bug#66759: 30.0.50; Flymake (with Eglot) error cleaning up old overlay

["João Távora" <joaotavora@gmail.com>]

Richard Copley <rcopley@gmail.com> writes:

> On Thu, 26 Oct 2023 at 14:24, João Távora <joaotavora@gmail.com> wrote:
>> Please keep an eye out of this bug.
>
> Thanks, will do.

I've now reproduced the bug consistently.  It happens exactly as you
conjectured.  To test, I temporarily hacked Eglot to take 2 seconds
longer to process each request/notification with this patch:

diff --git a/lisp/progmodes/eglot.el b/lisp/progmodes/eglot.el
index eba66503bf7..48845a889a8 100644
--- a/lisp/progmodes/eglot.el
+++ b/lisp/progmodes/eglot.el
@@ -1488,7 +1488,7 @@ eglot--connect
                      ,@more-initargs)))))
          (spread (lambda (fn) (lambda (server method params)
                                 (let ((eglot--cached-server server))
-                                  (apply fn server method (append params nil))))))
+                                  (run-at-time 2 nil #'apply fn server method (append params nil))))))
          (server
           (apply
            #'make-instance class

And then made sure there was a diagnostic at the end of the file,
changed the file and quickly enough (but only after the changes were
sent to server), deleted the region with the diagnostic at the end of
the file.

Without my fix, I get exactly the (overlayp nil) error you reported.
With the fix, everything works correctly.

So I think with the fix I pushed earlier this bug can be closed, which
I'm doing now.

>> What language server are you using with Eglot btw?

> [1] https://leanprover-community.github.io/learn.html
> [2] https://github.com/leanprover/lean4-mode
> [3] https://github.com/bustercopley/lean4-mode
> [4] https://github.com/joaotavora/eglot/issues/615
> [5] https://github.com/joaotavora/eglot/pull/839

Yeah I know about these PRs.  If you want can start a new report in the
Emacs bug tracker proper (i.e. here) )and direct people to it.  Write a
summary of the situation if you can, and present this Lean4 use case as
a argument.

This gives visibility to more Emacs maintainers, and allows me to ping
specialists like Eli more easily on the matter.

João