[PATCH] D50534: [libc++] Fix handling of negated character classes in regex

[Tim Shen via Phabricator via cfe-commits]

timshen added a comment.

I'm not fully equipped with the context right now, but something doesn't add up. if `__neg_chars_.empty()` check is removed, the `(__neg_mask_ == 0)` above should be removed too. They have to be consistent.

However, there is more weirdness in it. The comment above describes the intention:

  union(complement(union(__neg_chars_, __neg_mask_)), other cases...)

With the `__neg_chars_.empty()` and `(__neg_mask_ == 0)` removed, I believe that the code exactly matches the comment. Let's see what happens when users don't specify any negative class or chars. __neg_chars_ and __neg_mask_ will be empty sets, and `union(complement(union(__neg_chars_, __neg_mask_)), other cases...)` always evaluate to true, which means it always matches all characters. This can't be right.

It's likely that the comment description doesn't fully describe the intended behavior. I think we need to figure that out first.


Repository:
  rCXX libc++

https://reviews.llvm.org/D50534