path: root/rust-mode.el

;;; rust-mode.el --- A major emacs mode for editing Rust source code

;; Version: 0.2.0
;; Author: Mozilla
;; Url: https://github.com/rust-lang/rust
;; Keywords: languages

;;; Commentary:
;;

;;; Code:

(eval-when-compile (require 'misc))

;; for GNU Emacs < 24.3
(eval-when-compile
  (unless (fboundp 'setq-local)
    (defmacro setq-local (var val)
      "Set variable VAR to value VAL in current buffer."
      (list 'set (list 'make-local-variable (list 'quote var)) val))))

;; Syntax definitions and helpers
(defvar rust-mode-syntax-table
  (let ((table (make-syntax-table)))

    ;; Operators
    (dolist (i '(?+ ?- ?* ?/ ?& ?| ?^ ?! ?< ?> ?~ ?@))
      (modify-syntax-entry i "." table))

    ;; Strings
    (modify-syntax-entry ?\" "\"" table)
    (modify-syntax-entry ?\\ "\\" table)

    ;; _ is a word-char
    (modify-syntax-entry ?_ "w" table)

    ;; Comments
    (modify-syntax-entry ?/  ". 124b" table)
    (modify-syntax-entry ?*  ". 23"   table)
    (modify-syntax-entry ?\n "> b"    table)
    (modify-syntax-entry ?\^m "> b"   table)

    table))

(defgroup rust-mode nil
  "Support for Rust code."
  :link '(url-link "http://www.rust-lang.org/")
  :group 'languages)

(defcustom rust-indent-offset 4
  "Indent Rust code by this number of spaces."
  :type 'integer
  :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))))
(defun rust-rewind-irrelevant ()
  (let ((starting (point)))
    (skip-chars-backward "[:space:]\n")
    (if (looking-back "\\*/") (backward-char))
    (if (rust-in-str-or-cmnt)
        (rust-rewind-past-str-cmnt))
    (if (/= starting (point))
        (rust-rewind-irrelevant))))

(defun rust-align-to-expr-after-brace ()
  (save-excursion
    (forward-char)
    ;; We don't want to indent out to the open bracket if the
    ;; open bracket ends the line
    (when (not (looking-at "[[:blank:]]*\\(?://.*\\)?$"))
      (when (looking-at "[[:space:]]")
	(forward-word 1)
	(backward-word 1))
      (current-column))))

(defun rust-rewind-to-beginning-of-current-level-expr ()
  (let ((current-level (rust-paren-level)))
    (back-to-indentation)
    (while (> (rust-paren-level) current-level)
      (backward-up-list)
      (back-to-indentation))))

(defun rust-mode-indent-line ()
  (interactive)
  (let ((indent
         (save-excursion
           (back-to-indentation)
           ;; Point is now at beginning of current line
           (let* ((level (rust-paren-level))
                  (baseline
                   ;; Our "baseline" is one level out from the indentation of the expression
                   ;; containing the innermost enclosing opening bracket.  That
                   ;; way if we are within a block that has a different
                   ;; indentation than this mode would give it, we still indent
                   ;; the inside of it correctly relative to the outside.
                   (if (= 0 level)
                       0
                     (save-excursion
                       (backward-up-list)
                       (rust-rewind-to-beginning-of-current-level-expr)
                       (+ (current-column) rust-indent-offset)))))
             (cond
              ;; A function return type is indented to the corresponding function arguments
              ((looking-at "->")
               (save-excursion
                 (backward-list)
                 (or (rust-align-to-expr-after-brace)
                     (+ baseline rust-indent-offset))))

              ;; A closing brace is 1 level unindended
              ((looking-at "}") (- 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))

              ;; If we're in any other token-tree / sexp, then:
              (t
               (or
                ;; If we are inside a pair of braces, with something after the
                ;; open brace on the same line and ending with a comma, treat
                ;; it as fields and align them.
                (when (> level 0)
                  (save-excursion
                    (rust-rewind-irrelevant)
                    (backward-up-list)
                    ;; Point is now at the beginning of the containing set of braces
                    (rust-align-to-expr-after-brace)))

                (progn
                  (back-to-indentation)
                  ;; Point is now at the beginning of the current line
                  (if (or
                       ;; If this line begins with "else" or "{", stay on the
                       ;; baseline as well (we are continuing an expression,
                       ;; but the "else" or "{" should align with the beginning
                       ;; of the expression it's in.)
                       (looking-at "\\<else\\>\\|{")

