Emacs selection by indentation - emacs

Question

In Sublime Text one can select a block of code based on indentation:
(Selection -> Expand Selection to Indentation)
For example in the following block of code and cursor at position being
marked here:
<header>
<nav>
<ul>
<li id='link-main'><a href='#'>Main site</a></li>
<li class='stupid'><a href='#'>About Us</a></li>
<li class='stupid'>History</li>
<CURSOR_HERE>
<div>
<div>
</div>
</div>
<li>Contact</li>
</ul>
</nav>
</header>
This will result in this selection (marked by <SELECTION> and </SELECTION>)
<header>
<nav>
<ul>
<SELECTION><li id='link-main'><a href='#'>Main site</a></li>
<li class='stupid'><a href='#'>About Us</a></li>
<li class='stupid'>History</li>
<div>
<div>
</div>
</div>
<li>Contact</li></SELECTION>
</ul>
</nav>
</header>
How can I achieve the same thing using emacs?

Answer 1

If you use Evil, here's an evil plugin evil-indent-textobject can select (or yank/delete) a block based of indentation.

Answer 2

I don't know about indentation-based selection, but expand region does semantic expansion:
Expand region increases the selected region by semantic units. Just keep pressing the key until it selects what you want.
Expand region is available on MELPA.

Answer 3

(defun ar-backward-indent ()
"Go backward same or deeper levels of indentation. "
(interactive)
(let ((orig (point))
(indent (progn (back-to-indentation) (current-column)))
(last (point)))
(while (and (not (bobp))(forward-line -1) (progn (back-to-indentation) (<= indent (current-indentation))))
(setq last (point)))
(goto-char last)))
(defun ar-forward-indent ()
"Go backward same or deeper levels of indentation. "
(interactive)
(let ((indent (progn (back-to-indentation) (current-column)))
last)
(while
(and (not (eobp)) (forward-line 1) (progn (back-to-indentation) (<= indent (current-indentation))))
(setq last (line-end-position)))
(goto-char last)))
(defun ar-mark-indent-level ()
"Mark lines around point where indentation is equal or deeper. "
(interactive)
(let ((orig (point)))
(ar-backward-indent)
(push-mark (point) t)
(goto-char orig)
(ar-forward-indent)))
Source: https://github.com/andreas-roehler/subroutines

Answer 4

First we have to check if point is on a line with 0 indentation, if it is select whole buffer.
If point is on a line with some indentation, select all lines which have same or less indentation.
(defun expand-to-indentation ()
"Select surrounding lines with current indentation."
(interactive)
(let ((indentation (current-indentation)))
(if (= indentation 0)
(mark-whole-buffer)
(while (<= indentation (current-indentation))
(forward-line -1))
(forward-line 1)
(push-mark (point) nil t)
(while (<= indentation (current-indentation))
(forward-line 1))
(backward-char))))
You can call this function interactively or you can bind it to any key.

Answer 5

Based on #ChillarAnand 's answer, I'm using below for myself:
(defun mark-current-indentation (&optional ARG)
"Select surrounding lines with current indentation.
if ARG is 'C-u', mark forward; if ARG is 'C-u C-u', mark backward."
(interactive "P")
(let ((is-forward (not (equal ARG '(16))))
(is-backward (not (equal ARG '(4))))
(indentation (if (not (current-line-empty-p))
(current-indentation)
(skip-chars-forward "\s\t\n")
(current-indentation))))
(if (= indentation 0)
(mark-whole-buffer)
(if (not is-forward) (push-mark (point) nil t))
(while (and (not (bobp)) is-backward
(or (current-line-empty-p) (<= indentation (current-indentation))))
(forward-line -1))
(if is-backward (forward-line 1) (move-beginning-of-line nil))
(if (not (use-region-p)) (push-mark (point) nil t))
(while (and (not (eobp)) is-forward
(or (current-line-empty-p) (<= indentation (current-indentation))))
(forward-line 1))
(if is-forward (backward-char)))))