Improve flyspell support

+ Make flyspell more selective about what to scan in markdown buffers.
+ Don't mark duplicates when proseline or langtool are present.
+ Add set-flyspell-predicate! for seeing mode-specific word predicates.

modules/tools/flyspell/autoload.el

@@ -0,0 +1,16 @@
+;;; tools/flyspell/autoload.el -*- lexical-binding: t; -*-
+
+(defvar +flyspell--predicate-alist nil
+  "TODO")
+
+;;;###autodef
+(defun set-flyspell-predicate! (modes predicate)
+  "TODO"
+  (dolist (mode (doom-enlist modes) +flyspell--predicate-alist)
+    (add-to-list '+flyspell--predicate-alist (cons mode predicate))))
+
+;;;###autoload
+(defun +flyspell|init-predicate ()
+  "TODO"
+  (when-let* ((pred (assq major-mode +flyspell--predicate-alist)))
+    (setq-local flyspell-generic-check-word-predicate (cdr pred))))

modules/tools/flyspell/config.el

@@ -47,13 +47,26 @@ Since spellchecking can be slow in some buffers, this can be disabled with:
 
 
 ;; `flyspell' (built-in)
-(setq flyspell-issue-welcome-flag nil)
+(progn
+  (setq flyspell-issue-welcome-flag nil)
 
-(defun +flyspell|immediately ()
-  "Spellcheck the buffer when `flyspell-mode' is enabled."
-  (when (and flyspell-mode +flyspell-immediately)
-    (flyspell-buffer)))
-(add-hook 'flyspell-mode-hook #'+flyspell|immediately)
+  (defun +flyspell|inhibit-duplicate-detection-maybe ()
+    "Don't mark duplicates when style/grammar linters are present.
+e.g. proselint and langtool."
+    (when (or (executable-find "proselint")
+              (featurep 'langtool))
+      (setq-local flyspell-mark-duplications-flag nil)))
+  (add-hook 'flyspell-mode-hook #'+flyspell|inhibit-duplicate-detection-maybe)
+
+  (defun +flyspell|immediately ()
+    "Spellcheck the buffer when `flyspell-mode' is enabled."
+    (when (and flyspell-mode +flyspell-immediately)
+      (flyspell-buffer)))
+  (add-hook 'flyspell-mode-hook #'+flyspell|immediately)
+
+  ;; Ensure mode-local predicates declared with `set-flyspell-predicate!' are
+  ;; used in their respective major modes.
+  (add-hook 'flyspell-mode-hook #'+flyspell|init-predicate))
 
 
 (def-package! flyspell-correct