support FormatErrorWithToken function for custom error message (#677)

Author: goccy

error.go

@@ -16,6 +16,7 @@ var (
 	ErrInvalidCommentMapValue     = errors.New("invalid comment map value. it must be not nil value")
 	ErrDecodeRequiredPointerType  = errors.New("required pointer type value")
 	ErrExceededMaxDepth           = errors.New("exceeded max depth")
+	FormatErrorWithToken          = errors.FormatError
 )
 
 type (
@@ -25,6 +26,7 @@ type (
 	DuplicateKeyError       = errors.DuplicateKeyError
 	UnknownFieldError       = errors.UnknownFieldError
 	UnexpectedNodeTypeError = errors.UnexpectedNodeTypeError
+	Error                   = errors.Error
 )
 
 func ErrUnsupportedHeadPositionType(node ast.Node) error {

internal/errors/error.go

@@ -21,10 +21,22 @@ const (
 	defaultIncludeSource = true
 )
 
-type PrettyFormatError interface {
+type Error interface {
+	error
+	GetToken() *token.Token
+	GetMessage() string
 	FormatError(bool, bool) string
 }
 
+var (
+	_ Error = new(SyntaxError)
+	_ Error = new(TypeError)
+	_ Error = new(OverflowError)
+	_ Error = new(DuplicateKeyError)
+	_ Error = new(UnknownFieldError)
+	_ Error = new(UnexpectedNodeTypeError)
+)
+
 type SyntaxError struct {
 	Message string
 	Token   *token.Token
@@ -109,20 +121,40 @@ func ErrUnexpectedNodeType(actual, expected ast.NodeType, tk *token.Token) *Unex
 	}
 }
 
+func (e *SyntaxError) GetMessage() string {
+	return e.Message
+}
+
+func (e *SyntaxError) GetToken() *token.Token {
+	return e.Token
+}
+
 func (e *SyntaxError) Error() string {
 	return e.FormatError(defaultFormatColor, defaultIncludeSource)
 }
 
 func (e *SyntaxError) FormatError(colored, inclSource bool) string {
-	return formatError(e.Message, e.Token, colored, inclSource)
+	return FormatError(e.Message, e.Token, colored, inclSource)
+}
+
+func (e *OverflowError) GetMessage() string {
+	return e.msg()
+}
+
+func (e *OverflowError) GetToken() *token.Token {
+	return e.Token
 }
 
 func (e *OverflowError) Error() string {
 	return e.FormatError(defaultFormatColor, defaultIncludeSource)
 }
 
 func (e *OverflowError) FormatError(colored, inclSource bool) string {
-	return formatError(fmt.Sprintf("cannot unmarshal %s into Go value of type %s ( overflow )", e.SrcNum, e.DstType), e.Token, colored, inclSource)
+	return FormatError(e.msg(), e.Token, colored, inclSource)
+}
+
+func (e *OverflowError) msg() string {
+	return fmt.Sprintf("cannot unmarshal %s into Go value of type %s ( overflow )", e.SrcNum, e.DstType)
 }
 
 func (e *TypeError) msg() string {
@@ -132,39 +164,75 @@ func (e *TypeError) msg() string {
 	return fmt.Sprintf("cannot unmarshal %s into Go value of type %s", e.SrcType, e.DstType)
 }
 
+func (e *TypeError) GetMessage() string {
+	return e.msg()
+}
+
+func (e *TypeError) GetToken() *token.Token {
+	return e.Token
+}
+
 func (e *TypeError) Error() string {
 	return e.FormatError(defaultFormatColor, defaultIncludeSource)
 }
 
 func (e *TypeError) FormatError(colored, inclSource bool) string {
-	return formatError(e.msg(), e.Token, colored, inclSource)
+	return FormatError(e.msg(), e.Token, colored, inclSource)
+}
+
+func (e *DuplicateKeyError) GetMessage() string {
+	return e.Message
+}
+
+func (e *DuplicateKeyError) GetToken() *token.Token {
+	return e.Token
 }
 
 func (e *DuplicateKeyError) Error() string {
 	return e.FormatError(defaultFormatColor, defaultIncludeSource)
 }
 
