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Disallow quantification of assertion conditions, for Perl compatibility (and in 

any case it didn't always work).
This commit is contained in:
Philip.Hazel 2015-01-28 17:31:11 +00:00
parent 6c8945b8d8
commit 0011aaa712
8 changed files with 117 additions and 53 deletions
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11
ChangeLog
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@ -44,6 +44,17 @@ to be incorrectly calculated, leading to overwriting.
segfault at compile time (while trying to find the minimum matching length). segfault at compile time (while trying to find the minimum matching length).
The infinite loop is now broken (with the minimum length unset, that is, zero). The infinite loop is now broken (with the minimum length unset, that is, zero).
9. If an assertion that was used as a condition was quantified with a minimum
of zero, matching went wrong. In particular, if the whole group had unlimited
repetition and could match an empty string, a segfault was likely. The pattern
(?(?=0)?)+ is an example that caused this. Perl allows assertions to be
quantified, but not if they are being used as conditions, so the above pattern
is faulted by Perl. PCRE2 has now been changed so that it also rejects such
patterns.
10. The error message for an invalid quantifier has been changed from "nothing
to repeat" to "quantifier does not follow a repeatable item".
Version 10.00 05-January-2015 Version 10.00 05-January-2015
----------------------------- -----------------------------

15
doc/pcre2pattern.3
View File

@ -1,4 +1,4 @@
.TH PCRE2PATTERN 3 "26 January 2015" "PCRE2 10.00" .TH PCRE2PATTERN 3 "28 January 2015" "PCRE2 10.00"
.SH NAME .SH NAME
PCRE2 - Perl-compatible regular expressions (revised API) PCRE2 - Perl-compatible regular expressions (revised API)
.SH "PCRE2 REGULAR EXPRESSION DETAILS" .SH "PCRE2 REGULAR EXPRESSION DETAILS"
@ -1742,8 +1742,8 @@ items:
the \eR escape sequence the \eR escape sequence
an escape such as \ed or \epL that matches a single character an escape such as \ed or \epL that matches a single character
a character class a character class
a back reference (see next section) a back reference
a parenthesized subpattern (including assertions) a parenthesized subpattern (including most assertions)
a subroutine call to a subpattern (recursive or otherwise) a subroutine call to a subpattern (recursive or otherwise)
.sp .sp
The general repetition quantifier specifies a minimum and maximum number of The general repetition quantifier specifies a minimum and maximum number of
@ -2152,10 +2152,11 @@ numbering the capturing subpatterns in the whole pattern. However, substring
capturing is carried out only for positive assertions. (Perl sometimes, but not capturing is carried out only for positive assertions. (Perl sometimes, but not
always, does do capturing in negative assertions.) always, does do capturing in negative assertions.)
.P .P
For compatibility with Perl, assertion subpatterns may be repeated; though For compatibility with Perl, most assertion subpatterns may be repeated; though
it makes no sense to assert the same thing several times, the side effect of it makes no sense to assert the same thing several times, the side effect of
capturing parentheses may occasionally be useful. In practice, there only three capturing parentheses may occasionally be useful. However, an assertion that
cases: forms the condition for a conditional subpattern may not be quantified. In
practice, for other assertions, there only three cases:
.sp .sp
(1) If the quantifier is {0}, the assertion is never obeyed during matching. (1) If the quantifier is {0}, the assertion is never obeyed during matching.
However, it may contain internal capturing parenthesized groups that are called However, it may contain internal capturing parenthesized groups that are called
@ -3301,6 +3302,6 @@ Cambridge, England.
.rs .rs
.sp .sp
.nf .nf
Last updated: 26 January 2015 Last updated: 28 January 2015
Copyright (c) 1997-2015 University of Cambridge. Copyright (c) 1997-2015 University of Cambridge.
.fi .fi

