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fix ascii class bug and 'Hir::is_match_empty' bug #860

Merged
merged 2 commits into from May 18, 2022
Merged

fix ascii class bug and 'Hir::is_match_empty' bug #860

merged 2 commits into from May 18, 2022

Commits on May 17, 2022

  1. syntax: fix ascii class union bug 

    This fixes a bug in how ASCII class unioning was implemented. Namely, it
previously and erroneously unioned together two classes and then applied
negation/case-folding based on the most recently added class, even if
the class added previously wasn't negated. So for example, given the
regex '[[:alnum:][:^ascii:]]', this would initialize the class with
'[:alnum:]', then add all '[:^ascii:]' codepoints and then negate the
entire thing because of the negation in '[:^ascii:]'. Negating the
entire thing is clearly wrong and not the intended semantics.

We fix this by applying negation/case-folding only to the class we're
dealing with, and then we union it with whatever existing class we're
building.

Fixes #680
    @BurntSushi
    BurntSushi committed May 17, 2022
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  2. syntax: fix 'is_match_empty' predicate 

    This was incorrectly defined for \b. Previously, I had erroneously made
it return true only for \B since \B matches '' and \b does not match
''. However, \b does match the empty string. Like \B, it only matches a
subset of empty strings, depending on what the surrounding context is.
The important bit is that it can match *an* empty string, not that it
matches *the* empty string.

We were not yet using this predicate anywhere in the regex crate, so we
just fix the implementation and update the tests.

This does present a compatibility hazard for anyone who was using this
function, but as of this time, I'm considering this a bug fix since \b
clearly matches an empty string.

Fixes #859
    @BurntSushi
    BurntSushi committed May 17, 2022
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