                       (save-excursion
                         (rust-rewind-irrelevant)
                         ;; Point is now at the end of the previous ine
                         (or
                          ;; If we are at the first line, no indentation is needed, so stay at baseline...
                          (= 1 (line-number-at-pos (point)))
                          ;; ..or if the previous line ends with any of these:
                          ;;     { ? : ( , ; [ }
                          ;; then we are at the beginning of an expression, so stay on the baseline...
                          (looking-back "[(,:;?[{}]\\|[^|]|")
                          ;; or if the previous line is the end of an attribute, stay at the baseline...
                          (progn (rust-rewind-to-beginning-of-current-level-expr) (looking-at "#")))))
                      baseline

                    ;; Otherwise, we are continuing the same expression from the previous line,
                    ;; so add one additional indent level
                    (+ baseline rust-indent-offset))))))))))

    ;; If we're at the beginning of the line (before or at the current
    ;; indentation), jump with the indentation change.  Otherwise, save the
    ;; excursion so that adding the indentations will leave us at the
    ;; equivalent position within the line to where we were before.
    (if (<= (current-column) (current-indentation))
        (indent-line-to indent)
      (save-excursion (indent-line-to indent)))))


;; Font-locking definitions and helpers
(defconst rust-mode-keywords
  '("as"
    "box" "break"
    "continue" "crate"
    "do"
    "else" "enum" "extern"
    "false" "fn" "for"
    "if" "impl" "in"
    "let" "loop"
    "match" "mod" "mut"
    "priv" "proc" "pub"
    "ref" "return"
    "self" "static" "struct" "super"
    "true" "trait" "type"
    "unsafe" "use"
    "while"))

(defconst rust-special-types
  '("u8" "i8"
    "u16" "i16"
    "u32" "i32"
    "u64" "i64"

    "f32" "f64"
    "float" "int" "uint"
    "bool"
    "str" "char"))

(defconst rust-re-ident "[[:word:][:multibyte:]_][[:word:][:multibyte:]_[:digit:]]*")
(defconst rust-re-CamelCase "[[:upper:]][[:word:][:multibyte:]_[:digit:]]*")
(defun rust-re-word (inner) (concat "\\<" inner "\\>"))
(defun rust-re-grab (inner) (concat "\\(" inner "\\)"))
(defun rust-re-grabword (inner) (rust-re-grab (rust-re-word inner)))
(defun rust-re-item-def (itype)
  (concat (rust-re-word itype) "[[:space:]]+" (rust-re-grab rust-re-ident)))

(defvar rust-mode-font-lock-keywords
  (append
   `(
     ;; Keywords proper
     (,(regexp-opt rust-mode-keywords 'words) . font-lock-keyword-face)

     ;; Special types
     (,(regexp-opt rust-special-types 'words) . font-lock-type-face)

     ;; Attributes like `#[bar(baz)]` or `#![bar(baz)]` or `#[bar = "baz"]`
     (,(rust-re-grab (concat "#\\!?\\[" rust-re-ident "[^]]*\\]"))
      1 font-lock-preprocessor-face t)

     ;; Syntax extension invocations like `foo!`, highlight including the !
     (,(concat (rust-re-grab (concat rust-re-ident "!")) "[({[:space:][]")
      1 font-lock-preprocessor-face)

     ;; Field names like `foo:`, highlight excluding the :
     (,(concat (rust-re-grab rust-re-ident) ":[^:]") 1 font-lock-variable-name-face)

     ;; Module names like `foo::`, highlight including the ::
     (,(rust-re-grab (concat rust-re-ident "::")) 1 font-lock-type-face)

     ;; Lifetimes like `'foo`
     (,(concat "'" (rust-re-grab rust-re-ident) "[^']") 1 font-lock-variable-name-face)

     ;; Character constants, since they're not treated as strings
     ;; in order to have sufficient leeway to parse 'lifetime above.
     (,(rust-re-grab "'[^']'") 1 font-lock-string-face)
     (,(rust-re-grab "'\\\\[nrt]'") 1 font-lock-string-face)
     (,(rust-re-grab "'\\\\x[[:xdigit:]]\\{2\\}'") 1 font-lock-string-face)
     (,(rust-re-grab "'\\\\u[[:xdigit:]]\\{4\\}'") 1 font-lock-string-face)
     (,(rust-re-grab "'\\\\U[[:xdigit:]]\\{8\\}'") 1 font-lock-string-face)

     ;; CamelCase Means Type Or Constructor
     (,(rust-re-grabword rust-re-CamelCase) 1 font-lock-type-face)
     )

   ;; Item definitions
   (mapcar #'(lambda (x)
               (list (rust-re-item-def (car x))
                     1 (cdr x)))
           '(("enum" . font-lock-type-face)
             ("struct" . font-lock-type-face)
             ("type" . font-lock-type-face)
             ("mod" . font-lock-type-face)
             ("use" . font-lock-type-face)
             ("fn" . font-lock-function-name-face)
             ("static" . font-lock-constant-face)))))