33
src/pcre2_compile.c
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@ -5178,14 +5178,19 @@ for (;; ptr++)
} }
/* For conditions that are assertions, check the syntax, and then exit /* For conditions that are assertions, check the syntax, and then exit
the switch. This will take control down to where bracketed groups, the switch. This will take control down to where bracketed groups
including assertions, are processed. */ are processed. The assertion will be handled as part of the group,
but we need to identify this case because the conditional assertion may
not be quantifier. */
if (tempptr[1] == CHAR_QUESTION_MARK && if (tempptr[1] == CHAR_QUESTION_MARK &&
(tempptr[2] == CHAR_EQUALS_SIGN || (tempptr[2] == CHAR_EQUALS_SIGN ||
tempptr[2] == CHAR_EXCLAMATION_MARK || tempptr[2] == CHAR_EXCLAMATION_MARK ||
tempptr[2] == CHAR_LESS_THAN_SIGN)) tempptr[2] == CHAR_LESS_THAN_SIGN))
{
cb->iscondassert = TRUE;
break; break;
}
/* Other conditions use OP_CREF/OP_DNCREF/OP_RREF/OP_DNRREF, and all /* Other conditions use OP_CREF/OP_DNCREF/OP_RREF/OP_DNRREF, and all
need to skip at least 1+IMM2_SIZE bytes at the start of the group. */ need to skip at least 1+IMM2_SIZE bytes at the start of the group. */
@ -6098,12 +6103,22 @@ for (;; ptr++)
goto FAILED; goto FAILED;
} }
/* Assertions used not to be repeatable, but this was changed for Perl /* All assertions used not to be repeatable, but this was changed for Perl
compatibility, so all kinds can now be repeated. We copy code into a compatibility. All kinds can now be repeated except for assertions that are
conditions (Perl also forbids these to be repeated). We copy code into a
non-register variable (tempcode) in order to be able to pass its address non-register variable (tempcode) in order to be able to pass its address
because some compilers complain otherwise. */ because some compilers complain otherwise. At the start of a conditional
group whose condition is an assertion, cb->iscondassert is set. We unset it
here so as to allow assertions later in the group to be quantified. */
if (bravalue >= OP_ASSERT && bravalue <= OP_ASSERTBACK_NOT &&
cb->iscondassert)
{
previous = NULL;
cb->iscondassert = FALSE;
}
else previous = code;
previous = code; /* For handling repetition */
*code = bravalue; *code = bravalue;
tempcode = code; tempcode = code;
tempreqvary = cb->req_varyopt; /* Save value before bracket */ tempreqvary = cb->req_varyopt; /* Save value before bracket */
@ -6121,9 +6136,9 @@ for (;; ptr++)
skipbytes, /* Skip over bracket number */ skipbytes, /* Skip over bracket number */
cond_depth + cond_depth +
((bravalue == OP_COND)?1:0), /* Depth of condition subpatterns */ ((bravalue == OP_COND)?1:0), /* Depth of condition subpatterns */
&subfirstcu, /* For possible first char */ &subfirstcu, /* For possible first char */
&subfirstcuflags, &subfirstcuflags,
&subreqcu, /* For possible last char */ &subreqcu, /* For possible last char */
&subreqcuflags, &subreqcuflags,
bcptr, /* Current branch chain */ bcptr, /* Current branch chain */
cb, /* Compile data block */ cb, /* Compile data block */
@ -7474,6 +7489,7 @@ cb.end_pattern = pattern + patlen;
cb.external_flags = 0; cb.external_flags = 0;
cb.external_options = options; cb.external_options = options;
cb.hwm = cworkspace; cb.hwm = cworkspace;
cb.iscondassert = FALSE;
cb.max_lookbehind = 0; cb.max_lookbehind = 0;
cb.name_entry_size = 0; cb.name_entry_size = 0;
cb.name_table = NULL; cb.name_table = NULL;
@ -7725,6 +7741,7 @@ cb.max_lookbehind = 0;
cb.name_table = (PCRE2_UCHAR *)((uint8_t *)re + sizeof(pcre2_real_code)); cb.name_table = (PCRE2_UCHAR *)((uint8_t *)re + sizeof(pcre2_real_code));
cb.start_code = codestart; cb.start_code = codestart;
cb.hwm = (PCRE2_UCHAR *)(cb.start_workspace); cb.hwm = (PCRE2_UCHAR *)(cb.start_workspace);
cb.iscondassert = FALSE;
cb.req_varyopt = 0; cb.req_varyopt = 0;
cb.had_accept = FALSE; cb.had_accept = FALSE;
cb.had_pruneorskip = FALSE; cb.had_pruneorskip = FALSE;

