validation/fix: escape % in Schema.enumError

schema.go

@@ -299,7 +299,7 @@ func (s *Schema) validate(scope []schemaRef, vscope int, spath string, v interfa
 			}
 		}
 		if !matched {
-			errors = append(errors, validationError("enum", s.enumError))
+			errors = append(errors, validationError("enum", "%s", s.enumError))
 		}
 	}
 

schema_test.go

@@ -428,6 +428,22 @@ func TestInvalidJsonTypeError(t *testing.T) {
 	}
 }
 
+func TestPercentInEnumError(t *testing.T) {
+	compiler := jsonschema.NewCompiler()
+	err := compiler.AddResource("test.json", strings.NewReader(`{"type": "string", "enum": ["%"]}`))
+	if err != nil {
+		t.Fatalf("addResource failed. reason: %v\n", err)
+	}
+	schema, err := compiler.Compile("test.json")
+	if err != nil {
+		t.Fatalf("schema compilation failed. reason: %v\n", err)
+	}
+	err = schema.Validate("hello world")
+	if strings.Contains(err.Error(), `"%!"(MISSING)`) {
+		t.Fatalf(`error contains "%%!"(MISSING)`)
+	}
+}
+
 func TestInfiniteLoopError(t *testing.T) {
 	t.Run("compile", func(t *testing.T) {
 		compiler := jsonschema.NewCompiler()