bug#64784: 30.0.50; Eglot: Lisp error: (wrong-type-argument number-or-marker-p return) in eglot--post-self-insert-hook

bug#64784: 30.0.50; Eglot: Lisp error: (wrong-type-argument number-or-marker-p return) in eglot--post-self-insert-hook

[Tassilo Horn]

I'm in a rust-ts-mode buffer and ran eglot.  When I hit RET (bound to
newline), I get the following error:

Debugger entered--Lisp error: (wrong-type-argument number-or-marker-p return)
  eglot--post-self-insert-hook()
  self-insert-command(1)
  newline(nil 1)
  funcall-interactively(newline nil 1)
  call-interactively(newline nil nil)
  command-execute(newline)


In GNU Emacs 30.0.50 (build 56, x86_64-pc-linux-gnu, GTK+ Version
 3.24.38, cairo version 1.17.8) of 2023-07-21 built on thinkpad-t440p
Repository revision: c55e67081e9873a32b6e665e44f3e5a9c301255f
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bug#64784: 30.0.50; Eglot: Lisp error: (wrong-type-argument number-or-marker-p return) in eglot--post-self-insert-hook

[Eli Zaretskii]

> From: Tassilo Horn <thorn@fastmail.fm>
> Date: Sat, 22 Jul 2023 07:06:58 +0200
> 
> 
> I'm in a rust-ts-mode buffer and ran eglot.  When I hit RET (bound to
> newline), I get the following error:
> 
> Debugger entered--Lisp error: (wrong-type-argument number-or-marker-p return)
>   eglot--post-self-insert-hook()
>   self-insert-command(1)
>   newline(nil 1)
>   funcall-interactively(newline nil 1)
>   call-interactively(newline nil nil)
>   command-execute(newline)

This is because eglot--post-self-insert-hook assumes last-input-event
is a character:

 (defun eglot--post-self-insert-hook ()
   "Set `eglot--last-inserted-char', maybe call on-type-formatting."
   (setq eglot--last-inserted-char last-input-event)
   (let ((ot-provider (eglot--server-capable :documentOnTypeFormattingProvider))
	 ;; transform carriage return into line-feed
	 (adjusted-ie (if (= last-input-event 13) 10 last-input-event)))
                          ^^^^^^^^^^^^^^^^^^^^^^^

But in this case we get the symbol 'newline' as the value.

The easy way out is to use characterp before comparing with =, but I
actually think there's a deeper problem here, because the code which
uses this post-self-insert-hook _wants_ to process inserted newlines.
So I think a better fix here would be to use last-command-event, not
last-input-event.  All the other post-self-insert-hook implementations
use that, AFAICT.

Stefan, am I right?  Can last-command-event, when accessed from
post-self-insert-hook, ever be something other than a character?

bug#64784: 30.0.50; Eglot: Lisp error: (wrong-type-argument number-or-marker-p return) in eglot--post-self-insert-hook

[João Távora]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Tassilo Horn <thorn@fastmail.fm>
>> Date: Sat, 22 Jul 2023 07:06:58 +0200
>> 
>> 
>> I'm in a rust-ts-mode buffer and ran eglot.  When I hit RET (bound to
>> newline), I get the following error:
>> 
>> Debugger entered--Lisp error: (wrong-type-argument number-or-marker-p return)
>>   eglot--post-self-insert-hook()
>>   self-insert-command(1)
>>   newline(nil 1)
>>   funcall-interactively(newline nil 1)
>>   call-interactively(newline nil nil)
>>   command-execute(newline)
>
> This is because eglot--post-self-insert-hook assumes last-input-event
> is a character:
>
>  (defun eglot--post-self-insert-hook ()
>    "Set `eglot--last-inserted-char', maybe call on-type-formatting."
>    (setq eglot--last-inserted-char last-input-event)
>    (let ((ot-provider (eglot--server-capable :documentOnTypeFormattingProvider))
> 	 ;; transform carriage return into line-feed
> 	 (adjusted-ie (if (= last-input-event 13) 10 last-input-event)))
>                           ^^^^^^^^^^^^^^^^^^^^^^^
>
> But in this case we get the symbol 'newline' as the value.
>
> The easy way out is to use characterp before comparing with =, but I
> actually think there's a deeper problem here, because the code which
> uses this post-self-insert-hook _wants_ to process inserted newlines.
> So I think a better fix here would be to use last-command-event, not
> last-input-event.  All the other post-self-insert-hook implementations
> use that, AFAICT.
>
> Stefan, am I right?  Can last-command-event, when accessed from
> post-self-insert-hook, ever be something other than a character?

