bug#69809: 30.0.50; flymake: error in process sentinel

[Eshel Yaron]

Eshel Yaron <me@eshelyaron.com> writes:

[...]

> This issue bothered me as well.  Here's a recipe for reproducing on
> master, with emacs -Q:
>
> 1. (add-hook 'c-mode-hook 'flymake-mode)
> 2. (add-hook 'c-mode-hook 'eglot-ensure)
> 3. Find some C file
>
> This happens because Eglot _restarts_ flymake-mode while flymake-cc's
> process is already running.  Here's a simple fix:
>
> diff --git a/lisp/progmodes/eglot.el b/lisp/progmodes/eglot.el
> index a893a8d749a..c9e1bb7b52d 100644
> --- a/lisp/progmodes/eglot.el
> +++ b/lisp/progmodes/eglot.el
> @@ -2040,7 +2040,7 @@ eglot--managed-mode
>      (unless (eglot--stay-out-of-p 'imenu)
>        (add-function :before-until (local 'imenu-create-index-function)
>                      #'eglot-imenu))
> -    (unless (eglot--stay-out-of-p 'flymake) (flymake-mode 1))
> +    (unless (or (eglot--stay-out-of-p 'flymake) flymake-mode) (flymake-mode 
> 1))
>      (unless (eglot--stay-out-of-p 'eldoc)
>        (add-hook 'eldoc-documentation-functions #'eglot-hover-eldoc-function
>                  nil t)

I realized that the change above has the downside of no longer
immediately initiating a Flymake analysis with Eglot in place.  To
preserve that behavior, maybe something like the following is better:

diff --git a/lisp/progmodes/eglot.el b/lisp/progmodes/eglot.el
index a893a8d749a..6cd48917d47 100644
--- a/lisp/progmodes/eglot.el
+++ b/lisp/progmodes/eglot.el
@@ -2040,7 +2040,8 @@ eglot--managed-mode
     (unless (eglot--stay-out-of-p 'imenu)
       (add-function :before-until (local 'imenu-create-index-function)
                     #'eglot-imenu))
-    (unless (eglot--stay-out-of-p 'flymake) (flymake-mode 1))
+    (unless (eglot--stay-out-of-p 'flymake)
+      (if flymake-mode (flymake-start) (flymake-mode 1)))
     (unless (eglot--stay-out-of-p 'eldoc)
       (add-hook 'eldoc-documentation-functions #'eglot-hover-eldoc-function
                 nil t)