:PROPERTIES:
:ID:       334a4188-93e6-4378-b22d-b0c302fc26a1
:END:
#+title: Flycheck
#+filetags: emacs-load

# SPDX-FileCopyrightText: 2022 Richard Brežák <richard@brezak.sk>
#
# SPDX-License-Identifier: LGPL-3.0-or-later

* Flycheck Posframe

Display flycheck messages in a posframe.

#+begin_src emacs-lisp :noweb yes
  (use-package flycheck-posframe
    :straight t
    :config
    (setq flycheck-posframe-position 'frame-bottom-right-corner)
    <<flycheck-display-errors-delay>>
    <<lsp-ui-sideline-show-diagnostics>>
    :hook (flycheck-mode . flycheck-posframe-mode))
#+end_src

Flycheck calls ~flycheck-display-errors-function~ every ~flycheck-display-errors-delay~.

#+name: flycheck-display-errors-delay
#+begin_src emacs-lisp
  (setq flycheck-display-errors-delay 0.1)
#+end_src

Since we get errors and such in a posframe, we don't need them in the sideline.

#+name: lsp-ui-sideline-show-diagnostics
#+begin_src emacs-lisp
  (setq lsp-ui-sideline-show-diagnostics nil)
#+end_src

Since flycheck recalls ~flycheck-display-errors-function~ on every point movement, it creates this really ugly flicker and also lags a bit, so if the diagnostic message didn't change, filter out the call.

#+name: flycheck-posframe-change-filter
#+begin_src emacs-lisp
  (defvar flycheck-posframe-last-error-list '())

  (advice-add
   'flycheck-posframe-hidehandler
   :override
   (lambda (info)
     (if (not (equal
                 (flycheck-overlay-errors-at (point))
                 flycheck-posframe-last-error-list))
         (progn
           (setq flycheck-posframe-last-error-list nil)
           t)
       nil))
   '((name . "flycheck-error-display-filter")))

  (advice-add
   'flycheck-posframe-show-posframe
   :before-while
   (lambda (diagnostic)
     (let ((last-list flycheck-posframe-last-error-list))
       (setq flycheck-posframe-last-error-list diagnostic)
       (if (equal diagnostic last-list) nil t)))
   '((name . "flycheck-error-display-filter")))
#+end_src