Even before Stefan answers, 'last-command-event' sounds right to me.  In
latest master, I've replaced the previous hacky solution with a
simplified one based on this 'last-command-event' and it doesn't need
any translation and works correctly on both TTY and GUI Emacs.

Tassilo, can you test?

João

bug#64784: 30.0.50; Eglot: Lisp error: (wrong-type-argument number-or-marker-p return) in eglot--post-self-insert-hook

[Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors]

>> Stefan, am I right?  Can last-command-event, when accessed from
>> post-self-insert-hook, ever be something other than a character?

In theory it's possible, but in practice, `last-command-event` is what
`self-insert-command` uses as "the char to insert", so it's definitely
more correct than `last-input-event`.


        Stefan

bug#64784: 30.0.50; Eglot: Lisp error: (wrong-type-argument number-or-marker-p return) in eglot--post-self-insert-hook

[Tassilo Horn]

João Távora <joaotavora@gmail.com> writes:

Hi João,

> Even before Stefan answers, 'last-command-event' sounds right to me.
> In latest master, I've replaced the previous hacky solution with a
> simplified one based on this 'last-command-event' and it doesn't need
> any translation and works correctly on both TTY and GUI Emacs.
>
> Tassilo, can you test?

I can say at least that the error is gone.  Thank you!

(The below isn't actually related to the bug but to the feature the code
is providing.)

And now I also looked what that code is actually doing: you do
eglot-format after some trigger characters which seem to be queried from
the LS.  In my case of rust-analyzer, that seems to be

  (:firstTriggerCharacter "=" :moreTriggerCharacter ["." ">" "{"])

eglot-format works good in that buffer and seems to do exactly what
rustfmt also does.  Here I have a problem with rust-ts-mode which seems
to have a sightly different idea about the indentation of some
constructs, e.g., eglot-format and rustfmt say this is "correct"

    fn is_prev_next_window_variant(&self) -> bool {
        matches!(
            self,
            SwayrCommand::NextWindow { .. }
                | SwayrCommand::PrevWindow { .. }
                | SwayrCommand::NextTiledWindow { .. }
                | SwayrCommand::PrevTiledWindow { .. }
                | SwayrCommand::NextTabbedOrStackedWindow { .. }
                | SwayrCommand::PrevTabbedOrStackedWindow { .. }
                | SwayrCommand::NextFloatingWindow { .. }
                | SwayrCommand::PrevFloatingWindow { .. }
                | SwayrCommand::NextWindowOfSameLayout { .. }
                | SwayrCommand::PrevWindowOfSameLayout { .. }
                | SwayrCommand::NextMatchingWindow { .. }
                | SwayrCommand::PrevMatchingWindow { .. }
        )
    }

while rust-ts-mode prefers this:

    fn is_prev_next_window_variant(&self) -> bool {
        matches!(
            self,
            SwayrCommand::NextWindow { .. }
            | SwayrCommand::PrevWindow { .. }
            | SwayrCommand::NextTiledWindow { .. }
            | SwayrCommand::PrevTiledWindow { .. }
            | SwayrCommand::NextTabbedOrStackedWindow { .. }
            | SwayrCommand::PrevTabbedOrStackedWindow { .. }
            | SwayrCommand::NextFloatingWindow { .. }
            | SwayrCommand::PrevFloatingWindow { .. }
            | SwayrCommand::NextWindowOfSameLayout { .. }
            | SwayrCommand::PrevWindowOfSameLayout { .. }
            | SwayrCommand::NextMatchingWindow { .. }
            | SwayrCommand::PrevMatchingWindow { .. }
        )
    }

I actually like the rust-ts-mode variant better but don't find a
(stable) knob in the rustfmt.config to make it agree.  Anyway, I have no
strong preference but frequently produce such needless whitespace
changes during editing (which, of course, cargo fmt will "repair").