2
src/pcre2_error.c
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@ -74,7 +74,7 @@ static const char compile_error_texts[] =
"missing terminating ] for character class\0" "missing terminating ] for character class\0"
"invalid escape sequence in character class\0" "invalid escape sequence in character class\0"
"range out of order in character class\0" "range out of order in character class\0"
"nothing to repeat\0" "quantifier does not follow a repeatable item\0"
/* 10 */ /* 10 */
"internal error: unexpected repeat\0" "internal error: unexpected repeat\0"
"unrecognized character after (? or (?-\0" "unrecognized character after (? or (?-\0"

1
src/pcre2_intmodedep.h
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@ -688,6 +688,7 @@ typedef struct compile_block {
BOOL had_pruneorskip; /* (*PRUNE) or (*SKIP) encountered */ BOOL had_pruneorskip; /* (*PRUNE) or (*SKIP) encountered */
BOOL check_lookbehind; /* Lookbehinds need later checking */ BOOL check_lookbehind; /* Lookbehinds need later checking */
BOOL dupnames; /* Duplicate names exist */ BOOL dupnames; /* Duplicate names exist */
BOOL iscondassert; /* Next assert is a condition */
} compile_block; } compile_block;
/* Structure for keeping the properties of the in-memory stack used /* Structure for keeping the properties of the in-memory stack used

