added optional method chain indentations for emacs major mode

Author: KOMON

rust-mode.el

@@ -49,6 +49,11 @@
   :type 'integer
   :group 'rust-mode)
 
+(defcustom rust-indent-method-chain nil
+  "Indent Rust method chains, aligned by the '.' operators"
+  :type 'boolean
+  :group 'rust-mode)
+
 (defun rust-paren-level () (nth 0 (syntax-ppss)))
 (defun rust-in-str-or-cmnt () (nth 8 (syntax-ppss)))
 (defun rust-rewind-past-str-cmnt () (goto-char (nth 8 (syntax-ppss))))
@@ -72,6 +77,15 @@
 	(backward-word 1))
       (current-column))))
 
+(defun rust-align-to-method-chain ()
+  (save-excursion
+	(previous-line)
+	(end-of-line)
+	(backward-word 1)
+	(backward-char)
+	(when (looking-at "\\..+\(.*\)\n")
+	  (- (current-column) rust-indent-offset))))
+
 (defun rust-rewind-to-beginning-of-current-level-expr ()
   (let ((current-level (rust-paren-level)))
     (back-to-indentation)
@@ -94,10 +108,13 @@
                    ;; the inside of it correctly relative to the outside.
                    (if (= 0 level)
                        0
+					 (or
+					  (when rust-indent-method-chain
+						(rust-align-to-method-chain))
                      (save-excursion
                        (backward-up-list)
                        (rust-rewind-to-beginning-of-current-level-expr)
-                       (+ (current-column) rust-indent-offset)))))
+                       (+ (current-column) rust-indent-offset))))))
              (cond
               ;; A function return type is indented to the corresponding function arguments
               ((looking-at "->")
@@ -109,6 +126,16 @@
               ;; A closing brace is 1 level unindended
               ((looking-at "}") (- baseline rust-indent-offset))
 
+			  ;;Line up method chains by their .'s
+			  ((when (and rust-indent-method-chain
+						  (looking-at "\..+\(.*\);?\n"))
+				 (or
+				  (let ((method-indent (rust-align-to-method-chain)))
+					(when method-indent
+					  (+ method-indent rust-indent-offset)))
+				  (+ baseline rust-indent-offset))))
+
+			  
               ;; Doc comments in /** style with leading * indent to line up the *s
               ((and (nth 4 (syntax-ppss)) (looking-at "*"))
                (+ 1 baseline))