Completing deletes too much text (with snippets or TextEdits)

[mkcms]

Given this file

int foo(int);
int bar(int);
int baz(int);

int main () {
    foo(bar(b));
}

When I set point to 71 and complete to 'baz', I end up with

int foo(int);
int bar(int);
int baz(int);

int main () {
    foo(bar(baz(int));
}

(notice that Emacs deleted one parenthesis at the end of completed line)

This happens if either TextEdits or snippets are present in the completion.
The reason is that the completion provided to :exit-function is not the inserted text, but the whole completed symbol, from car of completion bounds to point.
In this case Emacs deletes one to many character because the completed symbol is b. If the completed symbol is ba, Emacs will delete 2 characters, etc.

Events:

client-request (id:2) Tue Nov 20 13:50:16 2018:
(:jsonrpc "2.0" :id 2 :method "textDocument/completion" :params
	  (:textDocument
	   (:uri "file:///tmp/prog.cpp")
	   :position
	   (:line 5 :character 13)))

server-reply (id:2) Tue Nov 20 13:50:16 2018:
(:id 2 :jsonrpc "2.0" :result
     (:isIncomplete :json-false :items
		    [(:detail "int" :filterText "bar" :insertText "bar(${1:int})" :insertTextFormat 2 :kind 3 :label " bar(int)" :sortText "3f2cccccbar" :textEdit
			      (:newText "bar(${1:int})" :range
					(:end
					 (:character 13 :line 5)
					 :start
					 (:character 12 :line 5))))
		     (:detail "int" :filterText "baz" :insertText "baz(${1:int})" :insertTextFormat 2 :kind 3 :label " baz(int)" :sortText "3f2cccccbaz" :textEdit
			      (:newText "baz(${1:int})" :range
					(:end
					 (:character 13 :line 5)
					 :start
					 (:character 12 :line 5))))
		     (:filterText "bool" :insertText "bool" :insertTextFormat 2 :kind 14 :label " bool" :sortText "3f800000bool" :textEdit
				  (:newText "bool" :range
					    (:end
					     (:character 13 :line 5)
					     :start
					     (:character 12 :line 5))))]))

[joaotavora]

Can we try just undo ing everything? Perhaps that works as is safe for both company and vanilla completion-at-point. Otherwise we have to save some info lexically and recover it when we want the snippet or textEdit approach.

[mkcms]

Can we try just undo ing everything?

Hmm, I tried it a bit and with emacs -Q I get

user-error: No further undo information

in new buffers. When undo-list is not empty, it doesn't appear to work reliably either.

I also tried using change groups which I cancel in :exit-function. This worked pretty well without company. With company-mode it didn't undo the changes at all.
Another option is basically saving the line at point and then in :exit-function deleting the current line and using that. Although that is very ugly...

However I got the best results with just using the bounds which we already calculate from (bounds-of-thing-at-point 'symbol). E.g. just something like this

diff --git a/eglot.el b/eglot.el
index d9c1c3a..fe68f87 100644
--- a/eglot.el
+++ b/eglot.el
@@ -1610,7 +1610,9 @@ is not active."
                             (eglot--snippet-expansion-fn))))
                (when (or fn textEdit)
                  ;; Undo the completion
-                 (delete-region (- (point) (length comp)) (point)))
+                 (delete-region (+ (- (point) (length comp))
+                                   (if bounds (- (cdr bounds) (car bounds)) 0))
+                                (point)))
                (cond (textEdit
                       (cl-destructuring-bind (&key range newText) textEdit
                         (pcase-let ((`(,beg . ,end) (eglot--range-region range)))

[joaotavora]

However I got the best results with just using the bounds which we already calculate from (bounds-of-thing-at-point 'symbol). E.g. just something like this

Good. Let's go with this then. Just add another line of comment or so after "Undo the completion" sumarrily explaining the problem and the strategy.

And if possible add a test for one of these newer servers.

Thanks!

[mkcms]

And if possible add a test for one of these newer servers.

Alright, I will also add a general test for TextEdits in completion. This will require downloading or building a server which supports them on travis though. Although maybe one of the servers we use already supports them, I will check.