bug#64391: buffer narrowing slowdown regression in emacs 29

[Stefan Monnier]

> Whoops, indeed.  (symbolp (eval (cadr rest))) would work,

No, it wouldn't work: we can't (in general) decide at macroexpansion
time whether the expression will return a symbol at runtime.

> but somehow I think it's not TRT and there's a more idiomatic way to
> do that.

Yes: don't do it, or do it via a runtime check rather than
a compile-time check.  But here I don't see any benefit to imposing that
LABEL evaluates to a symbol.


        Stefan