parser: check generic receiver method decl has no generic names (fix parts of #9811) (#9819)

vlib/v/parser/fn.v

@@ -221,13 +221,13 @@ fn (mut p Parser) fn_decl() ast.FnDecl {
 		language = rec.language
 	}
 	mut name := ''
+	name_pos := p.tok.position()
 	if p.tok.kind == .name {
-		pos := p.tok.position()
 		// TODO high order fn
 		name = if language == .js { p.check_js_name() } else { p.check_name() }
 		if language == .v && !p.pref.translated && util.contains_capital(name) && !p.builtin_mod {
 			p.error_with_pos('function names cannot contain uppercase letters, use snake_case instead',
-				pos)
+				name_pos)
 			return ast.FnDecl{
 				scope: 0
 			}
@@ -243,7 +243,7 @@ fn (mut p Parser) fn_decl() ast.FnDecl {
 				}
 			}
 			if is_duplicate {
-				p.error_with_pos('duplicate method `$name`', pos)
+				p.error_with_pos('duplicate method `$name`', name_pos)
 				return ast.FnDecl{
 					scope: 0
 				}
@@ -251,7 +251,7 @@ fn (mut p Parser) fn_decl() ast.FnDecl {
 		}
 		// cannot redefine buildin function
 		if !is_method && !p.builtin_mod && name in builtin_functions {
-			p.error_with_pos('cannot redefine builtin function `$name`', pos)
+			p.error_with_pos('cannot redefine builtin function `$name`', name_pos)
 			return ast.FnDecl{
 				scope: 0
 			}
@@ -267,14 +267,19 @@ fn (mut p Parser) fn_decl() ast.FnDecl {
 		p.error_with_pos('cannot overload `!=`, `>`, `<=` and `>=` as they are auto generated from `==` and`<`',
 			p.tok.position())
 	} else {
-		pos := p.tok.position()
+		p.error_with_pos('expecting method name', p.tok.position())
-		p.error_with_pos('expecting method name', pos)
 		return ast.FnDecl{
 			scope: 0
 		}
 	}
 	// <T>
 	generic_names := p.parse_generic_names()
+	// check generic receiver method has no generic names
+	if is_method && rec.typ.has_flag(.generic) && generic_names.len == 0
+		&& p.table.get_type_symbol(rec.typ).kind != .any {
+		p.error_with_pos('generic receiver method `$name` should add generic names, e.g. $name<T>',
+			name_pos)
+	}
 	// Args
 	args2, are_args_type_only, is_variadic := p.fn_args()
 	params << args2

vlib/v/parser/tests/generic_multiple_receiver_method_has_no_generic_names_err.out

@@ -0,0 +1,7 @@
+vlib/v/parser/tests/generic_multiple_receiver_method_has_no_generic_names_err.vv:6:20: error: generic receiver method `poll` should add generic names, e.g. poll<T>
+    4 | }
+    5 |
+    6 | fn (q Queue<A, B>) poll() A {
+      |                    ~~~~
+    7 |     return q.buffer[0]
+    8 | }

vlib/v/parser/tests/generic_multiple_receiver_method_has_no_generic_names_err.vv

@@ -0,0 +1,13 @@
+struct Queue<A, B>{
+	buffer []A
+	size   B
+}
+
+fn (q Queue<A, B>) poll() A {
+	return q.buffer[0]
+}
+
+fn main() {
+	q := Queue<string, int>{}
+	println(q)
+}

vlib/v/parser/tests/generic_receiver_method_has_no_generic_names_err.out

@@ -0,0 +1,7 @@
+vlib/v/parser/tests/generic_receiver_method_has_no_generic_names_err.vv:5:17: error: generic receiver method `poll` should add generic names, e.g. poll<T>
+    3 | }
+    4 |
+    5 | fn (q Queue<T>) poll() T {
+      |                 ~~~~
+    6 |     return q.buffer[0]
+    7 | }

vlib/v/parser/tests/generic_receiver_method_has_no_generic_names_err.vv

@@ -0,0 +1,12 @@
+struct Queue<T>{
+	buffer []T
+}
+
+fn (q Queue<T>) poll() T {
+	return q.buffer[0]
+}
+
+fn main() {
+	q := Queue<int>{}
+	println(q)
+}