(defun rust-fill-prefix-for-comment-start (line-start)
  "Determine what to use for `fill-prefix' based on what is at the beginning of a line."
  (let ((result
         ;; Replace /* with same number of spaces
         (replace-regexp-in-string
          "\\(?:/\\*+\\)[!*]"
          (lambda (s)
            ;; We want the * to line up with the first * of the comment start
            (concat (make-string (- (length s) 2) ?\x20) "*"))
          line-start)))
    ;; Make sure we've got at least one space at the end
    (if (not (= (aref result (- (length result) 1)) ?\x20))
        (setq result (concat result " ")))
    result))

(defun rust-in-comment-paragraph (body)
  ;; We might move the point to fill the next comment, but we don't want it
  ;; seeming to jump around on the user
  (save-excursion
    ;; If we're outside of a comment, with only whitespace and then a comment
    ;; in front, jump to the comment and prepare to fill it.
    (when (not (nth 4 (syntax-ppss)))
      (beginning-of-line)
      (when (looking-at (concat "[[:space:]\n]*" comment-start-skip))
        (goto-char (match-end 0))))

    ;; We need this when we're moving the point around and then checking syntax
    ;; while doing paragraph fills, because the cache it uses isn't always
    ;; invalidated during this.
    (syntax-ppss-flush-cache 1)
    ;; If we're at the beginning of a comment paragraph with nothing but
    ;; whitespace til the next line, jump to the next line so that we use the
    ;; existing prefix to figure out what the new prefix should be, rather than
    ;; inferring it from the comment start.
    (let ((next-bol (line-beginning-position 2)))
      (while (save-excursion
               (end-of-line)
               (syntax-ppss-flush-cache 1)
               (and (nth 4 (syntax-ppss))
                    (save-excursion
                      (beginning-of-line)
                      (looking-at paragraph-start))
                    (looking-at "[[:space:]]*$")
                    (nth 4 (syntax-ppss next-bol))))
        (goto-char next-bol)))

    (syntax-ppss-flush-cache 1)
    ;; If we're on the last line of a multiline-style comment that started
    ;; above, back up one line so we don't mistake the * of the */ that ends
    ;; the comment for a prefix.
    (when (save-excursion
            (and (nth 4 (syntax-ppss (line-beginning-position 1)))
                 (looking-at "[[:space:]]*\\*/")))
      (goto-char (line-end-position 0)))
    (funcall body)))

(defun rust-with-comment-fill-prefix (body)
  (let*
      ((line-string (buffer-substring-no-properties
                     (line-beginning-position) (line-end-position)))
       (line-comment-start
        (when (nth 4 (syntax-ppss))
          (cond
           ;; If we're inside the comment and see a * prefix, use it
           ((string-match "^\\([[:space:]]*\\*+[[:space:]]*\\)"
                          line-string)
            (match-string 1 line-string))
           ;; If we're at the start of a comment, figure out what prefix
           ;; to use for the subsequent lines after it
           ((string-match (concat "[[:space:]]*" comment-start-skip) line-string)
            (rust-fill-prefix-for-comment-start
             (match-string 0 line-string))))))
       (fill-prefix
        (or line-comment-start
            fill-prefix)))
    (funcall body)))

(defun rust-find-fill-prefix ()
  (rust-with-comment-fill-prefix (lambda () fill-prefix)))

(defun rust-fill-paragraph (&rest args)
  "Special wrapping for `fill-paragraph' to handle multi-line comments with a * prefix on each line."
  (rust-in-comment-paragraph
   (lambda ()
     (rust-with-comment-fill-prefix
      (lambda ()
        (let
            ((fill-paragraph-function
              (if (not (eq fill-paragraph-function 'rust-fill-paragraph))
                  fill-paragraph-function))
             (fill-paragraph-handle-comment t))
          (apply 'fill-paragraph args)
          t))))))

(defun rust-do-auto-fill (&rest args)
  "Special wrapping for `do-auto-fill' to handle multi-line comments with a * prefix on each line."
  (rust-with-comment-fill-prefix
   (lambda ()
     (apply 'do-auto-fill args)
     t)))

(defun rust-fill-forward-paragraph (arg)
  ;; This is to work around some funny behavior when a paragraph separator is
  ;; at the very top of the file and there is a fill prefix.
  (let ((fill-prefix nil)) (forward-paragraph arg)))

(defun rust-comment-indent-new-line (&optional arg)
  (rust-with-comment-fill-prefix
   (lambda () (comment-indent-new-line arg))))

;;; Imenu support
(defvar rust-imenu-generic-expression
  (append (mapcar #'(lambda (x)
                      (list nil (rust-re-item-def x) 1))
                  '("enum" "struct" "type" "mod" "fn" "trait"))
          `(("Impl" ,(rust-re-item-def "impl") 1)))
  "Value for `imenu-generic-expression' in Rust mode.

Create a flat index of the item definitions in a Rust file.

