chore: make suggestion insertion undoable

lsp-inline-completion.el

@@ -33,6 +33,32 @@
 (require 'cl-lib)
 (require 'fringe)
 
+(if (version< emacs-version "29.1")
+    ;; Undo macro probably introduced in 29.1
+    (defmacro lsp-inline-completion--with-undo-amalgamate (&rest body)
+      "Like `progn' but perform BODY with amalgamated undo barriers.
+
+This allows multiple operations to be undone in a single step.
+When undo is disabled this behaves like `progn'."
+      (declare (indent 0) (debug t))
+      (let ((handle (make-symbol "--change-group-handle--")))
+        `(let ((,handle (prepare-change-group))
+               ;; Don't truncate any undo data in the middle of this,
+               ;; otherwise Emacs might truncate part of the resulting
+               ;; undo step: we want to mimic the behavior we'd get if the
+               ;; undo-boundaries were never added in the first place.
+               (undo-outer-limit nil)
+               (undo-limit most-positive-fixnum)
+               (undo-strong-limit most-positive-fixnum))
+           (unwind-protect
+               (progn
+                 (activate-change-group ,handle)
+                 ,@body)
+             (progn
+               (accept-change-group ,handle)
+               (undo-amalgamate-change-group ,handle))))))
+  (defalias 'lsp-inline-completion--with-undo-amalgamate 'with-undo-amalgamate))
+
 (defun lsp-inline-completion--params (implicit &optional identifier position)
   "Returns a InlineCompletionParams instance"
   (lsp-make-inline-completion-params
@@ -281,7 +307,9 @@ text range that was updated by the completion"
       (delete-region start end))
 
     ;; Insert suggestion, keeping the cursor at the start point
-    (insert text)
+    (lsp-inline-completion--with-undo-amalgamate
+      (insert text))
+
     (setq text-insert-end (point))
 
     ;; If a template, format it -- keep track of the end position!