automata: fix bug where reverse NFA lacked an unanchored prefix #1170
+85
−4
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Previously, when compiling a Thompson NFA, we were omitting an
unanchored prefix when the HIR contained a
^
in its prefix. We didthis because unanchored prefix in that case would never match because of
the requirement imposed by
^
.The problem with that is it's incorrect when compiling a reverse
automaton. For example, in the case of building a reverse NFA for
^Qu
,we should sitll include an unanchored prefix because the
^
in thatcase has no conflict with it. It would be like if we omitted an
unanchored prefix for
Qu$
in a forward NFA, which is obviously wrong.The fix here is pretty simple: in the reverse case, check for
$
in thesuffix of the HIR rather than a
^
in the prefix.Fixes #1169