I've come across this bug whilst using the Dart language server,
which is included in the Dart SDK.
Steps to reproduce bug:
- Create example Dart project using Flutter: `flutter create
hello_world`
- Open `hello_world/lib/main.dart` in Emacs
- Start eglot with `M-x eglot RET`
- Make a rudimentary change in the file; ex. add a line break
- Save with `C-x C-s`
- Following text appears in the minibuffer area: `[eglot] Server
reports (type=1): Unknown method textDocument/didSave`
Related bug reports (on GitHub): https://github.com/dart-lang/sdk/issues/36464 and https://github.com/microsoft/language-server-protocol/issues/288
I am using eglot 1.11 (from ELPA) with Emacs 28.2 on Arch.