On Mon, May 12, 2025 at 10:24:12AM -0500, Eric Blake wrote:
> On Mon, May 12, 2025 at 09:54:54AM -0500, Nikolaos Chatzikonstantinou wrote:
> > > $ echo 'eval(1 || (1/0))' | m4-1.4.20
> > > 1
> > > $ echo 'eval(1 || (1/0))' | m4p
> > > m4:stdin:1: divide by zero in eval: 1 || (1/0)
> > > 1
> > >
> >
> > I have a file where I noted some of these here:
> > https://codeberg.org/annoyingusername/m4p/src/branch/main/tests/resources/eval_bugs.txt
>
> Useful. The '1 || (0 / 0)' bug was indeed fixed in 1.4.20. '1 || 2
> &= 3' still complains about invalid operator, but that's intentional:
> &= is not a supported operator. But the complaint about '1 || (2 &=
> 3)') complaining about a missing right parenthesis (instead of a bad
> operator) is something I hadn't noticed before today, and something still
> present in 1.4.20. The parser is correctly detecting that the
> expression is not valid at the point it hits the invalid operator; but
> perhaps the error message could be improved (by stating that it
> expects ')' instead of '&=', for example).
>
> Writing a parser that handles only good expressions is easy. Writing
> a parser that provides sane error messages with useful suggestions
> when the parse fails is hard. Yours may be the first (indirect) bug
> report against 1.4.20!
And here's my first proposed patch for your project:
diff --git i/m4p/m4_eval.py w/m4p/m4_eval.py
index 91f97e7..6f2e565 100644
--- i/m4p/m4_eval.py
+++ w/m4p/m4_eval.py
@@ -168,7 +168,7 @@ calc_grammar = """
| "++" atom -> invalid_unary_operator
| atom "--" -> invalid_unary_operator
| atom "++" -> invalid_unary_operator
- | "(" equation ")"
+ | "(" assignment ")"
%import common.WS_INLINE
so that 'echo "eval((1&3))" | m4p' outputs 1 instead of an error.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc.
Virtualization: qemu.org | libguestfs.org
