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+;;; nix-mode.el --- Major mode for editing Nix expressions
+
+;; Author: Eelco Dolstra
+;; URL: https://github.com/NixOS/nix/tree/master/misc/emacs
+;; Version: 1.0
+
+;;; Commentary:
+
+;;; Code:
+
+(defun nix-syntax-match-antiquote (limit)
+  (let ((pos (next-single-char-property-change (point) 'nix-syntax-antiquote
+                                               nil limit)))
+    (when (and pos (> pos (point)))
+      (goto-char pos)
+      (let ((char (char-after pos)))
+        (pcase char
+          (`?$
+           (forward-char 2))
+          (`?}
+           (forward-char 1)))
+        (set-match-data (list pos (point)))
+        t))))
+
+(defconst nix-font-lock-keywords
+  '("\\_<if\\_>" "\\_<then\\_>" "\\_<else\\_>" "\\_<assert\\_>" "\\_<with\\_>"
+    "\\_<let\\_>" "\\_<in\\_>" "\\_<rec\\_>" "\\_<inherit\\_>" "\\_<or\\_>"
+    ("\\_<true\\_>" . font-lock-builtin-face)
+    ("\\_<false\\_>" . font-lock-builtin-face)
+    ("\\_<null\\_>" . font-lock-builtin-face)
+    ("\\_<import\\_>" . font-lock-builtin-face)
+    ("\\_<derivation\\_>" . font-lock-builtin-face)
+    ("\\_<baseNameOf\\_>" . font-lock-builtin-face)
+    ("\\_<toString\\_>" . font-lock-builtin-face)
+    ("\\_<isNull\\_>" . font-lock-builtin-face)
+    ("[a-zA-Z][a-zA-Z0-9\\+-\\.]*:[a-zA-Z0-9%/\\?:@&=\\+\\$,_\\.!~\\*'-]+"
+     . font-lock-constant-face)
+    ("\\<\\([a-zA-Z_][a-zA-Z0-9_'\-\.]*\\)[ \t]*="
+     (1 font-lock-variable-name-face nil nil))
+    ("<[a-zA-Z0-9._\\+-]+\\(/[a-zA-Z0-9._\\+-]+\\)*>"
+     . font-lock-constant-face)
+    ("[a-zA-Z0-9._\\+-]*\\(/[a-zA-Z0-9._\\+-]+\\)+"
+     . font-lock-constant-face)
+    (nix-syntax-match-antiquote 0 font-lock-preprocessor-face t))
+  "Font lock keywords for nix.")
+
+(defvar nix-mode-syntax-table
+  (let ((table (make-syntax-table)))
+    (modify-syntax-entry ?/ ". 14" table)
+    (modify-syntax-entry ?* ". 23" table)
+    (modify-syntax-entry ?# "< b" table)
+    (modify-syntax-entry ?\n "> b" table)
+    table)
+  "Syntax table for Nix mode.")
+
+(defun nix-syntax-propertize-escaped-antiquote ()
+  "Set syntax properies for escaped antiquote marks."
+  nil)
+
+(defun nix-syntax-propertize-multiline-string ()
+  "Set syntax properies for multiline string delimiters."
+  (let* ((start (match-beginning 0))
+         (end (match-end 0))
+         (context (save-excursion (save-match-data (syntax-ppss start))))
+         (string-type (nth 3 context)))
+    (pcase string-type
+      (`t
+       ;; inside a multiline string
+       ;; ending multi-line string delimiter
+       (put-text-property (1- end) end
+                          'syntax-table (string-to-syntax "|")))
+      (`nil
+       ;; beginning multi-line string delimiter
+       (put-text-property start (1+ start)
+                          'syntax-table (string-to-syntax "|"))))))
+
+(defun nix-syntax-propertize-antiquote ()
+  "Set syntax properties for antiquote marks."
