Error if window with link is deleted while following a link

[dsedivec]

Steps to reproduce:

1. Start with a fresh Emacs.
2. Configure MELPA.
3. Install link-hint and window-purpose from MELPA.
4. Eval (progn (purpose-mode 1) (purpose-x-popwin-setup)) to turn on window-purpose and install its popwin-like emulation. popwin will make "popup windows", such as windows containing help buffers, automatically go away.
5. Bring up any help that contains a link, such as C-h f auto-fill-mode RET.
6. Select the "*Help*" buffer/window, e.g. C-x o.
7. M-x link-hint-open-link RET

link-hint does successfully follow the link, but you get an error such as internal--before-with-selected-window: Wrong type argument: window-valid-p, #<window 18>. Here's the backtrace:

Debugger entered--Lisp error: (wrong-type-argument window-valid-p #<window 24>)
  window-frame(#<window 24>)
  internal--before-with-selected-window(#<window 24>)
  link-hint--action(:open (:pos 61 :win #<window 24> :args "(auto-fill-mode /Users/dale/Applications/Emacs.app..." :type link-hint-help-link))
  link-hint--one(:open)
  link-hint-open-link()
  funcall-interactively(link-hint-open-link)
  call-interactively(link-hint-open-link record nil)
  command-execute(link-hint-open-link record)
  execute-extended-command(nil "link-hint-open-link" "link-hint-open-link")
  funcall-interactively(execute-extended-command nil "link-hint-open-link" "link-hint-open-link")
  call-interactively(execute-extended-command nil nil)
  command-execute(execute-extended-command)

I believe this happens because window-purpose's popwin emulation deletes the window containing "*Help*" in the middle of link-hint following the link.

Specifically, I am guessing that link-hint follows the link around line 993 in link-hint--action, which involves changing the window configuration, which in turn triggers window-purpose to close the popup "*Help*" window. But then link-hint tries to use the now-invalid link-win window at line 1006 in with-selected-window. (internal--before-with-selected-window is part of with-selected-window.)

I'm not sure what the appropriate fix is here. Change line 1006 to (with-selected-window (if (window-valid-p link-win) (current-window)) ...)? Or avoid this branch of the cond entirely if the link-win is no longer valid? There's also the comment right around here about using a "temporary window" that I don't fully understand.

Which is to say, I can't open a PR because I don't know how you would like to fix this! But please let me know if you have any problems understanding or reproducing the above.

I am using Emacs 27.0.50 (rebuilt from master earlier today) on macOS with the latest link-hint and window-purpose from MELPA.

[noctuid]

Thanks for the detailed report. I've updated it to handle this situation. It should work with the last commit; let me know if you have any issues.

[dsedivec]

FYI this seems fixed to me, thank you very much!