Change Rust language server to rust-analyzer, drop rls

rust-analyzer is the officially blessed Language Server for Rust:
rust-lang/rfcs#2912

Also drop the special support code for RLS.

* eglot.el (eglot-server-programs): Change rust-mode language server
from rls to rust-analyzer.
(eglot-rls, jsonrpc-connection-ready-p)
(eglot-handle-notification): Delete.
* README.md: Update references for RLS to point to rust-analyzer.

Author: skangas

README.md

@@ -67,7 +67,7 @@ find-library` can help you tell if that happened.
 * R's [languageserver][r-languageserver]
 * Racket's [racket-langserver][racket-langserver]
 * Ruby's [solargraph][solargraph]
-* Rust's [rls][rls]
+* Rust's [rust-analyzer][rust-analyzer]
 * Scala's [metals][metals]
 * TeX/LaTeX's [Digestif][digestif]
 * VimScript's [vim-language-server][vim-language-server]
@@ -467,7 +467,7 @@ User-visible differences:
   connection name;
 - Pretty interactive mode-line section for live tracking of server
   communication;
-- Automatically restarts frequently crashing servers (like RLS);
+- Automatically restarts frequently crashing servers;
 - Slow-to-start servers start asynchronously in the background;
 - Server-initiated edits are confirmed with the user;
 - Diagnostics work out-of-the-box (no `flycheck.el` needed);
@@ -517,7 +517,7 @@ Under the hood:
 [r-languageserver]: https://cran.r-project.org/package=languageserver
 [racket-langserver]: https://github.com/jeapostrophe/racket-langserver
 [solargraph]: https://github.com/castwide/solargraph
-[rls]: https://github.com/rust-lang-nursery/rls
+[rust-analyzer]: https://github.com/rust-analyzer/rust-analyzer
 [metals]: https://scalameta.org/metals/
 [digestif]: https://github.com/astoff/digestif
 [vim-language-server]: https://github.com/iamcco/vim-language-server

eglot.el

@@ -142,7 +142,7 @@ chosen (interactively or automatically)."
                       when probe return (cons probe args)
                       finally (funcall err)))))))
 
-(defvar eglot-server-programs `((rust-mode . (eglot-rls "rls"))
+(defvar eglot-server-programs `((rust-mode . ("rust-analyzer"))
                                 (cmake-mode . ("cmake-language-server"))
                                 (vimrc-mode . ("vim-language-server" "--stdio"))
                                 (python-mode
@@ -2983,25 +2983,6 @@ If NOERROR, return predicate, else erroring function."
   (when (eq ?! (aref arg 1)) (aset arg 1 ?^))
   `(,self () (re-search-forward ,(concat "\\=" arg)) (,next)))
 
-
-;;; Rust-specific
-;;;
-(defclass eglot-rls (eglot-lsp-server) () :documentation "Rustlang's RLS.")
-
-(cl-defmethod jsonrpc-connection-ready-p ((server eglot-rls) what)
-  "Except for :completion, RLS isn't ready until Indexing done."
-  (and (cl-call-next-method)
-       (or ;; RLS normally ready for this, even if building.
-        (eq :textDocument/completion what)
-        (pcase-let ((`(,_id ,what ,done ,_detail) (eglot--spinner server)))
-          (and (equal "Indexing" what) done)))))
-
-(cl-defmethod eglot-handle-notification
-  ((server eglot-rls) (_method (eql window/progress))
-   &key id done title message &allow-other-keys)
-  "Handle notification window/progress."
-  (setf (eglot--spinner server) (list id title done message)))
-
 
 ;;; eclipse-jdt-specific
 ;;;