List expected types in operator type-mismatch error message

onnxruntime/core/graph/graph.cc

@@ -3239,11 +3239,26 @@ Status Graph::InferAndVerifyTypeMatch(Node& node, const OpSchema& op, const Reso
         if (input_type == nullptr) input_type = &null_pointer;
         // Type error in input model/graph.
 
+        // Build a sorted, readable list of the types the operator permits for this input so the
+        // error message tells the user which types are valid instead of only the offending one.
+        std::vector<std::string> permitted_type_strings;
+        permitted_type_strings.reserve(permitted_types.size());
+        for (const auto* permitted_type : permitted_types) {
+          permitted_type_strings.push_back(permitted_type != nullptr ? *permitted_type : "(null)");
+        }
+        std::sort(permitted_type_strings.begin(), permitted_type_strings.end());
+        std::string expected_types_str;
+        for (size_t t = 0; t < permitted_type_strings.size(); ++t) {
+          if (t != 0) expected_types_str += ", ";
+          expected_types_str += permitted_type_strings[t];
+        }
+
         Status status(ONNXRUNTIME, INVALID_GRAPH,
                       "This is an invalid model. "
                       "Type Error: Type '" +
                           *input_type + "' of input parameter (" + input_def->Name() +
-                          ") of operator (" + op.Name() + ") in node (" + node_name + ") is invalid.");
+                          ") of operator (" + op.Name() + ") in node (" + node_name +
+                          ") is invalid. Expected one of the following types: " + expected_types_str + ".");
         return status;
       }
 

onnxruntime/test/ir/graph_test.cc

@@ -1710,6 +1710,32 @@ TEST_F(GraphTest, VariadicOutput) {
   CheckTensorEltType(Z.TypeAsProto(), TensorProto_DataType_FLOAT);
 }
 
+// When an operator receives an input whose type is not one of the operator's permitted
+// types, the resolve error should list the expected types to aid debugging. See issue #4429.
+TEST_F(GraphTest, TypeErrorMessageListsExpectedTypes) {
+  Model model("graph_type_error", false, *logger_);
+  auto& graph = model.MainGraph();
+
+  TypeProto int64_tensor;
+  int64_tensor.mutable_tensor_type()->set_elem_type(TensorProto_DataType_INT64);
+
+  auto& X = graph.GetOrCreateNodeArg("X", &int64_tensor);
+  auto& Y = graph.GetOrCreateNodeArg("Y", nullptr);
+  graph.SetInputs({&X});
+
+  // Sin only supports floating point types, so an int64 input is invalid.
+  graph.AddNode("node_1", "Sin", "node 1.", {&X}, {&Y});
+
+  auto status = graph.Resolve();
+  ASSERT_FALSE(status.IsOK());
+  const std::string msg = status.ErrorMessage();
+  // The existing context is preserved.
+  EXPECT_NE(msg.find("of operator (Sin)"), std::string::npos) << msg;
+  // The improved message lists the operator's permitted types.
+  EXPECT_NE(msg.find("Expected one of the following types:"), std::string::npos) << msg;
+  EXPECT_NE(msg.find("tensor(float)"), std::string::npos) << msg;
+}
+
 // test that we prefer the graph input shape for a non-const initializer (initializer with matching graph input)
 TEST_F(GraphTest, NonConstInitializer) {
   Model model("graph_1", false, *logger_);