Add FlatNode: read-only columnar full-DOM reader (#82)#84
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The fourth reader alongside Node/LazyNode/Cursor: parse(xml, FlatNode) materializes the whole document once into a contiguous store of isbits records (parent/first_child/next_sibling index links, zero-copy byte ranges into the retained source), so building is fast, random access is O(1), and the GC traces a handful of arrays instead of one object per node. Text and attribute values are entity-decoded at access (the has_entities token flag rides the sign bit of the stored length). The builder is the same single visibly-pushdown pass as _parse with the same well-formedness checks at the same token points (shared check functions; identical error messages, asserted by the parity tests). FlatNode == / hash are positional identity — same store, same node (the #83 semantics, debuting on the new reader). Node(flatnode) materializes a subtree as a mutable Node; XML.write accepts FlatNode. O(1) parent and O(depth) 1-arg depth come free from the stored links. Assisted-by: Claude (Anthropic)
The new W3C parity testset asserts FlatNode ≡ Node (decoded trees) on every well-formed document of the pinned conformance suite, and the exact same accept/reject verdict on every not-well-formed one — any divergence between the flat builder and _parse is a named failure. It caught exactly one on first run, on 5 documents (sun/invalid/empty.xml, oasis p15pass1/p18pass1, ibm P15/P20): an empty comment <!----> or CDATA <![CDATA[]]> has value "" on Node but came back nothing on FlatNode, because the record encoded absence as len == 0. Absence is now value_offset == -1 (empty content keeps a real offset with len 0), matching the Node parser on all three states: absent, empty, present. Assisted-by: Claude (Anthropic)
Assisted-by: Claude (Anthropic)
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Codecov Report❌ Patch coverage is
Additional details and impacted files@@ Coverage Diff @@
## v0.5-dev #84 +/- ##
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+ Coverage 94.47% 94.76% +0.28%
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Files 11 12 +1
Lines 1793 2026 +233
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+ Hits 1694 1920 +226
- Misses 99 106 +7
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Implements #82 —
FlatNode, the fourth reader:parse(xml, FlatNode)materializes the whole document once into a contiguous store of isbits records (index links + zero-copy byte ranges into the retained source; text/attribute values entity-decoded at access).Node's read half atCursor's GC cost.Measured in-package on the 13.5 MiB XMark corpus (882k nodes): build 51.6 ms / 35.5 MiB alloc vs
Node117.3 ms / 122.3 MiB — 2.3× faster, 3.4× fewer allocations, matching the validated prototype; GC pressure collapses (the collector traces a handful of arrays instead of ~2.5 objects per node).Guarantees, all test-enforced:
Nodeparser: decoded-equivalent trees on all 776 well-formed documents; identical accept/reject verdicts on all 1257 not-well-formed ones. The parity harness caught (and this PR fixes) one real divergence on first run: empty<!---->/<![CDATA[]]>must be"", notnothing(tri-state record: absent / empty / present).wellformedlevels and identical error messages asparse(_, Node).==/hashonFlatNodeare positional identity (same store, same node) — the Node identity: === and hash redesign (planned for v0.5) #83 semantics, debuting on the new reader;unique/Dictbehave.parent(node), O(depth) 1-argdepth(node);Node(flatnode)materializes a subtree as a mutableNode;XML.writeacceptsFlatNode.typemax(Int32)guard (clear error pointing atNode).Also adds the reader-orientation table to the README (the four readers behind one accessor set). Targets
v0.5-dev.