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Trim text around Liquid tags in linear time in liquid-html-parser - #1330
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`value.replace(/\s+$/, '')` retries the match at every position of each whitespace run, so its cost grows with the square of the run length. It was the most expensive single step when parsing Dawn and Horizon. `trimStart()`/`trimEnd()` strip exactly the characters `\s` matches (both use the spec's WhiteSpace and LineTerminator sets), in linear time. A test pins that set and the long-run case.
This was referenced Oct 8, 2026
PhilippeCollin
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October 9, 2026 12:58
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Why
Profiling
toLiquidHtmlASTon Dawn, Horizon and the base theme showed one regular expression taking about 15% of all parse time. It isvalue.replace(/\s+$/, ''), which trims trailing whitespace from text next to Liquid tags.That pattern isn't anchored at the start, so the regex engine tries a match at every position inside each whitespace run, and each attempt reads to the end of the run before failing at
$. A run of k spaces costs about k² steps. Raw-tag bodies such as indented{% schema %}JSON or{% style %}CSS contain many such runs.What
The trimming now uses
trimEnd(), andtrimStart()for the leading side. These strip exactly the characters\smatches, because the spec defines both with the same WhiteSpace and LineTerminator sets, and they run in linear time. A new test pins that character set, including a zero-width space that must be kept. A second test parses text containing a 100,000-space run within 1 s; onmainit takes about 5 s.Benchmarks
Apple M3 Pro, Node 24.15. The input is the parser's 429 fixture files (Dawn, Horizon, base theme; 3.4 MB). Builds ran in alternating processes, 5 rounds × 30 passes. Each value is the median.
main:toLiquidHtmlASTmain:toLiquidASTtoLiquidHtmlASTtoLiquidASTThe relative gain is larger with #1329, because that PR removes most of the tokenizer time that otherwise dominates. A text node with a long whitespace run also stops scaling quadratically: an 80,000-space run takes 3.5 s on
mainand 3 ms with this change.ASTs are unchanged.
liquid-html-parser(including the local fixture oracle suites),prettier-plugin-liquidandtheme-check-commontests pass. A differential run againstmainover about 25,700 inputs (every.liquidfile in the repo, plus random and mutated templates) found 0 differences in tokens or ASTs, positions included.Related: #1329 (tokenizer fast path). Found while profiling after it.