So is there a way to stop the indentation wars?  Maybe if I could make
it so that return and tab would also be considered as trigger characters
for eglot-format?

Bye,
Tassilo

bug#64784: LSP vs Emacs indentation [Was: bug#64784: 30.0.50; Eglot: Lisp error: (wrong-type-argument number-or-marker-p return) in eglot--post-self-insert-hook]

[João Távora]

Tassilo Horn <tsdh@gnu.org> writes:

>> Tassilo, can you test?
> I can say at least that the error is gone.  Thank you!

In that case, I'm closing, but we should keep chatting because this
matter interests me as well.  In fact, let's move this to Emacs-devel.

> So is there a way to stop the indentation wars [between LSP and Emacs's]?

There's quite a bit of overlap in indentation functionality, yes.  For
example, in non-ts c++-mode, there are a lot of indentation knobs, and
they can probably do all this.  But configuring them is difficult (for
me), and I'm not sure I haven't seen at a bug or two.  In practice, I've
accepted I'll never get them to match my team's .clang-format
completely.

A way to "stop" the war is to get one of the sides to surrender.  To
make the LSP side lose, just add symbols to
'eglot-ignored-server-capabilities', like
':documentOnTypeFormattingProvider'.

> Maybe if I could make it so that return and tab would also be
> considered as trigger characters for eglot-format?

If your aim is to make the LSP side "win", I don't think you should use
the "trigger character" technique specifically.  But in Emacs you can of
course bind keys to commands that invoke 'eglot-format' synchronously.

Even better, I think the most correct way is to buffer-locally set
'indent-line-function' and 'indent-region-function', so you can keep the
familiar feeling of TAB.

I've tested this:

* Setting 'indent-region-function' simply to 'eglot-format' apparently
  works.  (Not in cc-mode, which has a tendency for wheel-reinvention.
  Or who knows original invention...  but in any case it's probably time
  for me to move on to c++-ts-mode)

* As to 'indent-line-function', there's no Eglot command that's exactly
  compatible with the protocol, but it's pretty easy to make one:

    (defun eglot-indent-line ()
      (eglot-format (line-beginning-position) (line-end-position)))

After setting 'indent-line-function' and 'indent-region-function' like
this, things seem to work well at first.  But simple things like RET
('newline') fail.  I haven't investigated.  Maybe it's becasue of
electric-indent-mode?  Or maybe just because of the fact that
`eglot-format` asks the language server to do more than just indenting,
namely it also inserts newlines.  Or maybe I'm just not passing in the
correct range.

And then there are the annoying messages in the echo area about edits
successfully applied, but that's easily solved.

I hope you (and/or others) can give this approach (or variations
thereof) some testing.  Maybe with other LSP servers and/or style files.

The reason I find this interesting it that it would IMO not only solve
the indentation wars, it solves fundamental problems of limited-context
indenters such as c++-ts-mode.  Consider the C/C++ textual preprocessor
macros: probably no tree-sitter mode can know exactly what they mean and
how to indent the surrounding code, but a sufficiently smart
project-knowing LSP can.

Are there drawbacks to this "LSP-wins" approach to indentation?
Probably.  Chief among them LSP is very slow when compared things in the
same address space, like an Elisp function or a dynamically linked C
library.

My early impression is that this fact almost certainly matters for
LSP-driven fontification, but not for indentation.

In summary, if we can get a successful approach that feels right for
Emacs users (mostly regarding TAB, newline and region-indenting), maybe
we can enshrine LSP-powered indentation in Eglot-managed buffers just
like we do for Xref, Flymake, Imenu, etc...

João