Support suffix keyword for document header option

lexer/lexer_test.go

@@ -2149,6 +2149,29 @@ s: >-3
 				},
 			},
 		},
+		{
+			YAML: `
+|2-
+
+                  text
+`,
+			Tokens: token.Tokens{
+				{
+					Type:          token.LiteralType,
+					CharacterType: token.CharacterTypeIndicator,
+					Indicator:     token.BlockScalarIndicator,
+					Value:         "|2-",
+					Origin:        "\n|2-\n",
+				},
+				{
+					Type:          token.StringType,
+					CharacterType: token.CharacterTypeMiscellaneous,
+					Indicator:     token.NotIndicator,
+					Value:         "\n                text",
+					Origin:        "\n                  text\n",
+				},
+			},
+		},
 	}
 	for _, test := range tests {
 		t.Run(test.YAML, func(t *testing.T) {

scanner/context.go

@@ -104,9 +104,12 @@ func (c *Context) updateDocumentIndentColumn() {
 }
 
 func (c *Context) docFirstLineIndentColumnByDocOpt() int {
-	trimmed := strings.TrimPrefix(c.docOpt, "-")
-	trimmed = strings.TrimPrefix(trimmed, "+")
-	i, _ := strconv.ParseInt(trimmed, 10, 64)
+	opt := c.docOpt
+	opt = strings.TrimPrefix(opt, "-")
+	opt = strings.TrimPrefix(opt, "+")
+	opt = strings.TrimSuffix(opt, "-")
+	opt = strings.TrimSuffix(opt, "+")
+	i, _ := strconv.ParseInt(opt, 10, 64)
 	return int(i)
 }
 
@@ -270,7 +273,7 @@ func (c *Context) existsBuffer() bool {
 
 func (c *Context) bufferedSrc() []rune {
 	src := c.buf[:c.notSpaceCharPos]
-	if c.isDocument() && strings.HasPrefix(c.docOpt, "-") {
+	if c.isDocument() && (strings.HasPrefix(c.docOpt, "-") || strings.HasSuffix(c.docOpt, "-")) {
 		// remove end '\n' character and trailing empty lines
 		// https://yaml.org/spec/1.2.2/#8112-block-chomping-indicator
 		for {

scanner/scanner.go

@@ -833,9 +833,10 @@ func (s *Scanner) validateDocumentHeaderOption(opt string) error {
 	if len(opt) == 0 {
 		return nil
 	}
-	if opt[0] == '+' || opt[0] == '-' {
-		opt = opt[1:]
-	}
+	opt = strings.TrimPrefix(opt, "-")
+	opt = strings.TrimPrefix(opt, "+")
+	opt = strings.TrimSuffix(opt, "-")
+	opt = strings.TrimSuffix(opt, "+")
 	if len(opt) == 0 {
 		return nil
 	}