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

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

;; Time-stamp: <2020-02-11T23:30:47+0100>

;;; 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)

  (defun my/truncate-lines ()
    "Truncate lines instead of wrapping them."
    (setq-local truncate-lines t))

  :bind
  ;; Switch buffers.
  ("M-<left>"      . previous-buffer)
  ("M-<right>"     . next-buffer)

  :hook
  (prog-mode . my/truncate-lines)
  (conf-mode . my/truncate-lines)
  )

;; 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
  :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)
  )

(use-package window-purpose
  :pin melpa  ; We need > 1.7 <https://github.com/bmag/emacs-purpose/issues/158>
  :defer nil

  :config
  (purpose-mode)
  (add-to-list 'purpose-user-mode-purposes '(c++-mode . cpp))
  (add-to-list 'purpose-user-mode-purposes '(emacs-lisp-mode . elisp))
  (add-to-list 'purpose-user-mode-purposes '(ebuild-mode . ebuild))
  (add-to-list 'purpose-user-mode-purposes '(adoc-mode . adoc))
  (add-to-list 'purpose-user-mode-purposes '(markdown-mode . md))
  (add-to-list 'purpose-user-mode-purposes '(gfm-mode . md))
  (add-to-list 'purpose-user-mode-purposes '(Man-mode . help-buf))
  (add-to-list 'purpose-user-mode-purposes '(help-mode . help-buf))
  (add-to-list 'purpose-user-mode-purposes '(info-mode . help-buf))
  (add-to-list 'purpose-user-mode-purposes '(compilation-mode . compile))

  (add-to-list 'purpose-special-action-sequences
               '(help-buf purpose-display-reuse-window-buffer))
  (purpose-compile-user-configuration)

  (require 'window-purpose-x)
  (purpose-x-magit-single-on)        ; All Magit buffers have the same purpose.
  (purpose-x-kill-setup)             ; Replace killed buffers with same purpose.

  :bind
  ("<f2>" . purpose-toggle-window-purpose-dedicated)
  ("C-<f2>" . purpose-toggle-window-buffer-dedicated)
  ("M-<f2>" . purpose-load-window-layout)
  )

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