Fix parsing of multi line text (#590)

* fix parser of flow sequence
* support line folded
* update test cases
* refactor
* fix literal-scalars
* remove unnecessary indent state updater

parser/parser.go

@@ -1016,6 +1016,9 @@ func (p *parser) parseFlowSequence(ctx *context) (*ast.SequenceNode, error) {
 		}
 
 		if tk.Type() == token.CollectEntryType {
+			if isFirst {
+				return nil, errors.ErrSyntax("expected sequence element, but found ','", tk.RawToken())
+			}
 			ctx.goNext()
 		} else if !isFirst {
 			return nil, errors.ErrSyntax("',' or ']' must be specified", tk.RawToken())

parser/parser_test.go

@@ -1236,7 +1236,7 @@ b: - 2
 		{
 			">\n>",
 			`
-[2:1] could not find document
+[2:1] could not find multi line content
    1 | >
 >  2 | >
        ^
@@ -1245,7 +1245,7 @@ b: - 2
 		{
 			">\n1",
 			`
-[2:1] could not find document
+[2:1] could not find multi line content
    1 | >
 >  2 | 1
        ^
@@ -1254,7 +1254,7 @@ b: - 2
 		{
 			"|\n1",
 			`
-[2:1] could not find document
+[2:1] could not find multi line content
    1 | |
 >  2 | 1
        ^
@@ -1263,7 +1263,7 @@ b: - 2
 		{
 			"a: >3\n  1",
 			`
-[2:3] invalid number of indent is specified in the document header
+[2:3] invalid number of indent is specified in the multi line header
    1 | a: >3
 >  2 |   1
          ^