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Re: possible bug in regex and dfa
From: |
arnold |
Subject: |
Re: possible bug in regex and dfa |
Date: |
Sun, 18 Jul 2021 13:30:57 -0600 |
User-agent: |
Heirloom mailx 12.5 7/5/10 |
Hi.
Bruno Haible <bruno@clisp.org> wrote:
> - if REG_NEWLINE is not set, '.' matches newline but '^' does not match
> after the newline.
This is indeed the desired behavior, but regex isn't following it.
REG_NEWLINE being set gets translated into preg->newline_anchor.
Starting at line 620, regexec.c relates to it:
| /* If initial states with non-begbuf contexts have no elements,
| the regex must be anchored. If preg->newline_anchor is set,
| we'll never use init_state_nl, so do not check it. */
| if (dfa->init_state->nodes.nelem == 0
| && dfa->init_state_word->nodes.nelem == 0
| && (dfa->init_state_nl->nodes.nelem == 0
| || !preg->newline_anchor))
| {
| if (start != 0 && last_start != 0)
| return REG_NOMATCH;
| start = last_start = 0;
| }
(As a side note, I don't think the comment matches the code.)
In my case, preg->newline_anchor is zero (correctly), but
dfa->init_state->nodes.nelem is not, so this body isn't executed.
Making the test for preg->newline_anchor the first thing causes my test
case to work correctly but breaks the gawk test suite.
In other words, I think the bug is somewhere in this area, but I
don't understand the regex internals enough to fix it. dfa will also
need looking at.
Thanks,
Arnold