Imenu will show all the enums, structs, etc. at the same level.
Implementations will be shown under the `Impl` subheading.  Use
idomenu (imenu with `ido-mode') for best mileage.")

;;; Defun Motions

;;; Start of a Rust item
(defvar rust-top-item-beg-re
  (concat "^\\s-*\\(?:priv\\|pub\\)?\\s-*"
          (regexp-opt
           '("enum" "struct" "type" "mod" "use" "fn" "static" "impl"
             "extern" "impl" "static" "trait"))))

(defun rust-beginning-of-defun (&optional arg)
  "Move backward to the beginning of the current defun.

With ARG, move backward multiple defuns.  Negative ARG means
move forward.

This is written mainly to be used as `beginning-of-defun-function' for Rust.
Don't move to the beginning of the line. `beginning-of-defun',
which calls this, does that afterwards."
  (interactive "p")
  (re-search-backward (concat "^\\(" rust-top-item-beg-re "\\)\\b")
                      nil 'move (or arg 1)))

(defun rust-end-of-defun ()
  "Move forward to the next end of defun.

With argument, do it that many times.
Negative argument -N means move back to Nth preceding end of defun.

Assume that this is called after beginning-of-defun. So point is
at the beginning of the defun body.

This is written mainly to be used as `end-of-defun-function' for Rust."
  (interactive "p")
  ;; Find the opening brace
  (re-search-forward "[{]" nil t)
  (goto-char (match-beginning 0))
  ;; Go to the closing brace
  (forward-sexp))

;; For compatibility with Emacs < 24, derive conditionally
(defalias 'rust-parent-mode
  (if (fboundp 'prog-mode) 'prog-mode 'fundamental-mode))


;;;###autoload
(define-derived-mode rust-mode rust-parent-mode "Rust"
  "Major mode for Rust code."
  :group 'rust-mode
  :syntax-table rust-mode-syntax-table

  ;; Indentation
  (setq-local indent-line-function 'rust-mode-indent-line)

  ;; Fonts
  (setq-local font-lock-defaults '(rust-mode-font-lock-keywords nil nil nil nil))

  ;; Misc
  (setq-local comment-start "// ")
  (setq-local comment-end   "")
  (setq-local indent-tabs-mode nil)

  ;; Allow paragraph fills for comments
  (setq-local comment-start-skip "\\(?://[/!]*\\|/\\*[*!]?\\)[[:space:]]*")
  (setq-local paragraph-start
       (concat "[[:space:]]*\\(?:" comment-start-skip "\\|\\*/?[[:space:]]*\\|\\)$"))
  (setq-local paragraph-separate paragraph-start)
  (setq-local normal-auto-fill-function 'rust-do-auto-fill)
  (setq-local fill-paragraph-function 'rust-fill-paragraph)
  (setq-local fill-forward-paragraph-function 'rust-fill-forward-paragraph)
  (setq-local adaptive-fill-function 'rust-find-fill-prefix)
  (setq-local comment-multi-line t)
  (setq-local comment-line-break-function 'rust-comment-indent-new-line)
  (setq-local imenu-generic-expression rust-imenu-generic-expression)
  (setq-local beginning-of-defun-function 'rust-beginning-of-defun)
  (setq-local end-of-defun-function 'rust-end-of-defun))

;;;###autoload
(add-to-list 'auto-mode-alist '("\\.rs\\'" . rust-mode))

(defun rust-mode-reload ()
  (interactive)
  (unload-feature 'rust-mode)
  (require 'rust-mode)
  (rust-mode))

;; Issue #6887: Rather than inheriting the 'gnu compilation error
;; regexp (which is broken on a few edge cases), add our own 'rust
;; compilation error regexp and use it instead.
(defvar rustc-compilation-regexps
  (let ((file "\\([^\n]+\\)")
        (start-line "\\([0-9]+\\)")
        (start-col  "\\([0-9]+\\)")
        (end-line   "\\([0-9]+\\)")
        (end-col    "\\([0-9]+\\)")
        (error-or-warning "\\(?:[Ee]rror\\|\\([Ww]arning\\)\\)"))
    (let ((re (concat "^" file ":" start-line ":" start-col
                      ": " end-line ":" end-col
                      " \\(?:[Ee]rror\\|\\([Ww]arning\\)\\):")))
      (cons re '(1 (2 . 4) (3 . 5) (6)))))
  "Specifications for matching errors in rustc invocations.
See `compilation-error-regexp-alist for help on their format.")

(eval-after-load 'compile
  '(progn
     (add-to-list 'compilation-error-regexp-alist-alist
                  (cons 'rustc rustc-compilation-regexps))
     (add-to-list 'compilation-error-regexp-alist 'rustc)))

(provide 'rust-mode)

;;; rust-mode.el ends here