.emacs.d/init/basics/buffers.el

;;; buffers.el --- Default settings for buffers. -*- lexical-binding: t; -*-

;; Time-stamp: <2019-11-25T20:52:35+00:00>

;;; Commentary:
;; * Setup scratch buffer.
;; * Set fill-column.
;; * Define which buffers should be ignored.
;; * Enable auto-fill-mode.

;;; Code:

(use-package emacs
  :ensure nil

  :custom
  (initial-scratch-message nil)        ; Make scratch buffer empty,
  (initial-major-mode 'markdown-mode)  ; and select mode.

  :config
  (defvar my/skippable-buffers '("^\\*" "^magit[:-]")
    "Buffer names ignored by `next-buffer' and `previous-buffer'.")
  (defvar my/never-skippable-buffers '("^\\*scratch\\*$" "^\\*Easy-hugo\\*$")
    "Buffer names never ignored by `next-buffer' and `previous-buffer'.")

  (defun my/buffer-predicate (buffer)
    "Returns nil if buffer-name matches expression in `my/skippable-buffers'."
    (catch 'return
      ;; Return t if buffer-name is on never-skippable list.
      (dolist (expression my/never-skippable-buffers)
        (if (string-match expression (buffer-name buffer))
            (throw 'return t)
          ))
      ;; Return nil if buffer-name is on skippable list.
      (dolist (expression my/skippable-buffers)
        (if (string-match expression (buffer-name buffer))
            (throw 'return nil)
          ))
      t))

  (set-frame-parameter nil 'buffer-predicate 'my/buffer-predicate)
  )

;; Show and select buffers.
(use-package bs
  :bind
  ("C-x C-b" . bs-show)
  )

;; Delete old buffers.
;; https://www.emacswiki.org/emacs/CleanBufferList
(use-package midnight
  :ensure nil                           ; Builtin.
  :defer 10

  :init
  (setq midnight-delay 30                     ; 30 seconds after “midnight”.
        midnight-period (* 2 60 60))          ; Clean every 2 hours.

  :custom
  (clean-buffer-list-delay-general 1)         ; Clean normal bufs after 1d.
  (clean-buffer-list-delay-special (* 30 60)) ; Clean special bufs after 30m.

  :config
  (setq clean-buffer-list-kill-regexps        ; Add these to special buffers.
        (nconc clean-buffer-list-kill-regexps
               '("\\`magit-?.*:"
                 "\\.log\\'"
                 "\\`\\*rdm\\*\\'"
                 "\\`\\*Backtrace\\*\\'"
                 "\\`Pfuture-Callback")))
  (midnight-mode t)
  )

(provide 'basics/buffers)
;;; buffers.el ends here