nix-mode: set syntax and font properties for multiline strings

misc/emacs/nix-mode.el

@@ -8,6 +8,20 @@
 
 ;;; 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\\_>"
@@ -26,7 +40,8 @@
     ("<[a-zA-Z0-9._\\+-]+\\(/[a-zA-Z0-9._\\+-]+\\)*>"
      . font-lock-constant-face)
     ("[a-zA-Z0-9._\\+-]*\\(/[a-zA-Z0-9._\\+-]+\\)+"
-     . font-lock-constant-face))
+     . font-lock-constant-face)
+    (nix-syntax-match-antiquote 0 font-lock-preprocessor-face t))
   "Font lock keywords for nix.")
 
 (defvar nix-mode-syntax-table
@@ -38,6 +53,67 @@
     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)
@@ -69,7 +145,13 @@ The hook `nix-mode-hook' is run when Nix mode is started.
   (set-syntax-table nix-mode-syntax-table)
 
   ;; Font lock support.
-  (setq font-lock-defaults '(nix-font-lock-keywords nil nil nil nil))
+  (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)