master a6ef458e383: Eglot: partial fix for middle-of-symbol completions

[João Távora]

branch: master
commit a6ef458e3831001b0acad57cf8fa75b77a4aff3f
Author: João Távora <joaotavora@gmail.com>
Commit: João Távora <joaotavora@gmail.com>

    Eglot: partial fix for middle-of-symbol completions
    
    * lisp/progmodes/eglot.el (eglot-completion-at-point): Fix
    completion reversion in :exit-function.
    
    In a rust-ts-mode buffer such as this main.rs file
    
      fn main() {
        let v: usize = 1;
        v.c<cursor-here>1234.1234567890
      }
    
    the server wants to edit the line to read, after C-M-i and selecting
    "count_ones"
    
        v.count_ones<cursor-here>.1234567890
    
    But it couldn't apply the edit to the correct initial state because
    that state wasn't correctly restored.  This commit fixes that.
    
    However, if the initial state is
    
        v.count_on1234.1234567890
    
    then completion still fails, because the 'try-completion' call in
    eglot-completion-at-point will just return complete to "count_ones"
    and Emacs doesn't consider this a completion "exit", so it'll
    completely ignore the exit function.
    
    I think 'try-completion' (and 'test-completion') simply can't be used
    here (for one, they obey styles, and styles are off-limits in LSP),
    but I'll leave that for another commit.
    
    Github-reference: https://github.com/joaotavora/eglot/issues/1339
---
 lisp/progmodes/eglot.el | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/lisp/progmodes/eglot.el b/lisp/progmodes/eglot.el
index 8235bbe1751..d777e488c43 100644
--- a/lisp/progmodes/eglot.el
+++ b/lisp/progmodes/eglot.el
@@ -3031,6 +3031,7 @@ for which LSP on-type-formatting should be requested."
     (let* ((server (eglot--current-server-or-lose))
            (bounds (or (bounds-of-thing-at-point 'symbol)
                        (cons (point) (point))))
+           (bounds-string (buffer-substring (car bounds) (cdr bounds)))
            (sort-completions
             (lambda (completions)
               (cl-sort completions
@@ -3213,9 +3214,10 @@ for which LSP on-type-formatting should be requested."
                         ;; Revert buffer back to state when the edit
                         ;; was obtained from server. If a `proxy'
                         ;; "bar" was obtained from a buffer with
-                        ;; "foo.b", the LSP edit applies to that'
+                        ;; "foo.b", the LSP edit applies to that
                         ;; state, _not_ the current "foo.bar".
                         (delete-region orig-pos (point))
+                        (insert (substring bounds-string (- orig-pos (car 
bounds))))
                         (eglot--dbind ((TextEdit) range newText) textEdit
                           (pcase-let ((`(,beg . ,end)
                                        (eglot-range-region range)))