Allow non-binding VARLIST entries in let*

[wtianyi]

When VARLIST in let* is purely used for its side-effect and have no variable, do nothing.

For example, https://github.com/emacs-mirror/emacs/blob/73d2b829f06124fec8b65eebc68e87da48808086/lisp/comint.el#L3554

[Fuco1]

The let and let* forms don't support such syntax. The code you linked is a when-let* macro which probably allows it to chain conditions, but in the expansion it's no longer without a variable binding.

Which means we can no longer alias when-let* to let*, because that would allow invalid let* forms to pass. Since the form is available, we could add a check on the let-flavour though, but it's a bit more work.

[wtianyi]

Ah thanks for the information! I should have looked at the syntax more closely. Not sure if I'll be able to, but if I have a more proper fix I'd push it here.

[wtianyi]

Actually I have some more questions: Currently elsa--analyse:let* breaks with an Invalid read syntax: "Expected form" error encountering a (VALUEFORM) entry (not binding anything) in the VARLIST. Do we want to give more informative lint in such case? How can that be done?