bug#39373: 27.0.50; [PATCH] mode-local-print-bindings broken with lexical-binding

[Mattias Engdegård]

31 jan. 2020 kl. 21.25 skrev Eli Zaretskii <eliz@gnu.org>:

> That's not the "usual" way of fixing problems with lexical-binding,
> and it isn't immediately clear to me why that fixes the problem.

'add-to-list' doesn't work on lexical variables because it's a plain function 
taking the variable symbol as argument. 'push' works on lexical variables since 
it is a macro that expands to direct variable reference and setq. I should 
perhaps have included this in the commit message.

Happily, Emacs provides generalised variable support for 'if' and 'cons', so 
that they can be used as target for 'push'.

We could sink the pushes to the leaves of the condition tree, if you prefer:

(cond ((get s 'mode-variable-flag)
       (if (get s 'constant-flag) (push s mc) (push s mv)))
      ((get s 'override-flag)
       (if (get s 'constant-flag) (push s fo) (push s ov)))
      (t (push s us)))

Not as elegant or concise, but does not rely on if and cond as GVs in push.