Only set font-lock-defaults once to prevent clobbering user keywords

Closes GH-222.

CHANGES.md

@@ -46,9 +46,12 @@
         ([GH-276][])
     -   Don't set `markdown-code-face` background color at package
         load time.  ([GH-273][])
+    -   Don't clobber user specified font-lock keywords when toggling
+        features.  ([GH-222][])
 
   [gh-171]: https://github.com/jrblevin/markdown-mode/issues/171
   [gh-216]: https://github.com/jrblevin/markdown-mode/issues/216
+  [gh-222]: https://github.com/jrblevin/markdown-mode/issues/222
   [gh-227]: https://github.com/jrblevin/markdown-mode/issues/227
   [gh-229]: https://github.com/jrblevin/markdown-mode/pull/229
   [gh-238]: https://github.com/jrblevin/markdown-mode/issues/238

markdown-mode.el

@@ -2913,11 +2913,6 @@ Depending on your font, some reasonable choices are:
     (markdown-match-wiki-link . ((0 markdown-link-face prepend))))
   "Syntax highlighting for Markdown files.")
 
-(defvar markdown-mode-font-lock-keywords nil
-  "Default highlighting expressions for Markdown mode.
-This variable is defined as a buffer-local variable for dynamic
-extension support.")
-
 ;; Footnotes
 (defvar markdown-footnote-counter 0
   "Counter for footnote numbers.")
@@ -8649,20 +8644,9 @@ or span."
   "Check settings, update font-lock keywords and hooks, and re-fontify buffer."
   (interactive)
   (when (member major-mode '(markdown-mode gfm-mode))
-    ;; Update font lock keywords with extensions
-    (setq markdown-mode-font-lock-keywords
-          (append
-           (markdown-mode-font-lock-keywords-math)
-           markdown-mode-font-lock-keywords-basic))
-    ;; Update font lock defaults
-    (setq font-lock-defaults
-          '(markdown-mode-font-lock-keywords
-            nil nil nil nil
-            (font-lock-syntactic-face-function . markdown-syntactic-face)))
     ;; Refontify buffer
     (when (and font-lock-mode (fboundp 'font-lock-refresh-defaults))
       (font-lock-refresh-defaults))
-
     ;; Add or remove hooks related to extensions
     (markdown-setup-wiki-link-hooks)))
 
@@ -8754,10 +8738,6 @@ if ARG is omitted or nil."
     (message "markdown-mode math support disabled"))
   (markdown-reload-extensions))
 
-(defun markdown-mode-font-lock-keywords-math ()
-  "Return math font lock keywords if support is enabled."
-  '())
-
 
 ;;; GFM Checkboxes ============================================================
 
@@ -9789,7 +9769,6 @@ spaces, or alternatively a TAB should be used as the separator."
             #'markdown-font-lock-extend-region-function t t)
   (setq-local syntax-propertize-function #'markdown-syntax-propertize)
   ;; Font lock.
-  (setq-local markdown-mode-font-lock-keywords nil)
   (setq-local font-lock-defaults nil)
   (setq-local font-lock-multiline t)
   (setq-local font-lock-extra-managed-props
@@ -9798,8 +9777,14 @@ spaces, or alternatively a TAB should be used as the separator."
   (if markdown-hide-markup
       (add-to-invisibility-spec 'markdown-markup)
     (remove-from-invisibility-spec 'markdown-markup))
-  ;; Reload extensions
-  (markdown-reload-extensions)
+  (setq font-lock-defaults
+        '(markdown-mode-font-lock-keywords-basic
+          nil nil nil nil
+          (font-lock-syntactic-face-function . markdown-syntactic-face)))
+  ;; Wiki links
+  (markdown-setup-wiki-link-hooks)
+  ;; Math mode
+  (when markdown-enable-math (markdown-toggle-math t))
   ;; Add a buffer-local hook to reload after file-local variables are read
   (add-hook 'hack-local-variables-hook #'markdown-handle-local-variables nil t)
   ;; For imenu support

tests/markdown-test.el

@@ -4979,6 +4979,25 @@ This includes preserving whitespace after the pipe."
       (should (member (car markdown-mode-font-lock-keywords-math)
                       (cadr font-lock-keywords))))))
 
+(ert-deftest test-markdown-math/preserve-user-keywords ()
+  "Test preserving user-specified font-lock keywords."
+  (let ((user-keyword '("\\<\\(FIXME\\):" 1 font-lock-warning-face t)))
+    ;; Add user font-lock keyword using `font-lock-add-keywords'.
+    (font-lock-add-keywords 'markdown-mode (list user-keyword))
+    ;; Visit a file using `markdown-mode'.
+    (markdown-test-file "math.text"
+      ;; User keyword should be present initially.
+      (should (member user-keyword (cadr font-lock-keywords)))
+      ;; User keyword should persist after calling `markdown-reload-extensions'.
+      (markdown-reload-extensions)
+      (should (member user-keyword (cadr font-lock-keywords))))
+    ;; Remove the user keyword using `font-lock-remove-keywords'.
+    (font-lock-remove-keywords 'markdown-mode (list user-keyword))
+    ;; Visit a file using `markdown-mode'.
+    (markdown-test-file "inline.text"
+      ;; User keyword should not be present after removal.
+      (should-not (member user-keyword (cadr font-lock-keywords))))))
+
 (ert-deftest test-markdown-math/font-lock ()
   "Test markdown math mode."
   (let ((markdown-enable-math t))