fix: certain inputs causing regex matching to hang #3500
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antfu
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antfu
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Jan 17, 2024
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Hi there! I recently discovered an input file that causes UnoCSS to completely hang with 100% CPU usage, and after some investigation it seems to be due to this regex.
You can reproduce the issue by pasting the contents of that input file into https://unocss.dev/play/. The entire tab will freeze.
I went and updated the regexes here to replace all the unbounded
+s and*s with bounded{1,64}s and{0,64}s respectively, and added a test with the problematic input that now completes successfully in under 1s on my machine (previously the test will hang at 100% CPU as well).I chose 64 as the upper bound for all of these expressions for now, since it seems like a safe enough upper limit for the kinds of tokens UnoCSS looks for. Hoping tests will verify whether we need to increase it. Though we could probably drastically improve the worst-case performance of the regex by restricting specific pieces to lower limits. Will leave that to someone who understands the regex better than I do. 🙏