emacs-删除掉空的agenda-block
在使用org-agenda-custom-commands时，有时会创建agenda-block。如果你是用的org-ql-block，那么在未query到结果时会为空；但如果你用的org-agenda，则可能会因为一些原因留有空的block。
根据reddit的一个帖子，以下函数可以在某个block有小于2行不以空格开头时，删除掉这个block。
（标题为一行，分割线上的空格为一行）
(defun org-agenda-delete-empty-blocks ()
"Remove empty agenda blocks.
A block is identified as empty if there are fewer than 2
non-empty lines in the block (excluding the line with
`org-agenda-block-separator' characters)."
(when org-agenda-compact-blocks
(user-error "Cannot delete empty compact blocks"))
(setq buffer-read-only nil)
(save-excursion
(goto-char (point-min))
(let* ((blank-line-re "^\\s-*$")
(content-line-count (if (looking-at-p blank-line-re) 0 1))
(start-pos (point))
(block-re (format "%c\\{10,\\}" org-agenda-block-separator)))
(while (and (not (eobp)) (forward-line))
(cond
((looking-at-p block-re)
(when (< content-line-count 2)
(delete-region start-pos (1+ (pos-bol))))
(setq start-pos (point))
(forward-line)
(setq content-line-count (if (looking-at-p blank-line-re) 0 1)))
((not (looking-at-p blank-line-re))
(setq content-line-count (1+ content-line-count)))))
(when (< content-line-count 2)
(delete-region start-pos (point-max)))
;; 上面这个函数是针对agenda-block在最下方写的，会让agenda中更改todo状态后的文本消失。
(goto-char (point-min))
;; The above strategy can leave a separator line at the beginning
;; of the buffer.
(when (looking-at-p block-re)
(delete-region (point) (1+ (pos-eol))))))
(setq buffer-read-only t))
(add-hook 'org-agenda-finalize-hook #'org-agenda-delete-empty-blocks)
当然，我们也可以自定义 blank-line-re 的值，用来匹配其他文本内容。