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+;;; ra-emacs-lsp.el --- Rust analyzer emacs bindings for emacs-lsp -*- lexical-binding: t; -*-
+;;; Code:
+
+(require 'lsp)
+(require 'dash)
+(require 'ht)
+
+;; This currently
+;;  - sets up rust-analyzer with emacs-lsp, giving
+;;    - code actions
+;;    - completion (use company-lsp for proper snippet support)
+;;    - imenu support
+;;    - on-type formatting
+;;    - 'hover' type information & documentation (with lsp-ui)
+;;  - implements source changes (for code actions etc.), except for file system changes
+;;  - implements joinLines (you need to bind rust-analyzer-join-lines to a key)
+;;  - implements extendSelection (either bind rust-analyzer-extend-selection to a key, or use expand-region)
+
+;; What's missing:
+;;  - file system changes in apply-source-change
+;;  - semantic highlighting
+;;  - onEnter, parentModule, findMatchingBrace
+;;  - runnables
+;;  - the debugging commands (syntaxTree and analyzerStatus)
+;;  - lsp-ui doesn't interpret the markdown we return currently and instead displays it raw (https://github.com/emacs-lsp/lsp-ui/issues/220 )
+;;  - more
+
+;; Also, there's a problem with company-lsp's caching being too eager, sometimes
+;; resulting in outdated completions.
+
+(defcustom rust-analyzer-command '("ra_lsp_server")
+  ""
+  :type '(repeat (string)))
+
+(defconst rust-analyzer--notification-handlers
+  '(("rust-analyzer/publishDecorations" . (lambda (_w _p)))))
+
+(defconst rust-analyzer--action-handlers
+  '(("rust-analyzer.applySourceChange" .
+     (lambda (p) (rust-analyzer--apply-source-change-command p)))))
+
+(defun rust-analyzer--uri-filename (text-document)
+  (lsp--uri-to-path (gethash "uri" text-document)))
+
+(defun rust-analyzer--goto-lsp-loc (loc)
+  (-let (((&hash "line" "character") loc))
+    (goto-line (1+ line))
+    (move-to-column character)))
+
+(defun rust-analyzer--apply-text-document-edit (edit)
+  "Like lsp--apply-text-document-edit, but it allows nil version."
+  (let* ((ident (gethash "textDocument" edit))
+         (filename (rust-analyzer--uri-filename ident))
+         (version (gethash "version" ident)))
+    (with-current-buffer (find-file-noselect filename)
+      (when (or (not version) (= version (lsp--cur-file-version)))
+        (lsp--apply-text-edits (gethash "edits" edit))))))
+
+(defun rust-analyzer--apply-source-change (data)
+  ;; TODO fileSystemEdits
+  (--each (-> data (ht-get "workspaceEdit") (ht-get "documentChanges"))
+    (rust-analyzer--apply-text-document-edit it))
+  (-when-let (cursor-position (ht-get data "cursorPosition"))
+    (let ((filename (rust-analyzer--uri-filename (ht-get cursor-position "textDocument")))
+          (position (ht-get cursor-position "position")))
+      (find-file filename)
+      (rust-analyzer--goto-lsp-loc position)
+      )))
+
+(defun rust-analyzer--apply-source-change-command (p)
+  (let ((data (-> p (ht-get "arguments") (car))))
+    (rust-analyzer--apply-source-change data)))
+
+(lsp-register-client
+ (make-lsp-client
+  :new-connection (lsp-stdio-connection (lambda () rust-analyzer-command))
+  :notification-handlers (ht<-alist rust-analyzer--notification-handlers)
+  :action-handlers (ht<-alist rust-analyzer--action-handlers)
+  :major-modes '(rust-mode)
+  :ignore-messages nil
+  :server-id 'rust-analyzer))
+
+(defun rust-analyzer--join-lines-params ()
+  "Join lines params."
+  (list :textDocument (lsp--text-document-identifier)
+        :range (if (use-region-p)
+                   (lsp--region-to-range (region-beginning) (region-end))
+                 (lsp--region-to-range (point) (point)))))
+
+(defun rust-analyzer-join-lines ()
+  (interactive)
+  (->
+   (lsp-send-request (lsp-make-request "rust-analyzer/joinLines"
+                                       (rust-analyzer--join-lines-params)))
+   (rust-analyzer--apply-source-change)))
+
+(with-eval-after-load 'company-lsp
+  ;; company-lsp provides a snippet handler for rust by default that adds () after function calls, which RA does better
+  (setq company-lsp--snippet-functions (assq-delete-all "rust" company-lsp--snippet-functions)))
+
+;; extend selection
+
+(defun rust-analyzer-extend-selection ()
+  (interactive)
+  (-let (((&hash "start" "end") (rust-analyzer--extend-selection)))
+    (rust-analyzer--goto-lsp-loc start)
+    (set-mark (point))
+    (rust-analyzer--goto-lsp-loc end)
+    (exchange-point-and-mark)))
+
+(defun rust-analyzer--extend-selection-params ()
+  "Extend selection params."
+  (list :textDocument (lsp--text-document-identifier)
+        :selections
+        (vector
+         (if (use-region-p)
+             (lsp--region-to-range (region-beginning) (region-end))
+           (lsp--region-to-range (point) (point))))))
+
+(defun rust-analyzer--extend-selection ()
+  (->
+   (lsp-send-request
+    (lsp-make-request
+     "rust-analyzer/extendSelection"
+     (rust-analyzer--extend-selection-params)))
+   (ht-get "selections")
+   (car)))
+
+(defun rust-analyzer--add-er-expansion ()
+  (make-variable-buffer-local 'er/try-expand-list)
+  (setq er/try-expand-list (append
+                            er/try-expand-list
+                            '(rust-analyzer-extend-selection))))
+
+(with-eval-after-load 'expand-region
+  (add-hook 'rust-mode-hook 'rust-analyzer--add-er-expansion))
+
+(provide 'ra-emacs-lsp)
+;;; ra-emacs-lsp.el ends here