parser: fix interface functions with no params (ui examples)

vlib/v/parser/fn.v

@@ -367,7 +367,8 @@ fn (mut p Parser) fn_args() ([]table.Arg, bool, bool) {
 	mut args := []table.Arg{}
 	mut is_variadic := false
 	// `int, int, string` (no names, just types)
-	types_only := p.tok.kind in [.amp, .ellipsis, .key_fn] || (p.peek_tok.kind in [.comma, .rpar] && p.table.known_type(p.tok.lit))
+	types_only := p.tok.kind in [.amp, .ellipsis, .key_fn] || (p.peek_tok.kind == .comma && p.table.known_type(p.tok.lit)) ||
+		p.peek_tok.kind == .rpar
 	// TODO copy pasta, merge 2 branches
 	if types_only {
 		// p.warn('types only')

vlib/v/parser/tests/fn_type_only_args_in_interfaces.out

@@ -0,0 +1,5 @@
+vlib/v/parser/tests/fn_type_only_args_in_interfaces.v:22:1: error: `syntax_error` evaluated but not used 
+   20 | }
+   21 | 
+   22 | syntax_error
+      | ~~~~~~~~~~~~

vlib/v/parser/tests/fn_type_only_args_in_interfaces.vv

@@ -0,0 +1,22 @@
+
+struct Type1 {}
+struct Type2 {}
+struct Type3 {}
+
+
+pub interface Widget1 {
+  init(Type1, Type2)
+}
+
+pub interface Widget2 {
+  init(Type1)
+  draw(Type2, Type3)
+}
+
+pub interface Widget3 {
+  fnoparams1()
+  fnoparams2()
+  draw(Type1, Type2)
+}
+
+syntax_error

vlib/v/parser/tests/fn_type_only_args_unknown_name.out

@@ -1,5 +1,6 @@
-vlib/v/parser/tests/fn_type_only_args_unknown_name.v:1:16: error: unexpected `{`, expecting `,` 
+vlib/v/parser/tests/fn_type_only_args_unknown_name.v:2:1: error: functions with type only args can not have bodies 
     1 | fn test(param) {
-      |                ^
     2 | }
+      | ^
     3 | 
+    4 | fn main() {