An attribute node's document-order key bands by the attribute's index among its
owner's attributes, found with owner.attributes.firstIndex { $0.name == name }.
That linear scan ran for every attribute node, so sorting an element's K
attributes into document order was O(K^2): an 8000-attribute element took ~0.18s
and grew quadratically.
Cache a per-owner attribute-name-to-index map in SiblingIndexCache, built once
on the second lookup (a single lookup still scans), exactly as the sibling-index
cache already does for child positions. The index is the same first-occurrence
position; only its cost changes.
The 8000-attribute sort drops to ~0.01s (~16x) and is now linear. The full
suite, the W3C XPath and Apache Xalan corpora, the C14N suite (which orders
attributes byte-exactly), and the WASM build stay green; AttributeDocumentOrderTests
pins declaration order through the cached sort.
EventReader.next(), both initializers, and the Event alias are public
(an internal typealias in a split file had been shadowing the public
Parsing.Event); a new PureXMLPublicAPITests target compiles without
testable import so facade gaps fail CI. The large-corpus benchmarks
exposed document-order sorting as quadratic on flat fan-outs; the fix's
first attempt was itself worse (an eager sibling table built per
predicate evaluation), caught by sampling the live run, and replaced
with a lazy table: single-node sets never touch order keys and a
parent's table builds on its second lookup. XPath at 42 MB drops
27.1 s to 1.57 s (190x to 11.7x); at 210 MB PureXML completes in 9.4 s
the query libxml2 refuses at its 10M node-set cap (#143 tracks our
configurable budget). Benchmark harness: size series to 210 MB, CORPUS
mode for real files (NASA, SwissProt measured), SAX stage,
refusal-aware table, NULL-safe C driver. All conformance suites,
Linux, and WASM verified. Closes#142.
