Clean up error messages

Some highlights:

- Don't start errors with capital letters or end with periods
- Add 'toml: ' prefix
- Get rid of a recursive Decode error: this becomes excessively long
  without being all that helpful for troubleshooting
- Reword some messages

Updates BurntSushi#60.

decode.go

@@ -10,7 +10,9 @@ import (
 	"time"
 )
 
-var e = fmt.Errorf
+func e(format string, args ...interface{}) error {
+	return fmt.Errorf("toml: "+format, args...)
+}
 
 // Unmarshaler is the interface implemented by objects that can unmarshal a
 // TOML description of themselves.
@@ -105,7 +107,7 @@ func (md *MetaData) PrimitiveDecode(primValue Primitive, v interface{}) error {
 func Decode(data string, v interface{}) (MetaData, error) {
 	rv := reflect.ValueOf(v)
 	if rv.Kind() != reflect.Ptr {
-		return MetaData{}, e("Decode of non-pointer type %s", reflect.TypeOf(v))
+		return MetaData{}, e("Decode of non-pointer %s", reflect.TypeOf(v))
 	}
 	if rv.IsNil() {
 		return MetaData{}, e("Decode of nil %s", reflect.TypeOf(v))
@@ -218,15 +220,15 @@ func (md *MetaData) unify(data interface{}, rv reflect.Value) error {
 	case reflect.Interface:
 		// we only support empty interfaces.
 		if rv.NumMethod() > 0 {
-			return e("Unsupported type '%s'.", rv.Kind())
+			return e("unsupported type %s", rv.Type())
 		}
 		return md.unifyAnything(data, rv)
 	case reflect.Float32:
 		fallthrough
 	case reflect.Float64:
 		return md.unifyFloat64(data, rv)
 	}
-	return e("Unsupported type '%s'.", rv.Kind())
+	return e("unsupported type %s", rv.Kind())
 }
 
 func (md *MetaData) unifyStruct(mapping interface{}, rv reflect.Value) error {
@@ -235,7 +237,8 @@ func (md *MetaData) unifyStruct(mapping interface{}, rv reflect.Value) error {
 		if mapping == nil {
 			return nil
 		}
-		return mismatch(rv, "map", mapping)
+		return e("type mismatch for %s: expected table but found %T",
+			rv.Type().String(), mapping)
 	}
 
 	for key, datum := range tmap {
@@ -260,14 +263,13 @@ func (md *MetaData) unifyStruct(mapping interface{}, rv reflect.Value) error {
 				md.decoded[md.context.add(key).String()] = true
 				md.context = append(md.context, key)
 				if err := md.unify(datum, subv); err != nil {
-					return e("Type mismatch for '%s.%s': %s",
-						rv.Type().String(), f.name, err)
+					return err
 				}
 				md.context = md.context[0 : len(md.context)-1]
 			} else if f.name != "" {
 				// Bad user! No soup for you!
-				return e("Field '%s.%s' is unexported, and therefore cannot "+
-					"be loaded with reflection.", rv.Type().String(), f.name)
+				return e("cannot write unexported field %s.%s",
+					rv.Type().String(), f.name)
 			}
 		}
 	}
@@ -385,15 +387,15 @@ func (md *MetaData) unifyInt(data interface{}, rv reflect.Value) error {
 				// No bounds checking necessary.
 			case reflect.Int8:
 				if num < math.MinInt8 || num > math.MaxInt8 {
-					return e("Value '%d' is out of range for int8.", num)
+					return e("value %d is out of range for int8", num)
 				}
 			case reflect.Int16:
 				if num < math.MinInt16 || num > math.MaxInt16 {
-					return e("Value '%d' is out of range for int16.", num)
+					return e("value %d is out of range for int16", num)
 				}
 			case reflect.Int32:
 				if num < math.MinInt32 || num > math.MaxInt32 {
-					return e("Value '%d' is out of range for int32.", num)
+					return e("value %d is out of range for int32", num)
 				}
 			}
 			rv.SetInt(num)
@@ -404,15 +406,15 @@ func (md *MetaData) unifyInt(data interface{}, rv reflect.Value) error {
 				// No bounds checking necessary.
 			case reflect.Uint8:
 				if num < 0 || unum > math.MaxUint8 {
-					return e("Value '%d' is out of range for uint8.", num)
+					return e("value %d is out of range for uint8", num)
 				}
 			case reflect.Uint16:
 				if num < 0 || unum > math.MaxUint16 {
-					return e("Value '%d' is out of range for uint16.", num)
+					return e("value %d is out of range for uint16", num)
 				}
 			case reflect.Uint32:
 				if num < 0 || unum > math.MaxUint32 {
-					return e("Value '%d' is out of range for uint32.", num)
+					return e("value %d is out of range for uint32", num)
 				}
 			}
 			rv.SetUint(unum)
@@ -503,10 +505,5 @@ func isUnifiable(rv reflect.Value) bool {
 }
 
 func badtype(expected string, data interface{}) error {
-	return e("Expected %s but found '%T'.", expected, data)
-}
-
-func mismatch(user reflect.Value, expected string, data interface{}) error {
-	return e("Type mismatch for %s. Expected %s but found '%T'.",
-		user.Type().String(), expected, data)
+	return e("cannot decode TOML %s into Go value of type %T", expected, data)
 }

decode_test.go

@@ -573,7 +573,7 @@ func TestDecodeBadValues(t *testing.T) {
 		v    interface{}
 		want string
 	}{
-		{3, "non-pointer type"},
+		{3, "non-pointer int"},
 		{(*int)(nil), "nil"},
 	} {
 		_, err := Decode(`x = 3`, tt.v)

encode.go

@@ -16,17 +16,17 @@ type tomlEncodeError struct{ error }
 
 var (
 	errArrayMixedElementTypes = errors.New(
-		"can't encode array with mixed element types")
+		"toml: cannot encode array with mixed element types")
 	errArrayNilElement = errors.New(
-		"can't encode array with nil element")
+		"toml: cannot encode array with nil element")
 	errNonString = errors.New(
-		"can't encode a map with non-string key type")
+		"toml: cannot encode a map with non-string key type")
 	errAnonNonStruct = errors.New(
-		"can't encode an anonymous field that is not a struct")
+		"toml: cannot encode an anonymous field that is not a struct")
 	errArrayNoTable = errors.New(
-		"TOML array element can't contain a table")
+		"toml: TOML array element cannot contain a table")
 	errNoKey = errors.New(
-		"top-level values must be a Go map or struct")
+		"toml: top-level values must be Go maps or structs")
 	errAnything = errors.New("") // used in testing
 )
 
@@ -148,7 +148,7 @@ func (enc *Encoder) encode(key Key, rv reflect.Value) {
 	case reflect.Struct:
 		enc.eTable(key, rv)
 	default:
-		panic(e("Unsupported type for key '%s': %s", key, k))
+		panic(e("unsupported type for key '%s': %s", key, k))
 	}
 }
 
@@ -191,7 +191,7 @@ func (enc *Encoder) eElement(rv reflect.Value) {
 	case reflect.String:
 		enc.writeQuoted(rv.String())
 	default:
-		panic(e("Unexpected primitive type: %s", rv.Kind()))
+		panic(e("unexpected primitive type: %s", rv.Kind()))
 	}
 }