emacs-31 83ec0fd8f33: Eglot: prevent showDocument disruption of sync requests (bug#81538)

branch: emacs-31
commit 83ec0fd8f33e36672032201862cbf500e0063733
Author: João Távora <[email protected]>
Commit: João Távora <[email protected]>

    Eglot: prevent showDocument disruption of sync requests (bug#81538)
    
    This couldn't be reproduced here, but seems nevertheless possible.  The
    previous (run-at-time 0...) technique for the window/showDocument
    handling never really avoided the fact that that timer could kick during
    the accept-process-output of jsonrpc-request, thus happening before the
    response to the original request.  Since the handling evolves a lot of
    output to send to the process, it could be interrupted by the 'throw'
    that's meant to exit abort 'accept-process-output' (and only that).
    
    This commit should ensure the sequence is always this one.
    
    a1. -> adals/ff-thingy sync client request
    b1.   <- window/showDocument server request
    b2.   -> window/showDocument client response (after scheduling 'c')
    a2. <- ada/ff-thingy server response
    c.  -> f-f-no-select, Eglot sends the large didOpen notification
    
    * lisp/progmodes/eglot.el (eglot-handle-request): Maybe use
    "post command" once trick.
---
 lisp/progmodes/eglot.el | 29 ++++++++++++++++-------------
 1 file changed, 16 insertions(+), 13 deletions(-)

diff --git a/lisp/progmodes/eglot.el b/lisp/progmodes/eglot.el
index 1f4f6abbd91..e53d2a08159 100644
--- a/lisp/progmodes/eglot.el
+++ b/lisp/progmodes/eglot.el
@@ -2962,19 +2962,22 @@ THINGS are either registrations or unregisterations (sic)."
     (cond
      ((eq external t) (browse-url uri))
      ((file-readable-p (setq filename (eglot-uri-to-path uri)))
-      ;; Use run-with-timer to avoid nested client requests like the
-      ;; "synchronous imenu" floated in bug#62116 presumably caused by
-      ;; which-func-mode.
-      (run-with-timer
-       0 nil
-       (lambda ()
-         (with-current-buffer (find-file-noselect filename)
-           (cond (takeFocus
-                  (pop-to-buffer (current-buffer))
-                  (select-frame-set-input-focus (selected-frame)))
-                 ((display-buffer (current-buffer))))
-           (when selection
-             (eglot--goto selection))))))
+      ;; Really ensure this runs when it is safe to run it.
+      ;; run-with-timer avoid nested client requests like the
+      ;; "synchronous imenu" floated in bug#62116, while the
+      ;; "post-command once" trick is for bug#81538.
+      (cl-labels ((findit ()
+                  (remove-hook 'post-command-hook #'findit)
+                  (with-current-buffer (find-file-noselect filename)
+                    (cond (takeFocus
+                           (pop-to-buffer (current-buffer))
+                           (select-frame-set-input-focus (selected-frame)))
+                          ((display-buffer (current-buffer))))
+                    (when selection
+                      (eglot--goto selection)))))
+                (if this-command
+                    (add-hook 'post-command-hook #'findit)
+                  (run-at-time 0 nil #'findit))))
      (t (setq success :json-false)))
     `(:success ,success)))