bug#67287: 29.1; hs-set-up-overlay messes up indent-sexp

[João Pedro]

Greetings!

When setting `hs-set-up-overlay' to a custom value, such as the one in
the docstring for the variable, it messes up the behaviour of
`indent-sexp' when it is called "before" the s-expression.

Steps to reproduce:

1. Go to any lisp buffer e.g. *scracth*
2. Paste the following piece of code

    (setq hs-set-up-overlay
          (lambda (ov)
            (when (eq 'code (overlay-get ov 'hs))
              (overlay-put ov 'display
                           (propertize
                            (format " ... <%d>"
                                    (count-lines (overlay-start ov)
                                                 (overlay-end ov)))
                            'face 'font-lock-type-face)))))

3. Evaluate it
4. Enable `hs-minor-mode'
5. Hide the block with `hs-hide-block' (need to be on the beginning line
   of the forms)
6. Move point either to the first opening parenthesis or the the empty
   line before the `setq' form

   (setq
   ^----

7. Call `indent-sexp'
8. Open the block with `hs-show-block'

You should see the following:

    (setq hs-set-up-overlay
          (lambda (ov)
            (when (eq 'code (overlay-get ov 'hs))
              (overlay-put ov 'display
                           (propertize
                            (format " ... <%d>"
                                    (count-lines (overlay-start ov)
                                                 (overlay-end ov)))
                            )

I tried to investigate why it does that, but couldn't really get to the
root cause. It seems that its only affected when we're setting the
`display' prop of the overlay, but I couldn't confirm it either.

Best regards,

-- 
João Pedro de A. Paula
IT bachelors at Universidade Federal do Rio Grande do Norte (UFRN)