+  (let* ((start (match-beginning 0)))
+    (put-text-property start (1+ start)
+                       'syntax-table (string-to-syntax "|"))
+    (put-text-property start (+ start 2)
+                       'nix-syntax-antiquote t)))
+
+(defun nix-syntax-propertize-close-brace ()
+  "Set syntax properties for close braces.
+If a close brace `}' ends an antiquote, the next character begins a string."
+  (let* ((start (match-beginning 0))
+         (end (match-end 0))
+         (context (save-excursion (save-match-data (syntax-ppss start))))
+         (open (nth 1 context)))
+    (when open ;; a corresponding open-brace was found
+      (let* ((antiquote (get-text-property open 'nix-syntax-antiquote)))
+        (when antiquote
+          (put-text-property (+ start 1) (+ start 2)
+                             'syntax-table (string-to-syntax "|"))
+          (put-text-property start (1+ start)
+                             'nix-syntax-antiquote t))))))
+
+(defun nix-syntax-propertize (start end)
+  "Special syntax properties for Nix."
+  ;; search for multi-line string delimiters
+  (goto-char start)
+  (remove-text-properties start end '(syntax-table nil nix-syntax-antiquote nil))
+  (funcall
+   (syntax-propertize-rules
+    ("''\\${"
+     (0 (ignore (nix-syntax-propertize-escaped-antiquote))))
+    ("''"
+     (0 (ignore (nix-syntax-propertize-multiline-string))))
+    ("\\${"
+     (0 (ignore (nix-syntax-propertize-antiquote))))
+    ("}"
+     (0 (ignore (nix-syntax-propertize-close-brace)))))
+   start end))
+
+(defun nix-indent-line ()
+  "Indent current line in a Nix expression."
+  (interactive)
+  (indent-relative-maybe))
+
+
+;;;###autoload
+(define-derived-mode nix-mode prog-mode "Nix"
+  "Major mode for editing Nix expressions.
+
+The following commands may be useful:
+
+  '\\[newline-and-indent]'
+    Insert a newline and move the cursor to align with the previous
+    non-empty line.
+
+  '\\[fill-paragraph]'
+    Refill a paragraph so that all lines are at most `fill-column'
+    lines long.  This should do the right thing for comments beginning
+    with `#'.  However, this command doesn't work properly yet if the
+    comment is adjacent to code (i.e., no intervening empty lines).
+    In that case, select the text to be refilled and use
+    `\\[fill-region]' instead.
+
+The hook `nix-mode-hook' is run when Nix mode is started.
+
+\\{nix-mode-map}
+"
+  (set-syntax-table nix-mode-syntax-table)
+
+  ;; Font lock support.
+  (setq-local font-lock-defaults '(nix-font-lock-keywords nil nil nil nil))
+
+  ;; Special syntax properties for Nix
+  (setq-local syntax-propertize-function 'nix-syntax-propertize)
+
+  ;; Look at text properties when parsing
+  (setq-local parse-sexp-lookup-properties t)
+
+  ;; Automatic indentation [C-j].
+  (set (make-local-variable 'indent-line-function) 'nix-indent-line)
+
+  ;; Indenting of comments.
+  (set (make-local-variable 'comment-start) "# ")
+  (set (make-local-variable 'comment-end) "")
+  (set (make-local-variable 'comment-start-skip) "\\(^\\|\\s-\\);?#+ *")
+
+  ;; Filling of comments.
+  (set (make-local-variable 'adaptive-fill-mode) t)
+  (set (make-local-variable 'paragraph-start) "[ \t]*\\(#+[ \t]*\\)?$")
+  (set (make-local-variable 'paragraph-separate) paragraph-start))
+
+
+;;;###autoload
+(progn
+  (add-to-list 'auto-mode-alist '("\\.nix\\'" . nix-mode))
+  (add-to-list 'auto-mode-alist '("\\.nix.in\\'" . nix-mode)))
+
+(provide 'nix-mode)
+
+;;; nix-mode.el ends here