packages.el

  (defvar-local prose-proselint-enabled nil
    "Buffer local proselint enabled status")

  (defun prose-proselint-enabled-p ()
    "Workaround for proselint flycheck checker predicate"
    prose-proselint-enabled)

  (flycheck-define-checker proselint
    "A linter for prose."
    :command ("proselint" source-inplace)
    :error-patterns
    ((warning line-start (file-name) ":" line ":" column ": "
              (id (one-or-more (not (any " "))))
              (message (one-or-more not-newline)
                       (zero-or-more "\n" (any " ") (one-or-more not-newline)))
              line-end))
    :predicate prose-proselint-enabled-p)
    ;; :modes (text-mode markdown-mode gfm-mode))
  (add-to-list 'flycheck-checkers 'proselint)

  (defun prose-reset-proselint-next-checkers ()
    "Adds the usual mode checkers as next checkers to the proselint checker"
    ;; Reset the proselint next-checkers prop to nil
    (setf (flycheck-checker-get 'proselint 'next-checkers) nil)
    ;; Add the regular mode and predicate checkers for this buffer
    (dolist (checker (flycheck-possibly-suitable-checkers))
      (unless (eq checker 'proselint)
        (flycheck-add-next-checker 'proselint (cons t checker) t))))
  (add-hook 'flycheck-before-syntax-check-hook 'prose-reset-proselint-next-checkers)