checker: fix generics with assign nested generic fn call (#12366)

Author: yuyi98

vlib/v/checker/checker.v

@@ -2888,13 +2888,14 @@ pub fn (mut c Checker) fn_call(mut node ast.CallExpr, mut continue_check &bool)
 		}
 	}
 	// resolve return generics struct to concrete type
-	if func.generic_names.len > 0 && func.return_type.has_flag(.generic) {
+	if func.generic_names.len > 0 && func.return_type.has_flag(.generic)
+		&& c.table.cur_fn.generic_names.len == 0 {
 		node.return_type = c.table.unwrap_generic_type(func.return_type, func.generic_names,
 			concrete_types)
 	} else {
 		node.return_type = func.return_type
 	}
-	if node.concrete_types.len > 0 && func.return_type != 0 {
+	if node.concrete_types.len > 0 && func.return_type != 0 && c.table.cur_fn.generic_names.len == 0 {
 		if typ := c.table.resolve_generic_to_concrete(func.return_type, func.generic_names,
 			concrete_types)
 		{

vlib/v/tests/generics_with_assign_nested_generics_call_test.v

@@ -0,0 +1,37 @@
+struct SSS<T> {
+mut:
+	x T
+}
+
+fn (s SSS<T>) inner() T {
+	return s.x
+}
+
+fn (s SSS<T>) outer() string {
+	ret := s.inner<T>()
+	println(ret)
+	return '$ret'
+}
+
+fn test_generics_with_assign_nested_generic_method_call() {
+	s1 := SSS<int>{100}
+	assert s1.outer() == '100'
+
+	s2 := SSS<string>{'hello'}
+	assert s2.outer() == 'hello'
+}
+
+fn fn_inner<T>(t T) T {
+	return t
+}
+
+fn fn_outer<T>(t T) string {
+	ret := fn_inner<T>(t)
+	println(ret)
+	return '$ret'
+}
+
+fn test_generics_with_assign_nested_generic_fn_call() {
+	assert fn_outer(100) == '100'
+	assert fn_outer('hello') == 'hello'
+}