Fix syntax and highlighting for char literals

This uses syntax properties to make it so that emacs recognizes the
single quote, rather than the double quote, as the string delimiter
within character literals, while leaving the syntax unchanged elsewhere.

Author: MicahChalmer

rust-mode-tests.el

@@ -893,3 +893,9 @@ list of substrings of `STR' each followed by its face."
    "/* #[foo] */"
    '("/* " font-lock-comment-delimiter-face
      "#[foo] */" font-lock-comment-face)))
+
+(ert-deftest font-lock-double-quote-character-literal ()
+  (rust-test-font-lock
+   "'\"'; let"
+   '("'\"'" font-lock-string-face
+     "let" font-lock-keyword-face)))

rust-mode.el

@@ -44,6 +44,13 @@
 
     table))
 
+(defvar rust-mode-character-literal-syntax-table
+  (let ((table (make-syntax-table rust-mode-syntax-table)))
+    (modify-syntax-entry ?' "\"" table)
+    (modify-syntax-entry ?\" "_" table)
+
+    table))
+
 (defgroup rust-mode nil
   "Support for Rust code."
   :link '(url-link "http://www.rust-lang.org/")
@@ -259,14 +266,6 @@
      ;; 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)
      )
@@ -439,12 +438,19 @@ 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")
+  (interactive)
   ;; Find the opening brace
-  (re-search-forward "[{]" nil t)
-  (goto-char (match-beginning 0))
-  ;; Go to the closing brace
-  (forward-sexp))
+  (if (re-search-forward "[{]" nil t)
+      (progn
+        (goto-char (match-beginning 0))
+        ;; Go to the closing brace
+        (condition-case err
+            (forward-sexp)
+          (scan-error
+           ;; The parentheses are unbalanced; instead of being unable to fontify, just jump to the end of the buffer
+           (goto-char (point-max)))))
+    ;; There is no opening brace, so consider the whole buffer to be one "defun"
+    (goto-char (point-max))))
 
 ;; For compatibility with Emacs < 24, derive conditionally
 (defalias 'rust-parent-mode
@@ -481,7 +487,34 @@ This is written mainly to be used as `end-of-defun-function' for Rust."
   (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))
+  (setq-local end-of-defun-function 'rust-end-of-defun)
+  (setq-local parse-sexp-lookup-properties t)
+  (add-hook 'syntax-propertize-extend-region-functions 'rust-syntax-propertize-extend-region)
+  (setq-local syntax-propertize-function 'rust-syntax-propertize))
+
+(defun rust-syntax-propertize-extend-region (start end)
+  (save-excursion
+    (goto-char start)
+    (beginning-of-defun)
+    (cons
+     (point)
+     (progn
+       (goto-char end)
+       (end-of-defun)
+       (point)))))
+
+(defun rust-syntax-propertize (start end)
+  ;; Find character literals and make the syntax table recognize the single quote as the string delimiter
+  (dolist (char-lit-re
+           '("'[^']'"
+             "'\\\\['nrt]'"
+             "'\\\\x[[:xdigit:]]\\{2\\}'"
+             "'\\\\u[[:xdigit:]]\\{4\\}'"
+             "'\\\\U[[:xdigit:]]\\{8\\}'"))
+    (save-excursion
+      (goto-char start)
+      (while (re-search-forward char-lit-re end t)
+        (put-text-property (match-beginning 0) (match-end 0) 'syntax-table rust-mode-character-literal-syntax-table)))))
 
 ;;;###autoload
 (add-to-list 'auto-mode-alist '("\\.rs\\'" . rust-mode))