enforceNestingLimit (Parser.Events.swift) bounds PHYSICAL collection
depth in the raw event stream, since it counts sequenceStart/
mappingStart events directly. It does nothing against an
anchor-expansion bomb: a handful of shallow, small anchors each
aliased many times, each alias nested inside the next, keeps raw
event depth at a constant 2 per line while the LOGICAL tree an alias
resolves to grows exponentially in the number of alias levels. A
25-level, fan-out-9 document (~1.5KB) expands past 9^25 logical
nodes; before this fix, parse accepted it in under 2ms, and any
full-tree walk downstream (JSON representability checking, JSON
writing, validation) never terminated.
Added a total expanded-node budget, charged incrementally as the
document streams through the composer rather than by walking
anything: every scalar charges 1, every completed container charges 1
for its own wrapper (children already charged their own cost as they
completed), and every alias resolution charges the target's CACHED
expanded size -- computed once when the anchor was defined, looked up
in O(1). This makes a nested bomb's true compounded size visible
arithmetically within a few alias levels, without ever materializing
or walking the exponential tree it would otherwise produce. A
document with genuinely wide but non-exponential alias reuse (the
same small anchor referenced thousands of times at one level, no
nesting) stays comfortably inside the budget and parses normally.
Verified via the full existing test suite (674 tests, all passing,
zero regressions -- including the YAML Test Suite conformance corpus
and the tagged round-trip corpus), two new tests proving the bomb is
rejected (in under 2ms) and that wide non-exponential fan-out still
parses, and swiftformat/swiftlint --strict clean on all five touched
files.
PureYAML.Parsing.EventComposer and Tagged.EventComposer (two other,
separate composer implementations in this package, used by the
diagnostic-validation and tagged-parsing entry points respectively)
share the same architectural gap and would benefit from the same
fix, but are not reachable from the confirmed exploit path this
change closes -- disclosed, not fixed here.
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).
Split the six files that declared multiple sibling types under one
namespace extension so each file declares exactly one top-level type:
the Tagged node component types (Node, NodeKind, Scalar, Sequence,
Mapping, Pair), the validation report types (Report, Source,
SourceReport, BatchReport), DiagnosticKind, TokenKind, ScannerFlowContext
kind, and the event-stream composer helpers. Public type names are
unchanged; the shared report-rendering helpers move from file-private to
internal so the split report types still reach them.
Make check-namespacing.sh namespace-aware: the previous column-anchored
scan was blind to types declared inside indented extension blocks, so it
passed while the rule was violated. It now counts direct members of a
PureYAML namespace extension and ignores nested types and private helpers.
