Move has_visited check to the top of the loop in backtrack::Bounded::step #384
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Whoops, was only running a subset of the tests. Fix on the way... |
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Sorry that I haven't had a chance to look at this yet, but I'm skeptical of the approach in this PR. The code that re-implements matching semantics in an ad hoc fashion on the AST seems particularly unfortunate. I haven't given any thought to this, but both RE2 and Go's regexp library have a bitstate backtracker like the one in this crate. Are those regex engines susceptible to this problem? If not, how do they solve it? |
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In particular, I'd like to understand why the |
…step This prevents us from executing instructions if they have been executed before, rather than returning after the instruction has already been executed. Fixes rust-lang#375
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adamcrume
changed the title
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Does this new change look better? It's certainly smaller in scope and size. |
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@adamcrume Yes, much nicer! Thank you for doing this work to fix this subtle bug. It is most appreciated! @bors r+ |
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📌 Commit 6356d1a has been approved by |
Move has_visited check to the top of the loop in backtrack::Bounded::step …pressions With certain repeated empty expressions similar to (x*)*?, the backtracker can go into an infinite loop. This change adds the Progress instruction which requires the engine to make progress to continue matching a repeated subexpression. Fixes #375 Note that this was inspired by https://swtch.com/~rsc/regexp/regexp2.html#real (mentioned in HACKING.md), which mentions that a progress instruction can be used to prevent backtracking loops.
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☀️ Test successful - status-appveyor, status-travis |
…pressions
With certain repeated empty expressions similar to (x*)*?, the backtracker can
go into an infinite loop. This change adds the Progress instruction which
requires the engine to make progress to continue matching a repeated
subexpression.
Fixes #375
Note that this was inspired by https://swtch.com/~rsc/regexp/regexp2.html#real (mentioned in HACKING.md), which mentions that a progress instruction can be used to prevent backtracking loops.