+        type_name = "__internal_CppInterOp::function<decltype(" + fn_name +
+                    ")>::result_type";
+        return;
+      }
+    }
   }
   if (QT->isFunctionPointerType()) {
     std::string fp_typedef_name;
@@ -3223,6 +3238,17 @@ TInterp_t CreateInterpreter(const std::vector<const char*>& Args /*={}*/,
     llvm::cl::ParseCommandLineOptions(NumArgs + 1, Args.get());
   }
 
+  I->declare(R"(
+    namespace __internal_CppInterOp {
+    template <typename Signature>
+    struct function;
+    template <typename Res, typename... ArgTypes>
+    struct function<Res(ArgTypes...)> {
+      typedef Res result_type;
+    };
+    }  // namespace __internal_CppInterOp
+  )");
+
   sInterpreters->emplace_back(I, /*Owned=*/true);
 
   return I;

unittests/CppInterOp/FunctionReflectionTest.cpp

@@ -2154,6 +2154,19 @@ TEST(FunctionReflectionTest, GetFunctionCallWrapper) {
   EXPECT_TRUE(obj);
   Cpp::Destruct(obj, MyNameSpace_TemplatedEnum_instantiated);
   obj = nullptr;
+
+  Cpp::Declare(R"(
+    auto get_fn(int x) { return [x](int y){ return x + y; }; }
+  )");
+
+  Cpp::TCppScope_t get_fn = Cpp::GetNamed("get_fn");
+  EXPECT_TRUE(get_fn);
+
+  auto get_fn_callable = Cpp::MakeFunctionCallable(get_fn);
+  EXPECT_EQ(get_fn_callable.getKind(), Cpp::JitCall::kGenericCall);
+
+  EXPECT_TRUE(Cpp::IsLambdaClass(Cpp::GetFunctionReturnType(get_fn)));
+  EXPECT_FALSE(Cpp::IsLambdaClass(Cpp::GetFunctionReturnType(bar)));
 }
 
 TEST(FunctionReflectionTest, IsConstMethod) {