Does imenu sopport sub-indexes?

Question

I'm trying to add support for imenu in a major mode I currently writing.
Reading documentation I've found that its API looks simple and all I want to do is to write a function and bind it to imenu-create-index-function.

Documentation for imenu--index-alist also declares something called nested sub-alist:

A nested sub-alist element looks like (INDEX-NAME . SUB-ALIST). The function ‘imenu--subalist-p’ tests an element and returns t if it is a sub-alist.

Does it mean that one could make imenu have nested structure like?

- index 1
  - sub-index
    - ...
- index 2

I've tried to return following from funciton bound to imenu-create-index-function:

'(("item 1" . '(("sub-item" . 1))) ("item 2" . 1))

And error says that it violates integer-or-marker-p at '(("sub-item" . 1)).

If nested structures are possible, how to form them?

Answer 1

It is possible to represent structured menu with imenu.

A valid alist shape could be:

(list
 (list "Title 1"
       (list "Title 11"
             '("Index Name 1" . 1)
             '("Index Name 2" . 1)))
 (list "Title 2"
       '("Index Name 21" . 1)
       '("Index Name 22" . 1)))

The error was caused by quoting of '(("sub-item" . 1)) form.