40
src/pcre2_match.c
View File

@ -75,7 +75,7 @@ implementing this. */
#define OVFLMASK 0xffff0000 /* The bits used for the overflow flag */ #define OVFLMASK 0xffff0000 /* The bits used for the overflow flag */
#define OVFLBIT 0x00010000 /* The bit that is set for overflow */ #define OVFLBIT 0x00010000 /* The bit that is set for overflow */
/* Values for setting in mb->match_function_type to indicate two special types /* Bits for setting in mb->match_function_type to indicate two special types
of call to match(). We do it this way to save on using another stack variable, of call to match(). We do it this way to save on using another stack variable,
as stack usage is to be discouraged. */ as stack usage is to be discouraged. */
@ -487,7 +487,7 @@ data and the last captured value. */
do do
{ {
if (cbegroup) mb->match_function_type = MATCH_CBEGROUP; if (cbegroup) mb->match_function_type |= MATCH_CBEGROUP;
rrc = match(eptr, callpat + PRIV(OP_lengths)[*callpat], mstart, offset_top, rrc = match(eptr, callpat + PRIV(OP_lengths)[*callpat], mstart, offset_top,
mb, eptrb, rdepth + 1); mb, eptrb, rdepth + 1);
memcpy(mb->ovector, new_recursive->ovec_save, memcpy(mb->ovector, new_recursive->ovec_save,
@ -771,9 +771,9 @@ if (mb->match_call_count++ >= mb->match_limit) RRETURN(PCRE2_ERROR_MATCHLIMIT);
if (rdepth >= mb->match_limit_recursion) RRETURN(PCRE2_ERROR_RECURSIONLIMIT); if (rdepth >= mb->match_limit_recursion) RRETURN(PCRE2_ERROR_RECURSIONLIMIT);
/* At the start of a group with an unlimited repeat that may match an empty /* At the start of a group with an unlimited repeat that may match an empty
string, the variable mb->match_function_type is set to MATCH_CBEGROUP. It is string, the variable mb->match_function_type contains the MATCH_CBEGROUP bit.
done this way to save having to use another function argument, which would take It is done this way to save having to use another function argument, which
up space on the stack. See also MATCH_CONDASSERT below. would take up space on the stack. See also MATCH_CONDASSERT below.
When MATCH_CBEGROUP is set, add the current subject pointer to the chain of When MATCH_CBEGROUP is set, add the current subject pointer to the chain of
such remembered pointers, to be checked when we hit the closing ket, in order such remembered pointers, to be checked when we hit the closing ket, in order
@ -782,12 +782,12 @@ other circumstances, don't add to the chain. The MATCH_CBEGROUP feature must
NOT be used with tail recursion, because the memory block that is used is on NOT be used with tail recursion, because the memory block that is used is on
the stack, so a new one may be required for each match(). */ the stack, so a new one may be required for each match(). */
if (mb->match_function_type == MATCH_CBEGROUP) if ((mb->match_function_type & MATCH_CBEGROUP) != 0)
{ {
newptrb.epb_saved_eptr = eptr; newptrb.epb_saved_eptr = eptr;
newptrb.epb_prev = eptrb; newptrb.epb_prev = eptrb;
eptrb = &newptrb; eptrb = &newptrb;
mb->match_function_type = 0; mb->match_function_type &= ~MATCH_CBEGROUP;
} }
/* Now, at last, we can start processing the opcodes. */ /* Now, at last, we can start processing the opcodes. */
@ -1016,7 +1016,7 @@ for (;;)
for (;;) for (;;)
{ {
if (op >= OP_SBRA) mb->match_function_type = MATCH_CBEGROUP; if (op >= OP_SBRA) mb->match_function_type |= MATCH_CBEGROUP;
RMATCH(eptr, ecode + PRIV(OP_lengths)[*ecode], offset_top, mb, RMATCH(eptr, ecode + PRIV(OP_lengths)[*ecode], offset_top, mb,
eptrb, RM1); eptrb, RM1);
if (rrc == MATCH_ONCE) break; /* Backing up through an atomic group */ if (rrc == MATCH_ONCE) break; /* Backing up through an atomic group */
