[test] instantiating template multiple times with same types (#756)

Author: Vipul-Cariappa

unittests/CppInterOp/FunctionReflectionTest.cpp

@@ -973,6 +973,56 @@ TYPED_TEST(CppInterOpTest, FunctionReflectionTestInstantiateVariadicFunction) {
             "fixedParam, MyClass args, double args)");
 }
 
+TYPED_TEST(CppInterOpTest, FunctionReflectionTestBestOverloadFunctionMatch0) {
+  // make sure templates are not instantiated multiple times
+  std::vector<Decl*> Decls;
+  std::string code = R"(
+  template <typename T1, typename T2 = int>
+  void Tfn(T1& t1, T2& t2) {}
+  )";
+  GetAllTopLevelDecls(code, Decls);
+  EXPECT_EQ(Decls.size(), 1);
+
+  std::vector<Cpp::TCppFunction_t> candidates;
+  candidates.reserve(Decls.size());
+  for (auto* i : Decls)
+    candidates.push_back(i);
+
+  ASTContext& C = Interp->getCI()->getASTContext();
+
+  std::vector<Cpp::TemplateArgInfo> args0 = {
+      C.getLValueReferenceType(C.DoubleTy).getAsOpaquePtr(),
+      C.getLValueReferenceType(C.IntTy).getAsOpaquePtr(),
+  };
+
+  std::vector<Cpp::TemplateArgInfo> explicit_args0;
+  std::vector<Cpp::TemplateArgInfo> explicit_args1 = {
+      C.DoubleTy.getAsOpaquePtr()};
+  std::vector<Cpp::TemplateArgInfo> explicit_args2 = {
+      C.DoubleTy.getAsOpaquePtr(),
+      C.IntTy.getAsOpaquePtr(),
+  };
+
+  Cpp::TCppScope_t fn0 =
+      Cpp::BestOverloadFunctionMatch(candidates, explicit_args0, args0);
+  EXPECT_TRUE(fn0);
+
+  Cpp::TCppScope_t fn =
+      Cpp::BestOverloadFunctionMatch(candidates, explicit_args1, args0);
+  EXPECT_EQ(fn, fn0);
+
+  fn = Cpp::BestOverloadFunctionMatch(candidates, explicit_args2, args0);
+  EXPECT_EQ(fn, fn0);
+
+  fn = Cpp::InstantiateTemplate(Decls[0], explicit_args1.data(),
+                                explicit_args1.size());
+  EXPECT_EQ(fn, fn0);
+
+  fn = Cpp::InstantiateTemplate(Decls[0], explicit_args2.data(),
+                                explicit_args2.size());
+  EXPECT_EQ(fn, fn0);
+}
+
 TYPED_TEST(CppInterOpTest, FunctionReflectionTestBestOverloadFunctionMatch1) {
   std::vector<Decl*> Decls;
   std::string code = R"(