gopls reporting is delayed when flymake-no-changes-timeout is set to nil

[ipvych]

Steps to reproduce

• Install gopls language server using go install golang.org/x/tools/gopls@latest
• Make language server available in PATH by running export PATH="${GOPATH:-$HOME/go}/bin:$PATH"
• Save this code in ~/mre.el

(cd "~")

;; download dependencies to file-system
(shell-command "git clone --depth=1 https://github.com/joaotavora/eglot")
(shell-command "git clone --depth=1 https://github.com/dominikh/go-mode.el go-mode")

;; add packages to load-path
(add-to-list 'load-path "~/eglot")
(add-to-list 'load-path "~/go-mode")

(require 'go-mode)
(require 'eglot)
(add-hook 'go-mode-hook #'eglot-ensure)
(setq flymake-no-changes-timeout nil)

(make-directory "~/repr" t)
(find-file "~/repr/test.go")
(insert "
package main
import \"fmt\"
func main() {
	fmt.Println(\"test\")
}")
(save-buffer)

• Run emacs -Q -l ~/mre.el
• Add or remove comment from fmt.Println statement and save buffer - flymake diagnostic will be outdated and contain diagnostic from previous save.

Contents of M-x eglot-events-buffer: https://gist.github.com/ipvych/391ac3103e168b9d0ae75f8322191fa9

System information

• (emacs-build-description):

In GNU Emacs 29.1 (build 1, x86_64-pc-linux-gnu, X toolkit, cairo version
1.16.0, Xaw3d scroll bars)
Windowing system distributor 'The X.Org Foundation', version 11.0.12101008
System Description: NixOS 23.11 (Tapir)

Configured using:
 'configure --prefix=/nix/store/956mdihpqbh2x1bm75xw80zjksgsbpgn-emacs-29.1
 --disable-build-details --with-modules --with-x-toolkit=lucid --with-xft
 --with-cairo --with-native-compilation --with-tree-sitter --with-xinput2'

• gopls version:

golang.org/x/tools/gopls v0.13.2
    golang.org/x/tools/gopls@v0.13.2 h1:Pyvx6MKvatbX3zzZmdGiFRfQZl0ohPlt2sFxO/5j6Ro=

[joaotavora]

ACK. There's not much to do here, except recommending you don't do this customization for Eglot.

When the buffer is saved, Flymake asks for diagnostics, and at that time, the server hasn't yet published the notification that says there are no diagnostics at all. According to the LSP spec, it can take all the time in the world for that.

There is now a "pull diagnostics" specification in LSP that would presumably fix this, but Eglot does not yet support this feature.

Maybe this 100% untested hack will work for you:

(cl-defmethod eglot-handle-notification :after
  (_server (_method (eql textDocument/publishDiagnostics)) &key uri
           &allow-other-keys)
  (when-let ((buffer (find-buffer-visiting (eglot-uri-to-path uri))))
    (with-current-buffer buffer
      (if (and (eq nil flymake-no-changes-timeout)
               (not (buffer-modified-p)))
          (flymake-start t)))))