checker: prevent double module name prepending on generics types regi… (#9791)

vlib/v/checker/checker.v

@@ -1929,7 +1929,7 @@ pub fn (mut c Checker) fn_call(mut call_expr ast.CallExpr) ast.Type {
 		}
 	}
 	if has_generic_generic {
-		if c.mod != '' {
+		if c.mod != '' && !fn_name.starts_with('${c.mod}.') {
 			// Need to prepend the module when adding a generic type to a function
 			c.table.register_fn_generic_types(c.mod + '.' + fn_name, generic_types)
 		} else {

vlib/v/tests/generics_in_generics_test.v

@@ -0,0 +1,12 @@
+fn gen_fn2<T>(e T) string {
+	return '$e.str()'
+}
+
+fn gen_fn<T>(e T) string {
+	return gen_fn2<T>(e)
+}
+
+fn test_generics_in_generics() {
+	assert gen_fn(u64(42)) == '42'
+	assert gen_fn('42') == '42'
+}