 func (e *DuplicateKeyError) FormatError(colored, inclSource bool) string {
-	return formatError(e.Message, e.Token, colored, inclSource)
+	return FormatError(e.Message, e.Token, colored, inclSource)
+}
+
+func (e *UnknownFieldError) GetMessage() string {
+	return e.Message
+}
+
+func (e *UnknownFieldError) GetToken() *token.Token {
+	return e.Token
 }
 
 func (e *UnknownFieldError) Error() string {
 	return e.FormatError(defaultFormatColor, defaultIncludeSource)
 }
 
 func (e *UnknownFieldError) FormatError(colored, inclSource bool) string {
-	return formatError(e.Message, e.Token, colored, inclSource)
+	return FormatError(e.Message, e.Token, colored, inclSource)
+}
+
+func (e *UnexpectedNodeTypeError) GetMessage() string {
+	return e.msg()
+}
+
+func (e *UnexpectedNodeTypeError) GetToken() *token.Token {
+	return e.Token
 }
 
 func (e *UnexpectedNodeTypeError) Error() string {
 	return e.FormatError(defaultFormatColor, defaultIncludeSource)
 }
 
 func (e *UnexpectedNodeTypeError) FormatError(colored, inclSource bool) string {
-	return formatError(fmt.Sprintf("%s was used where %s is expected", e.Actual.YAMLName(), e.Expected.YAMLName()), e.Token, colored, inclSource)
+	return FormatError(e.msg(), e.Token, colored, inclSource)
+}
+
+func (e *UnexpectedNodeTypeError) msg() string {
+	return fmt.Sprintf("%s was used where %s is expected", e.Actual.YAMLName(), e.Expected.YAMLName())
 }
 
-func formatError(errMsg string, token *token.Token, colored, inclSource bool) string {
+func FormatError(errMsg string, token *token.Token, colored, inclSource bool) string {
 	var pp printer.Printer
 	pos := fmt.Sprintf("[%d:%d] ", token.Position.Line, token.Position.Column)
 	msg := pp.PrintErrorMessage(fmt.Sprintf("%s%s", pos, errMsg), colored)

yaml.go

@@ -222,9 +222,9 @@ func NodeToValue(node ast.Node, v interface{}, opts ...DecodeOption) error {
 // If the third argument `inclSource` is true, the error message will
 // contain snippets of the YAML source that was used.
 func FormatError(e error, colored, inclSource bool) string {
-	var pe errors.PrettyFormatError
-	if errors.As(e, &pe) {
-		return pe.FormatError(colored, inclSource)
+	var yamlErr Error
+	if errors.As(e, &yamlErr) {
+		return yamlErr.FormatError(colored, inclSource)
 	}
 
 	return e.Error()

yaml_test.go

@@ -8,6 +8,7 @@ import (
 	"testing"
 
 	"github.com/goccy/go-yaml"
+	"github.com/goccy/go-yaml/parser"
 )
 
 func TestRoundTripWithComment(t *testing.T) {
@@ -229,3 +230,34 @@ i:
 		t.Fatalf("failed to encode: %s", string(got))
 	}
 }
+
+func TestCustomErrorMessage(t *testing.T) {
+	data := `
+foo:
+  bar:
+    foo: 2
+  baz:
+    foo: 3
+foo: 2
+`
+	if _, err := parser.ParseBytes([]byte(data), 0); err == nil {
+		t.Fatalf("expected error")
+	} else {
+		yamlErr, ok := err.(yaml.Error)
+		if !ok {
+			t.Fatalf("failed to get yaml.Error from error: %T", err)
+		}
+		expected := `
+[7:1] custom message
+   4 |     foo: 2
+   5 |   baz:
+   6 |     foo: 3
+>  7 | foo: 2
+       ^
+`
+		got := "\n" + yaml.FormatErrorWithToken("custom message", yamlErr.GetToken(), false, true)
+		if expected != got {
+			t.Fatalf("unexpected error message:\nexpected:\n%s\nbut got:\n%s", expected, got)
+		}
+	}
+}