The bind command is broken in 6.1

[Juhász P. <pet...@gm...>]

Hi,

executive summary:
the canonical form of the bind command (e.g. `bind a "replot"`) does
not work, probably since 2024, because of changeset 96d580c508.

explanation:
Gnuplot is one of the few programs I still compile from source,
recompiling rarely, usually only when I change computers or upgrade the
OS. That's why I only noticed now that a company-internal analysis
script that relies heavily on `bind` stopped working after recompiling
the current gnuplot source.

The simplest form of `bind`, e.g. `bind a "replot"`, as given in the
manual, does not do anything, it just fails silently.

I believe the breakage was introduced in commit 96d580c508,
specifically this bit:

@ -1037,8 +1037,7 @@ bind_command()
        char *first = gp_input_line + token[c_token].start_index;
        int size = strcspn(first, " \";");
        lhs = gp_alloc(size + 1, "bind_command->lhs");
-       strncpy(lhs, first, size);
-       lhs[size] = '\0';
+       safe_strncpy(lhs, first, size);
        FPRINTF((stderr,"Got bind unquoted lhs = \"%s\"\n",lhs));
        while (gp_input_line + token[c_token].start_index < first+size)
            c_token++;

`safe_strncpy` is aliased to `strlcpy`, if available, and I seem to
have it, but in any case, this is not an equivalent change.

In the case of a naked single-character first argument to bind, size
will be 1 in the code above. `strlcpy` copies at most `size` (so, 1)
bytes, and sets the last (that is, the only) byte to null.

Then the code that wants to set up the binding receives an empty
string, which causes it to silently fail.

This incorrect behavior can be also seen with the command `bind RR
"replot"`, which is nonsensical and should be an error, but instead it
sets up the binding for "R".

Luckily, the quoted case `bind "R" "replot"` still works.

There may be other instances of this incorrect usage of safe_strncpy, I
haven't checked.

best regards,

Peter Juhasz