bug#56185: 29.0.50; imenu with imenu-use-popup-menu fails for *Rescan* item

[Lars Ingebrigtsen <larsi@gnus.org>]

Visuwesh <visuweshm@gmail.com> writes:

> When imenu-use-popup-menu is non-nil and one selects the *Rescan* item,
> imenu fails with the following backtrace,
>
>     Debugger entered--Lisp error: (error "Invalid `key-parse' syntax: %S" ["*Rescan*"])
>       lookup-key((keymap "sh" ("*Rescan*" "*Rescan*" . #f(compiled-function () (interactive nil) #<bytecode -0x1823bf90e9c446ac>)) ("x" "x" . #f(compiled-function () (interactive nil) #<bytecode -0x19fbbb6b7dca5348>)) ("y" "y" . #f(compiled-function () (interactive nil) #<bytecode -0x19fbbb6b7da17348>))) ["*Rescan*"])
>       popup-menu((keymap "sh" ("*Rescan*" "*Rescan*" . #f(compiled-function () (interactive nil) #<bytecode -0x1823bf90e9c446ac>)) ("x" "x" . #f(compiled-function () (interactive nil) #<bytecode -0x19fbbb6b7dca5348>)) ("y" "y" . #f(compiled-function () (interactive nil) #<bytecode -0x19fbbb6b7da17348>))) 105)
>       imenu--mouse-menu((("*Rescan*" . -99) ("x" . #<marker at 1 in sh>) ("y" . #<marker at 7 in sh>)) 105)

I think something has gone missing here over the years?  Or I'm
misreading the commits; that's also possible.

We basically end up with this:

(lookup-key
 '(keymap "sh"
	  ("*Rescan*" "*Rescan*" . ignore))
 ["*Rescan*"])

Which now signals an error; in Emacs 28 it just silently returned nil.
But the problem here is that that's not a valid menu syntax -- the first
element should be a symbol, not a string.  So I've now fixed that in
Emacs 29, which makes this work.  But I'm wondering whether there's
something more er fundamentally wrong somewhere...

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no