@ -1091,7 +1091,7 @@ for (;;)
for (;;) for (;;)
{ {
if (op >= OP_SBRA || op == OP_ONCE) if (op >= OP_SBRA || op == OP_ONCE)
mb->match_function_type = MATCH_CBEGROUP; mb->match_function_type |= MATCH_CBEGROUP;
/* If this is not a possibly empty group, and there are no (*THEN)s in /* If this is not a possibly empty group, and there are no (*THEN)s in
the pattern, and this is the final alternative, optimize as described the pattern, and this is the final alternative, optimize as described
@ -1181,7 +1181,7 @@ for (;;)
for (;;) for (;;)
{ {
mb->ovector[mb->offset_end - number] = eptr - mb->start_subject; mb->ovector[mb->offset_end - number] = eptr - mb->start_subject;
if (op >= OP_SBRA) mb->match_function_type = MATCH_CBEGROUP; if (op >= OP_SBRA) mb->match_function_type |= MATCH_CBEGROUP;
RMATCH(eptr, ecode + PRIV(OP_lengths)[*ecode], offset_top, mb, RMATCH(eptr, ecode + PRIV(OP_lengths)[*ecode], offset_top, mb,
eptrb, RM63); eptrb, RM63);
if (rrc == MATCH_KETRPOS) if (rrc == MATCH_KETRPOS)
@ -1255,7 +1255,7 @@ for (;;)
for (;;) for (;;)
{ {
if (op >= OP_SBRA) mb->match_function_type = MATCH_CBEGROUP; if (op >= OP_SBRA) mb->match_function_type |= MATCH_CBEGROUP;
RMATCH(eptr, ecode + PRIV(OP_lengths)[*ecode], offset_top, mb, RMATCH(eptr, ecode + PRIV(OP_lengths)[*ecode], offset_top, mb,
eptrb, RM48); eptrb, RM48);
if (rrc == MATCH_KETRPOS) if (rrc == MATCH_KETRPOS)
@ -1404,11 +1404,11 @@ for (;;)
break; break;
/* The condition is an assertion. Call match() to evaluate it - setting /* The condition is an assertion. Call match() to evaluate it - setting
mb->match_function_type to MATCH_CONDASSERT causes it to stop at the end the MATCH_CONDASSERT bit in mb->match_function_type causes it to stop at
of an assertion. */ the end of an assertion. */
default: default:
mb->match_function_type = MATCH_CONDASSERT; mb->match_function_type |= MATCH_CONDASSERT;
RMATCH(eptr, ecode, offset_top, mb, NULL, RM3); RMATCH(eptr, ecode, offset_top, mb, NULL, RM3);
if (rrc == MATCH_MATCH) if (rrc == MATCH_MATCH)
{ {
@ -1459,7 +1459,7 @@ for (;;)
goto TAIL_RECURSE; goto TAIL_RECURSE;
} }
mb->match_function_type = MATCH_CBEGROUP; mb->match_function_type |= MATCH_CBEGROUP;
RMATCH(eptr, ecode, offset_top, mb, eptrb, RM49); RMATCH(eptr, ecode, offset_top, mb, eptrb, RM49);
RRETURN(rrc); RRETURN(rrc);
} }
@ -1548,10 +1548,10 @@ for (;;)
case OP_ASSERT: case OP_ASSERT:
case OP_ASSERTBACK: case OP_ASSERTBACK:
save_mark = mb->mark; save_mark = mb->mark;
if (mb->match_function_type == MATCH_CONDASSERT) if ((mb->match_function_type & MATCH_CONDASSERT) != 0)
{ {
condassert = TRUE; condassert = TRUE;
mb->match_function_type = 0; mb->match_function_type &= ~MATCH_CONDASSERT;
} }
else condassert = FALSE; else condassert = FALSE;
@ -1619,10 +1619,10 @@ for (;;)
case OP_ASSERT_NOT: case OP_ASSERT_NOT:
case OP_ASSERTBACK_NOT: case OP_ASSERTBACK_NOT:
save_mark = mb->mark; save_mark = mb->mark;
if (mb->match_function_type == MATCH_CONDASSERT) if ((mb->match_function_type & MATCH_CONDASSERT) != 0)
{ {
condassert = TRUE; condassert = TRUE;
mb->match_function_type = 0; mb->match_function_type &= ~MATCH_CONDASSERT;
} }
else condassert = FALSE; else condassert = FALSE;
@ -1844,7 +1844,7 @@ for (;;)
cbegroup = (*callpat >= OP_SBRA); cbegroup = (*callpat >= OP_SBRA);
do do
{ {
if (cbegroup) mb->match_function_type = MATCH_CBEGROUP; if (cbegroup) mb->match_function_type |= MATCH_CBEGROUP;
RMATCH(eptr, callpat + PRIV(OP_lengths)[*callpat], offset_top, RMATCH(eptr, callpat + PRIV(OP_lengths)[*callpat], offset_top,
mb, eptrb, RM6); mb, eptrb, RM6);
memcpy(mb->ovector, new_recursive.ovec_save, memcpy(mb->ovector, new_recursive.ovec_save,

