Valid YAML fails to parse when comment handling is enabled

Given the input:

# on list
[
    # first
    'first entry',
    # second
    'second entry'
]

the parser will fail when ScannerImpl.emitComments is true, with the following error message:

<org.yaml.snakeyaml.events.StreamStartEvent()>
<org.yaml.snakeyaml.events.CommentEvent(type=BLOCK, value= on list)>
<org.yaml.snakeyaml.events.DocumentStartEvent()>
<org.yaml.snakeyaml.events.SequenceStartEvent(anchor=null, tag=null, implicit=true)>
<org.yaml.snakeyaml.events.CommentEvent(type=BLOCK, value= first)>
Caught: while parsing a flow node
 in 'string', line 4, column 18:
        'first entry',
                     ^
expected the node content, but found ','
 in 'string', line 4, column 18:
        'first entry',
                     ^

while parsing a flow node
 in 'string', line 4, column 18:
        'first entry',
                     ^
expected the node content, but found ','
 in 'string', line 4, column 18:
        'first entry',
                     ^

        at org.yaml.snakeyaml.parser.ParserImpl.parseNode(ParserImpl.java:521)
        at org.yaml.snakeyaml.parser.ParserImpl.parseFlowNode(ParserImpl.java:401)
        at org.yaml.snakeyaml.parser.ParserImpl.access$2600(ParserImpl.java:121)
        at org.yaml.snakeyaml.parser.ParserImpl$ParseFlowSequenceEntry.produce(ParserImpl.java:769)
        at org.yaml.snakeyaml.parser.ParserImpl$ParseFlowSequenceFirstEntry.produce(ParserImpl.java:738)
        at org.yaml.snakeyaml.parser.ParserImpl.peekEvent(ParserImpl.java:166)
        at org.yaml.snakeyaml.parser.Parser$peekEvent$0.call(Unknown Source)
        at test.run(test.groovy:29)
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)

I’ve tested this building off of your commit c42e19bcec6c003befa1dc05ac21eab5f92b13d6, using the following groovy script (run with groovy -cp snakeyaml/target/snakeyaml-1.30-SNAPSHOT.jar test.groovy:

import org.yaml.snakeyaml.parser.ParserImpl
import org.yaml.snakeyaml.reader.StreamReader
import org.yaml.snakeyaml.scanner.ScannerImpl

def contents = """\
# on list
[
    # first
    'first entry',
    # second
    'second entry'
]
"""

// Print events
def scanner = new ScannerImpl(new StreamReader(contents))

scanner.emitComments = true // Causes a failure
def parser = new ParserImpl(scanner)
do {
    println parser.getEvent()
} while (parser.peekEvent())

‌

When removing the scanner.emitComments = true line, this text parses fine but comments are not handled (as expected).

I’ve been experimenting with applying the new comment handling to my application – some earlier work suggests https://github.com/SpongePowered/Configurate/blob/1d788e89b799c129df6ba8c1c66edde183a1a188/vendor/snakeyaml-patches/0001-parser-More-tests-for-comment-reading.patch will resolve the issue, but I’m not sure if my fix was the “correct” way. Feel free to use anything there (or in any of my other patches) that is useful to you.

With that patch applied, the event stream looks like this:

<org.yaml.snakeyaml.events.StreamStartEvent()>
<org.yaml.snakeyaml.events.CommentEvent(type=BLOCK, value= on list)>
<org.yaml.snakeyaml.events.DocumentStartEvent()>
<org.yaml.snakeyaml.events.SequenceStartEvent(anchor=null, tag=null, implicit=true)>
<org.yaml.snakeyaml.events.CommentEvent(type=BLOCK, value= first)>
<org.yaml.snakeyaml.events.ScalarEvent(anchor=null, tag=null, implicit=[false, true], value=first entry)>
<org.yaml.snakeyaml.events.CommentEvent(type=BLOCK, value= second)>
<org.yaml.snakeyaml.events.ScalarEvent(anchor=null, tag=null, implicit=[false, true], value=second entry)>
<org.yaml.snakeyaml.events.SequenceEndEvent()>
<org.yaml.snakeyaml.events.DocumentEndEvent()>
<org.yaml.snakeyaml.events.StreamEndEvent()>

This matches what I would expect.

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