Commits on Aug 22, 2021

1. Improve f-string expression detection regex so ... …

   we don't accidentally add backslashes to them when normalizing quotes
   because that's invalid syntax!
   
   The problem this commit fixes is that matches would eat too much
   blocking important matches to occur. For example, here's one f-string
   body:
   
       {a}{b}{c}
   
   I know there's no risk of introducing backslashes here, but the regex
   already goes sideways with this. Throwing this example at regex101
   I get:
   
       {a}{b}{c}   # The As and Bs are the two matches, and the upper
       ---- ----   # case letters are the groups with those matches.
       aAaa bbBb
   
   ... we've missed the middle expression (so if any backslashes in a
   more complex example were introduced there we wouldn't bail out
   even though we should -- hence the bug). As it stands the regex
   needs somesort of extra character (or the start/end of the body)
   around the expressions but that isn't always the case as shown
   above.
   
   The fix implemented here is to turn the "eat a surrounding non-curly
   bracket character" groups ie. `(?:[^{]|^)` and `(?:[^}]|$)` into
   negative lookaheads and lookbehinds. This still guarantees the
   already specified rules but without problematically eating extra
   characters ^^

   

   ichard26 committed Aug 22, 2021
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