The validation module already implemented the composable-rule idiom under
its own names (Check/Issue/SubjectContext) and a value-type Validator with
duplicated traversal machinery per layer. Renamed the core types to the
canonical names (Validation/ValidationError/ValidationErrorCollection/
ValidationContext/BuiltinValidation/AnyValidation), converted Validator to
a reference-type class with the two-tier default-rule split, and genericized
it over both Subject and Document via a new Traversable protocol so the
model and tagged layers share one walk engine instead of two copies. Wired
the JSON-representability rule set into the same shape and closed the two
missing pieces (unwrap combinator, JSON coverage/config-pin tests).
Tagged.Scalar/Sequence/Mapping gain anchor and style fields
(Tagged.ScalarStyle, Tagged.CollectionStyle), Tagged.Node gains an
alias(anchor:node:) case carrying both the reference and its resolution,
and parseTagged populates all of it from the parse events instead of
discarding anchors and expanding aliases into copies.
PureYAML.dump(_ node: Tagged.Node, options:) re-emits anchors, alias
references, tags, and per-node styles over the document-wide policy.
Plain scalars re-emit their source spelling (NO stays NO, an empty null
stays empty); literal blocks cover keep chomping, single-line strip
chomping, leading blank lines, and whitespace-led first lines via an
explicit indentation indicator; folded scalars re-emit as > when the
folding rules invert exactly and degrade to a literal block otherwise.
The round-trip law parseTagged(dump(parseTagged(d))) == parseTagged(d)
is corpus-tested over every real-world fixture, with one documented
degradation: single-quoted content containing line breaks re-emits
double-quoted, value unchanged.
Closes#9
Port the located value tree onto the hand-rolled engine, reusing the
engine-agnostic located layer (Model.LocatedValue, LocatedPair,
SourcePosition, SourceRange, and the located composer helper) authored
on the conformance branch. The streaming composer now builds a parallel
located tree behind an opt-in tracksLocations flag, exposed as
parseLocated / parseStreamLocated; the plain Value path stays
byte-identical, gated behind the flag.
The scalar event carries the scanner token's end mark, so a located
scalar spans the whole token (end exclusive, one past the last
character) rather than being start-anchored. The hand-rolled scanner
already tracked token end marks, so this surfaces information the engine
was already computing.
Also stop emitting a spurious null document for a comment-only or empty
stream: YAML 1.2 gives such a stream zero documents, while the
single-document value API still maps it to null, so parse("") is
unchanged.
A whole-suite test proves the located projection equals a plain parse
for every passing case; the value, event-dump, and conformance suites
stay green (507 tests).
