regcomp.c: fix substring optimizer for ACCEPT inside of CURLY

ACCEPT essentially overrides quantifiers larger than 1. Eg,
/(A){2}/ has a mincount of 2 and a maxcount of 2, and a minlen
of 2 for "AA". But /(A(*ACCEPT)){2}/ should actually have a
mincount of 1, and a minlen of 1 as it can match 'A'. In the regex
engine proper this doesn't matter, we just do the right thing. But
in the optimizer it matters. This patch sets the mincount to 1 in
such cases whenever the contents contains an ACCEPT.

Thanks for Hugo for asking the questions that lead to this patch.

1 files changed, 5 insertions, 0 deletions

diff --git a/regcomp.c b/regcomp.c
index d8bf6876db..a43a6306d7 100644
--- a/regcomp.c
+++ b/regcomp.c
@@ -5681,6 +5681,11 @@ S_study_chunk(pTHX_
                                    : f)
                                   , depth+1, mutate_ok);
 
+                if (data && data->flags & SCF_SEEN_ACCEPT) {
+                    if (mincount > 1)
+                        mincount = 1;
+                }
+
                 if (flags & SCF_DO_STCLASS)
                     data->start_class = oclass;
                 if (mincount == 0 || minnext == 0) {