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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


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.



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