From 071146184a59de4ac20f5508903fdbc21f963b6c Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Tue, 24 Aug 2021 16:37:27 -0400 Subject: [PATCH] Fix regexp misbehavior with capturing parens inside "{0}". Regexps like "(.){0}...\1" drew an "invalid backreference number". That's not unreasonable on its face, since the capture group will never be matched if it's iterated zero times. However, other engines such as Perl's don't complain about this, nor do we throw an error for related cases such as "(.)|\1", even though that backref can never succeed either. Also, if the zero-iterations case happens at runtime rather than compile time --- say, "(x)*...\1" when there's no "x" to be found --- that's not an error, we just deem the backref to not match. Making this even less defensible, no error was thrown for nested cases such as "((.)){0}...\2"; and to add insult to injury, those cases could result in assertion failures instead. (It seems that nothing especially bad happened in non-assert builds, though.) Let's just fix it so that no error is thrown and instead the backref is deemed to never match, so that compile-time detection of no iterations behaves the same as run-time detection. Per report from Mark Dilger. This appears to be an aboriginal error in Spencer's library, so back-patch to all supported versions. Pre-v14, it turns out to also be necessary to back-patch one aspect of commits cb76fbd7e/00116dee5, namely to create capture-node subREs with the begin/end states of their subexpressions, not the current lp/rp of the outer parseqatom invocation. Otherwise delsub complains that we're trying to disconnect a state from itself. This is a bit scary but code examination shows that it's safe: in the pre-v14 code, if we want to wrap iteration around the subexpression, the first thing we do is overwrite the atom's begin/end fields with new states. So the bogus values didn't survive long enough to be used for anything, except if no iteration is required, in which case it doesn't matter. Discussion: https://postgr.es/m/A099E4A8-4377-4C64-A98C-3DEDDC075502@enterprisedb.com --- src/backend/regex/regcomp.c | 24 ++++++++++++++++++------ src/test/regress/expected/regex.out | 19 +++++++++++++++++++ src/test/regress/sql/regex.sql | 5 +++++ 3 files changed, 42 insertions(+), 6 deletions(-) diff --git a/src/backend/regex/regcomp.c b/src/backend/regex/regcomp.c index 91078dcd80..fba44625d7 100644 --- a/src/backend/regex/regcomp.c +++ b/src/backend/regex/regcomp.c @@ -958,7 +958,7 @@ parseqatom(struct vars *v, if (cap) { v->subs[subno] = atom; - t = subre(v, '(', atom->flags | CAP, lp, rp); + t = subre(v, '(', atom->flags | CAP, s, s2); NOERR(); t->subno = subno; t->left = atom; @@ -1041,11 +1041,23 @@ parseqatom(struct vars *v, /* annoying special case: {0} or {0,0} cancels everything */ if (m == 0 && n == 0) { - if (atom != NULL) - freesubre(v, atom); - if (atomtype == '(') - v->subs[subno] = NULL; - delsub(v->nfa, lp, rp); + /* + * If we had capturing subexpression(s) within the atom, we don't want + * to destroy them, because it's legal (if useless) to back-ref them + * later. Hence, just unlink the atom from lp/rp and then ignore it. + */ + if (atom != NULL && (atom->flags & CAP)) + { + delsub(v->nfa, lp, atom->begin); + delsub(v->nfa, atom->end, rp); + } + else + { + /* Otherwise, we can clean up any subre infrastructure we made */ + if (atom != NULL) + freesubre(v, atom); + delsub(v->nfa, lp, rp); + } EMPTYARC(lp, rp); return; } diff --git a/src/test/regress/expected/regex.out b/src/test/regress/expected/regex.out index fccd91566c..f842d5724c 100644 --- a/src/test/regress/expected/regex.out +++ b/src/test/regress/expected/regex.out @@ -567,6 +567,25 @@ select 'a' ~ '()+\1'; t (1 row) +-- Test incorrect removal of capture groups within {0} +select 'xxx' ~ '(.){0}(\1)' as f; + f +--- + f +(1 row) + +select 'xxx' ~ '((.)){0}(\2)' as f; + f +--- + f +(1 row) + +select 'xyz' ~ '((.)){0}(\2){0}' as t; + t +--- + t +(1 row) + -- Test ancient oversight in when to apply zaptreesubs select 'abcdef' ~ '^(.)\1|\1.' as f; f diff --git a/src/test/regress/sql/regex.sql b/src/test/regress/sql/regex.sql index 762b3ae69b..758de44d2f 100644 --- a/src/test/regress/sql/regex.sql +++ b/src/test/regress/sql/regex.sql @@ -135,6 +135,11 @@ select 'a' ~ '.. ()|\1'; select 'a' ~ '()*\1'; select 'a' ~ '()+\1'; +-- Test incorrect removal of capture groups within {0} +select 'xxx' ~ '(.){0}(\1)' as f; +select 'xxx' ~ '((.)){0}(\2)' as f; +select 'xyz' ~ '((.)){0}(\2){0}' as t; + -- Test ancient oversight in when to apply zaptreesubs select 'abcdef' ~ '^(.)\1|\1.' as f; select 'abadef' ~ '^((.)\2|..)\2' as f;