18
testdata/testinput2 vendored
View File

@ -4078,10 +4078,10 @@ a random value. /Ix
# End of substitute tests # End of substitute tests
"((?=(?(?=(?(?=(?(?=())))*)))))" "((?=(?(?=(?(?=(?(?=()))))))))"
a a
"(?(?=)?==)(((((((((?=)))))))))" "(?(?=)==)(((((((((?=)))))))))"
a a
/(a)(b)|(c)/ /(a)(b)|(c)/
@ -4138,4 +4138,18 @@ a random value. /Ix
/(?<N>(?J)(?<N>))(?-J)\k<N>/ /(?<N>(?J)(?<N>))(?-J)\k<N>/
# Quantifiers are not allowed on condition assertions, but are otherwise
# OK in conditions.
/(?(?=0)?)+/
/(?(?=0)(?=00)?00765)/
00765
/(?(?=0)(?=00)?00765|(?!3).56)/
00765
456
** Failers
356
# End of testinput2 # End of testinput2

50
testdata/testoutput2 vendored
View File

@ -147,7 +147,7 @@ Failed: error 107 at offset 2: invalid escape sequence in character class
Failed: error 108 at offset 3: range out of order in character class Failed: error 108 at offset 3: range out of order in character class
/^*/ /^*/
Failed: error 109 at offset 1: nothing to repeat Failed: error 109 at offset 1: quantifier does not follow a repeatable item
/(abc/ /(abc/
Failed: error 114 at offset 4: missing closing parenthesis Failed: error 114 at offset 4: missing closing parenthesis
@ -230,7 +230,7 @@ Subject length lower bound = 1
Failed: error 115 at offset 6: reference to non-existent subpattern Failed: error 115 at offset 6: reference to non-existent subpattern
/{4,5}abc/ /{4,5}abc/
Failed: error 109 at offset 4: nothing to repeat Failed: error 109 at offset 4: quantifier does not follow a repeatable item
/(a)(b)(c)\2/I /(a)(b)(c)\2/I
Capturing subpattern count = 3 Capturing subpattern count = 3
@ -883,10 +883,10 @@ Failed: error 106 at offset 4: missing terminating ] for character class
Failed: error 106 at offset 2: missing terminating ] for character class Failed: error 106 at offset 2: missing terminating ] for character class
/*a/ /*a/
Failed: error 109 at offset 0: nothing to repeat Failed: error 109 at offset 0: quantifier does not follow a repeatable item
/(*)b/ /(*)b/
Failed: error 109 at offset 1: nothing to repeat Failed: error 109 at offset 1: quantifier does not follow a repeatable item
/abc)/ /abc)/
Failed: error 122 at offset 3: unmatched closing parenthesis Failed: error 122 at offset 3: unmatched closing parenthesis
@ -895,7 +895,7 @@ Failed: error 122 at offset 3: unmatched closing parenthesis
Failed: error 114 at offset 4: missing closing parenthesis Failed: error 114 at offset 4: missing closing parenthesis
/a**/ /a**/
Failed: error 109 at offset 2: nothing to repeat Failed: error 109 at offset 2: quantifier does not follow a repeatable item
/)(/ /)(/
Failed: error 122 at offset 0: unmatched closing parenthesis Failed: error 122 at offset 0: unmatched closing parenthesis
@ -919,10 +919,10 @@ Failed: error 106 at offset 4: missing terminating ] for character class
Failed: error 106 at offset 2: missing terminating ] for character class Failed: error 106 at offset 2: missing terminating ] for character class
/*a/Ii /*a/Ii
Failed: error 109 at offset 0: nothing to repeat Failed: error 109 at offset 0: quantifier does not follow a repeatable item
/(*)b/Ii /(*)b/Ii
Failed: error 109 at offset 1: nothing to repeat Failed: error 109 at offset 1: quantifier does not follow a repeatable item
/abc)/Ii /abc)/Ii
Failed: error 122 at offset 3: unmatched closing parenthesis Failed: error 122 at offset 3: unmatched closing parenthesis
@ -931,7 +931,7 @@ Failed: error 122 at offset 3: unmatched closing parenthesis
Failed: error 114 at offset 4: missing closing parenthesis Failed: error 114 at offset 4: missing closing parenthesis
/a**/Ii /a**/Ii
Failed: error 109 at offset 2: nothing to repeat Failed: error 109 at offset 2: quantifier does not follow a repeatable item
/)(/Ii /)(/Ii
Failed: error 122 at offset 0: unmatched closing parenthesis Failed: error 122 at offset 0: unmatched closing parenthesis
@ -3025,16 +3025,16 @@ Last code unit = 'c'
Subject length lower bound = 3 Subject length lower bound = 3
/a+?+/I /a+?+/I
Failed: error 109 at offset 3: nothing to repeat Failed: error 109 at offset 3: quantifier does not follow a repeatable item
/a{2,3}?+b/I /a{2,3}?+b/I
Failed: error 109 at offset 7: nothing to repeat Failed: error 109 at offset 7: quantifier does not follow a repeatable item
/(?U)a+?+/I /(?U)a+?+/I
Failed: error 109 at offset 7: nothing to repeat Failed: error 109 at offset 7: quantifier does not follow a repeatable item
/a{2,3}?+b/I,ungreedy /a{2,3}?+b/I,ungreedy
Failed: error 109 at offset 7: nothing to repeat Failed: error 109 at offset 7: quantifier does not follow a repeatable item
/x(?U)a++b/IB /x(?U)a++b/IB
------------------------------------------------------------------ ------------------------------------------------------------------
@ -8816,7 +8816,7 @@ No match
0: a 0: a
/a(*FAIL)+b/ /a(*FAIL)+b/
Failed: error 109 at offset 8: nothing to repeat Failed: error 109 at offset 8: quantifier does not follow a repeatable item
/(abc|pqr|123){0}[xyz]/I /(abc|pqr|123){0}[xyz]/I
Capturing subpattern count = 1 Capturing subpattern count = 1
@ -13724,13 +13724,13 @@ Failed: error -34: bad option value
# End of substitute tests # End of substitute tests
"((?=(?(?=(?(?=(?(?=())))*)))))" "((?=(?(?=(?(?=(?(?=()))))))))"
a a
0: 0:
1: 1:
2: 2:
"(?(?=)?==)(((((((((?=)))))))))" "(?(?=)==)(((((((((?=)))))))))"
a a
No match No match
@ -13897,4 +13897,24 @@ Matched, but too many substrings
/(?<N>(?J)(?<N>))(?-J)\k<N>/ /(?<N>(?J)(?<N>))(?-J)\k<N>/
# Quantifiers are not allowed on condition assertions, but are otherwise
# OK in conditions.
/(?(?=0)?)+/
Failed: error 109 at offset 7: quantifier does not follow a repeatable item
/(?(?=0)(?=00)?00765)/
00765
0: 00765
/(?(?=0)(?=00)?00765|(?!3).56)/
00765
0: 00765
456
0: 456
** Failers
No match
356
No match
# End of testinput2 # End of testinput2