presenter: treat a tab-indented line in a folded scalar as more-indented - #780
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YAML 1.2.2 8.1.3 defines a more-indented ("spaced text") line by production
[175] s-nb-spaced-text, whose leading [33] s-white is a space *or a tab*; the
breaks around such a line are preserved verbatim ([177] b-l-spaced) rather than
folded. getBlockValue() in the parser already tests for both (0x20 or 0x09),
but the presenter tested only for a space, at four sites in foldBlockScalar()
and foldLine(). It therefore doubled breaks the parser keeps literally, adding
one \n per adjacency:
parseEvents/eventsToAst/present of
k: >
<TAB>
detected
emitted a blank line before "detected", so the value went from
"\t\ndetected\n" to "\t\n\ndetected\n". A tab line between two folded lines
cost two extra \n.
Extract the predicate as isMoreIndented() and use it for the prevMoreIndented
seed, the per-line test and the foldLine guard; the fold-point regexp becomes
/ [^ \t]/ so a break is never placed before a tab either (breaking at the space
in "aaa... \tzzz" moved the tab to the start of the next line).
Enumerating every two-line block-scalar body over a 7-line alphabet in both
block styles gave 84 parseable sources: 12 changed value through
present(), all folded style, all involving a tab; literal style was clean
(0/42). All 12 were confirmed against PyYAML 6.0.3 and ruamel.yaml 0.19.1
reading the emitted bytes, and all 12 round-trip after this change. The public
dump() API never enters this path (it quotes tab-containing strings), so it was
unaffected before and after.
puzrin
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Aug 1, 2026
chaiphet6669-afk
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Aug 2, 2026
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Round-tripping
through
parseEvents→eventsToAst→presentemits a blank line beforedetected, so the value goes from"\t\ndetected\n"to"\t\n\ndetected\n"; with the tab line between two folded lines it costs two extra newlines. YAML 1.2.2 §8.1.3 defines a more-indented line by production [175]s-nb-spaced-text, whose leading [33]s-whiteis a space or a tab, and whose surrounding breaks are preserved ([177]b-l-spaced) rather than folded —getBlockValue()in the parser tests for both (0x20 || 0x09), but the presenter tested only for a space, at four sites infoldBlockScalar/foldLine, including the fold-point regexp/ [^ ]/which would break at the space inaaa… \tzzzand move the tab to the start of the next line. Enumerating every two-line block-scalar body over a 7-line alphabet in both block styles gave 84 parseable sources, of which 12 changed value throughpresent()— all folded style, all involving a tab, literal style clean at 0/42; all 12 were confirmed against PyYAML 6.0.3 and ruamel.yaml 0.19.1 reading the emitted bytes, and all 12 round-trip after this change.To be straight about the blast radius:
dump()is not affected, since it routes tab-containing strings to double-quoted or literal style and never enters the folded path (0 of 41 distinct values from the same family broke either way), so this only reaches code that presents a parsed AST — exported and typed, but not documented in the README. I leftdivergedFixturesalone: R4YG'sdumpcomparison still fails after the fix because the suite double-quotes that scalar while js-yaml faithfully keeps>, which is a genuine style divergence. (Its label there is "missing block scalar indent indicator", but a leading tab needs no indicator — indentation auto-detection only counts spaces — so R4YG was really this bug.)npm testgoes from 1613 tests / 1600 pass / 0 fail to 1614 / 1601 / 0 fail with the added case, and reverting each of the four predicates on its own makes that case fail.