bug#23818: 25.0.95.3: c-beginning-of-defun misbehaviour

[Rolf Ade <rolf@pointsman.de>]

The same in 24.5 and 25.0.95.3:

emacs -Q

Open some random emtpy buffer foo.c, put it in c-mode (M-x c-mode) and
insert the following C code:

#define DBG(x) x

DBG(
static void __dbgAttr () {
    /* something */
}
)

int main (void) 
{
    int i;
    i++;
    i++;
    return i;
}

int foo () 
{
    int i;
    i++;
    i++;
    return 1;
}


Put the point inside function main and C-M-home (or M-x
c-beginning-of-defun). Instead of the beginning of main() the point is
here:

_P_DBG(
...

Far away from

_P_int main(void)
...


This isn't "unbalanced braces in preprocessor statements are
horrendously difficult to parse" as in bug #23775, there are no
unbalanced braces everywhere. It's that some code above the code of a
syntactical correct function disturbs c-beginning-of-defun in finding
the beginning of the function.

Put the point into or at the end of function foo, do C-M-home and you
are at the beginning of function foo. Do C-M-home again, and you are not
at the beginning of main, but of the beginning of DBG.

Remove the DBG(). Now C-M-home works, even if the point is inside or the
end of main().