A mapping value's anchor or tag on the line below the key must be indented
past the key. The parser consumed such a property regardless of its column,
so 'seq:' then '&anchor' in column 1, anchoring a sequence at the document
level, parsed instead of failing.
When the value's properties are consumed before the indent check, a
properly indented one would have been preceded by an indent token and
consumed inside the indented value; reaching that point with a property on
a later line therefore means it sits at the key's indentation, which is
rejected. The indented-value branch and the new guard move to their own
helpers so parseMappingPair stays within the complexity and length limits.
An inline property, an indented property, and a block sequence at the key's
indent are unaffected.
Measured against the official YAML test-suite, parse-level conformance
rises from 275/333 (82.6%) to 276/333 (82.9%) with no regression.
Mihaela M
ecf634fdf7