table: interfaces: unique gen_types

vlib/v/table/table.v

@@ -490,7 +490,9 @@ pub fn (t &Table) check(got, expected Type) bool {
 		mut info := exp_type_sym.info as Interface
 		// println('gen_types before')
 		// println(info.gen_types)
-		info.gen_types << got_type_sym.name
+		if got_type_sym.name !in info.gen_types {
+			info.gen_types << got_type_sym.name
+		}
 		// println('adding gen_type $got_type_sym.name')
 		// println(info.gen_types)
 		return true

vlib/v/tests/interface_test.v

@@ -46,6 +46,7 @@ fn test_perform_speak() {
 	perform_speak(dog)
 	cat := Cat{}
 	perform_speak(cat)
+	perform_speak(Cat{})
 	perform_speakers([dog, cat])
 	/*
 	f := Foo {