perf(source-map): lazy-build lineStarts in parseMdWithSourceMap - #109
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computeLineStarts(md) was eagerly called on every parseMdWithSourceMap() invocation, but getRaw() never uses it. Defer to first use in getSourceRange() / getFieldSourceRange() via nullish coalescing assignment. For getRaw()-only callers this skips the full Markdown scan and number[] allocation entirely.
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What
Defer
computeLineStarts(md)inparseMdWithSourceMap()from eager to lazy initialization via??=.Why
getRaw()never useslineStarts, but everyparseMdWithSourceMap()call currently scans the full Markdown source to build anumber[]line index. ForgetRaw()-only callers this array is pure waste — onenumberper line of input, allocated and immediately GC'd.A 256 KiB Markdown file with ~4000 lines allocates a
number[]of 4000+ entries (32 KiB+) that is never read.Changes
const lineStarts = computeLineStarts(md)withlet lineStarts: number[] | undefined.lineStarts ??= computeLineStarts(md)at the top ofgetSourceRange()andgetFieldSourceRange()— the only two call sites that need it.Impact
getRaw()-only callers, skips thenumber[]allocation entirely (saves ~1 entry per line of input).Verification