From: s.wanabe@... Date: 2021-05-01T11:06:59+00:00 Subject: [ruby-core:103681] [Ruby master Bug#17774] Quantified empty group causes regex to fail Issue #17774 has been updated by wanabe (_ wanabe). The reproduction example could be a bit shorter. ``` $ ruby -ve 'p "xxxx" =~ /(?:x(){5})*$/, "xxxx" =~ /(?:x(){4})*$/' ruby 3.1.0dev (2021-05-01T02:04:17Z origin/master 121fa24a34) [x86_64-linux] 3 0 ``` This problem has already been fixed in Oniguruma, a derivative of Onigmo. https://github.com/kkos/oniguruma/commit/ca64663ca8bb34ca7dc219d18ec6e475cca9dec8 ``` $ (git checkout ca64663ca8bb34ca7dc219d18ec6e475cca9dec8~ && autoreconf -vfi && ./configure && make -j6 && sed -i sample/simple.c -e 's/\(pattern *= [^"]*\)"[^"]*"/\1"(?:x(){5})*$"/' -e 's/\(str *= [^"]*\)"[^"]*"/\1"xxxx"/' && (cd sample; make simple)) > build.log 2>&1 && ./sample/simple match at 3 0: (3-4) 1: (4-4) $ (git checkout ca64663ca8bb34ca7dc219d18ec6e475cca9dec8 && autoreconf -vfi && ./configure && make -j6 && sed -i sample/simple.c -e 's/\(pattern *= [^"]*\)"[^"]*"/\1"(?:x(){5})*$"/' -e 's/\(str *= [^"]*\)"[^"]*"/\1"xxxx"/' && (cd sample; make simple)) > build.log 2>&1 && ./sample/simple match at 0 0: (0-4) 1: (4-4) ``` I think that introducing a mechanism that exists in Oniguruma 6.x, such as empty_status_mem and set_empty_status_check_trav, may solve the problem. ---------------------------------------- Bug #17774: Quantified empty group causes regex to fail https://bugs.ruby-lang.org/issues/17774#change-91776 * Author: Davidebyzero (David Ellsworth) * Status: Open * Priority: Normal * ruby -v: ruby 2.7.2p137 (2020-10-01 revision 5445e04352) [x86_64-msys] * Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN ---------------------------------------- The regex `^((x*)(?=\2$))*x$` matches powers of 2 in unary, expressed as strings of `x` characters whose length is the number. Adding an empty group `()` in the middle of it should have no effect on its operation, and indeed it does not. `^((x*)()(?=\2$))*x$` still matches powers of 2 just fine. Quantifying that empty group, `(){4}`, should still have no effect. And indeed, `^((x*)(){4}(?=\2$))*x$` still matches powers of 2. But quantify that to `(){5}`, and suddenly it fails. The following command line should print `1`, but instead prints nothing: ``` ruby -e 'print 1 if "x"*32 =~ /^((x*)(){5}(?=\2$))*x$/' ``` However this one does print `1`: ``` ruby -e 'print 1 if "x"*32 =~ /^((x*)(){4}(?=\2$))*x$/' ``` Bug found to occur on [Try It Online](https://tio.run/): `ruby 2.5.5p157 (2019-03-15 revision 67260) [x86_64-linux]` Bug confirmed to happen on my own machine: `ruby 2.7.2p137 (2020-10-01 revision 5445e04352) [x86_64-msys]` Solving the challenge [Is that number a Two Bit Number������?](https://codegolf.stackexchange.com/questions/211840/is-that-number-a-two-bit-number%ef%b8%8f/222792#222792) on Code Golf Stack Exchange is what led me to discover this bug. -- https://bugs.ruby-lang.org/ Unsubscribe: