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+;;; ra.el --- Rust analyzer emacs bindings -*- lexical-binding: t; -*-
+;;; Commentary:
+;;; Small utilities for interacting with Rust analyzer.
+;;; Run
+;;;   cargo install --git https://github.com/matklad/rust-analyzer/ ra_cli
+;;; to install the analyzer binary. Then copy-paste the bellow code to
+;;; your `.init.el` and use `ra-extend-selection` and
+;;; `ra-shrink-selection` functions.
+;;; Code:
+
+
+(defvar ra--selections-cache '(0 0 ()))
+(defun ra--cache-tick ()
+  "Get buffer modification count for cache."
+  (nth 0 ra--selections-cache))
+(defun ra--cache-sel ()
+  "Get current selection for cache."
+  (nth 1 ra--selections-cache))
+(defun ra--cache-nth-sel (n)
+  "Get Nth selection."
+  (nth n (nth 2 ra--selections-cache)))
+(defun ra--cache-set-nth-sel (n)
+  "Get Nth selection."
+  (setf (nth 1 ra--selections-cache) n)
+  (nth n (nth 2 ra--selections-cache)))
+
+
+(defun ra-extend-selection ()
+  "Extend START END region to contain the encompassing syntactic construct."
+  (interactive)
+  (let* ((p (point))
+         (m (or (and mark-active (mark)) p))
+         (start (min p m))
+         (end (max p m)))
+    (ra--extend-selection start end)))
+
+
+(defun ra-shrink-selection (start end)
+  "Shrink START END region to contain previous selection."
+  (interactive "r")
+  (ra--freshen-cache start end)
+  (let ((sel-id (ra--cache-sel)))
+    (if (not (= 0 sel-id))
+        (let* ((r (ra--cache-set-nth-sel (- sel-id 1))))
+          (push-mark (nth 0 r) t t)
+          (goto-char (nth 1 r))
+          (setq deactivate-mark nil)))))
+
+; Add this to setup keybinding
+; (require 'rust-mode)
+; (define-key rust-mode-map (kbd "C-w") 'ra-extend-selection)
+; (define-key rust-mode-map (kbd "C-S-w") 'ra-shrink-selection)
+
+
+
+(defun ra--extend-selection (start end)
+  "Extend START END region to contain the encompassing syntactic construct."
+  (ra--freshen-cache start end)
+  (let* ((next-sel-idx (+ 1 (ra--cache-sel)))
+         (r (ra--cache-set-nth-sel next-sel-idx)))
+    (push-mark (nth 0 r) t t)
+    (goto-char (nth 1 r))
+    (setq deactivate-mark nil)))
+
+(defun ra--selections (start end)
+  "Get list of selections for START END from Rust analyzer."
+  (read (with-output-to-string
+          (call-process-region
+           (point-min) (point-max)
+           "ra_cli" nil standard-output nil
+           "extend-selection"
+           (number-to-string start)
+           (number-to-string end)))))
+
+(defun ra--freshen-cache (start end)
+  "Make selection cache up-to-date for current buffer state and START END."
+  (if (not (and
+            (= (buffer-modified-tick) (ra--cache-tick))
+            (equal `(,start ,end) (ra--cache-nth-sel (ra--cache-sel)))))
+      (ra--set-cache start end)))
+
+(defun ra--set-cache (start end)
+  "Set selections cache for current buffer state and START END."
+  (setq ra--selections-cache `(,(buffer-modified-tick) 0 ,(ra--selections start end))))
+
+(provide 'ra)
+;;; ra.el ends here