https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78276
--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to James K. Lowden from comment #3)
> Here is a nonpathological example taken from a real-world problem were
> std::regex_search fails.
This can be reduced to:
#include <regex>
#include <string>
int main()
{
std::string pattern =
/*1,2*/ "([[:space:]]+(LEADING|TRAILING))?"
"[[:space:]]+" // leading space between pairs
/* 3 */ "("
/* 4,5 */ "\"(" "([\"]{2}|[^\"])*" ")\""
/* 6,7 */ "|" "'(" "([']{2}|[^'])*" ")[']"
/* 8,9 */ "|" "(" "[[:alnum:]]+([_-]+[[:alnum:]]+)*" ")"
/*10,11*/ "|" "==(" "(=?[^=]+)+" ")=="
/* */ ")"
/* */ "[[:space:]]+BY[[:space:]]+"
/* 12 */ "("
/*13,14*/ "(\"" "([\"]{2}|[^\"])*" "\")"
/*15,16*/ "|" "('" "([']{2}|[^'])*" "')"
/*17,18*/ "|" "(" "[[:alnum:]]+([_-]+[[:alnum:]]+)*" ")"
/*19,20*/ "|" "==(" "(=?[^=]+)*" ")=="
/* */ ")"
/* 21 */ "([[:space:]]*[.])?"
;
std::regex re(pattern);
std::string input = R"(
COPY KP003
REPLACING ==+00001== BY +2
== 1 == BY -3 .
PST-TEST-003-1.
MOVE 01 TO REC-CT.
IF WRK-DS-05V00-O005-001 IN GRP-003 (3) EQUAL TO +00009
PERFORM PASS
ELSE
MOVE +009 TO CORRECT-18V0
MOVE WRK-DS-05V00-O005-001 IN
GRP-003 (3) TO COMPUTED-18V0
PERFORM FAIL.
PERFORM PRINT-DETAIL.
ADD +01 TO REC-CT.
IF WRK-DS-09V00-901 EQUAL TO +000000007
PERFORM PASS
ELSE
PERFORM FAIL
MOVE +7 TO CORRECT-18V0
MOVE WRK-DS-09V00-901 TO COMPUTED-18V0.
PERFORM PRINT-DETAIL.
ADD +01 TO REC-CT.
IF WRK-DS-05V00-O005-001 OF GRP-002 (3) EQUAL TO +8
PERFORM PASS
ELSE
MOVE +8 TO CORRECT-18V0
PERFORM FAIL
MOVE WRK-DS-05V00-O005-001 IN GRP-002 (3) TO
COMPUTED-18V0.
PERFORM PRINT-DETAIL.
MOVE 0 TO WRK-DS-09V00-901.
)";
regex_search(input, re);
}
Clang and libc++ give up by throwing std::regex_error(error_complexity):
libc++abi: terminating due to uncaught exception of type std::__1::regex_error:
The complexity of an attempted match against a regular expression exceeded a
pre-set level.
Aborted (core dumped)
So they obviously decided it's better to do that than wait for arbitrarily
complex matches.
