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;;; hl-line.el --- highlight the current line  -*- lexical-binding:t -*-
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;; Copyright (C) 1998, 2000-2019 Free Software Foundation, Inc.
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;; Author: Dave Love <fx@gnu.org>
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;; Maintainer: emacs-devel@gnu.org
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;; Created: 1998-09-13
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;; Keywords: faces, frames, emulations
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;; This file is part of GNU Emacs.

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;; GNU Emacs is free software: you can redistribute it and/or modify
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;; it under the terms of the GNU General Public License as published by
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;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.
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;; GNU Emacs is distributed in the hope that it will be useful,
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;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.

;; You should have received a copy of the GNU General Public License
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;; along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.
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;;; Commentary:

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;; Provides a local minor mode (toggled by M-x hl-line-mode) and
;; a global minor mode (toggled by M-x global-hl-line-mode) to
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;; highlight, on a suitable terminal, the line on which point is.  The
;; global mode highlights the current line in the selected window only
;; (except when the minibuffer window is selected).  This was
;; implemented to satisfy a request for a feature of Lesser Editors.
;; The local mode is sticky: it highlights the line about the buffer's
;; point even if the buffer's window is not selected.  Caveat: the
;; buffer's point might be different from the point of a non-selected
;; window.  Set the variable `hl-line-sticky-flag' to nil to make the
;; local mode behave like the global mode.

;; You probably don't really want to use the global mode; if the
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;; cursor is difficult to spot, try changing its color, relying on
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;; `blink-cursor-mode' or both.  The hookery used might affect
;; response noticeably on a slow machine.  The local mode may be
;; useful in non-editing buffers such as Gnus or PCL-CVS though.

;; An overlay is used.  In the non-sticky cases, this overlay is
;; active only on the selected window.  A hook is added to
;; `post-command-hook' to activate the overlay and move it to the line
;; about point.  To get the non-sticky behavior, `hl-line-unhighlight'
;; is added to `pre-command-hook' as well.  This function deactivates
;; the overlay unconditionally in case the command changes the
;; selected window.  (It does so rather than keeping track of changes
;; in the selected window).

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;; You could make variable `global-hl-line-mode' buffer-local and set
;; it to nil to avoid highlighting specific buffers, when the global
;; mode is used.

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;; By default the whole line is highlighted.  The range of highlighting
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;; can be changed by defining an appropriate function as the
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;; buffer-local value of `hl-line-range-function'.

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;;; Code:

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(defvar-local hl-line-overlay nil
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  "Overlay used by Hl-Line mode to highlight the current line.")

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(defvar-local global-hl-line-overlay nil
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  "Overlay used by Global-Hl-Line mode to highlight the current line.")

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(defvar global-hl-line-overlays nil
  "Overlays used by Global-Hl-Line mode in various buffers.
Global-Hl-Line keeps displaying one overlay in each buffer
when `global-hl-line-sticky-flag' is non-nil.")

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(defgroup hl-line nil
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  "Highlight the current line."
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  :version "21.1"
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  :group 'convenience)
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(defface hl-line
  '((t :inherit highlight))
  "Default face for highlighting the current line in Hl-Line mode."
  :version "22.1"
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  :group 'hl-line)

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(defcustom hl-line-face 'hl-line
  "Face with which to highlight the current line in Hl-Line mode."
  :type 'face
  :group 'hl-line
  :set (lambda (symbol value)
	 (set symbol value)
	 (dolist (buffer (buffer-list))
	   (with-current-buffer buffer
	     (when hl-line-overlay
	       (overlay-put hl-line-overlay 'face hl-line-face))))
	 (when global-hl-line-overlay
	   (overlay-put global-hl-line-overlay 'face hl-line-face))))

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(defcustom hl-line-sticky-flag t
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  "Non-nil means the HL-Line mode highlight appears in all windows.
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Otherwise Hl-Line mode will highlight only in the selected
window.  Setting this variable takes effect the next time you use
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the command `hl-line-mode' to turn Hl-Line mode on.

This variable has no effect in Global Highlight Line mode.
For that, use `global-hl-line-sticky-flag'."
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  :type 'boolean
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  :version "22.1"
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  :group 'hl-line)

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(defcustom global-hl-line-sticky-flag nil
  "Non-nil means the Global HL-Line mode highlight appears in all windows.
Otherwise Global Hl-Line mode will highlight only in the selected
window.  Setting this variable takes effect the next time you use
the command `global-hl-line-mode' to turn Global Hl-Line mode on."
  :type 'boolean
  :version "24.1"
  :group 'hl-line)

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(defvar hl-line-range-function nil
  "If non-nil, function to call to return highlight range.
The function of no args should return a cons cell; its car value
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is the beginning position of highlight and its cdr value is the
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end position of highlight in the buffer.
It should return nil if there's no region to be highlighted.

This variable is expected to be made buffer-local by modes.")

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(defvar hl-line-overlay-buffer nil
  "Most recently visited buffer in which Hl-Line mode is enabled.")

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;;;###autoload
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(define-minor-mode hl-line-mode
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  "Toggle highlighting of the current line (Hl-Line mode).
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Hl-Line mode is a buffer-local minor mode.  If
`hl-line-sticky-flag' is non-nil, Hl-Line mode highlights the
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line about the buffer's point in all windows.  Caveat: the
buffer's point might be different from the point of a
non-selected window.  Hl-Line mode uses the function
`hl-line-highlight' on `post-command-hook' in this case.

When `hl-line-sticky-flag' is nil, Hl-Line mode highlights the
line about point in the selected window only.  In this case, it
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uses the function `hl-line-maybe-unhighlight' in
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addition to `hl-line-highlight' on `post-command-hook'."
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  :group 'hl-line
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  (if hl-line-mode
      (progn
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        ;; In case `kill-all-local-variables' is called.
        (add-hook 'change-major-mode-hook #'hl-line-unhighlight nil t)
        (hl-line-highlight)
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        (setq hl-line-overlay-buffer (current-buffer))
	(add-hook 'post-command-hook #'hl-line-highlight nil t)
        (add-hook 'post-command-hook #'hl-line-maybe-unhighlight nil t))
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    (remove-hook 'post-command-hook #'hl-line-highlight t)
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    (hl-line-unhighlight)
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    (remove-hook 'change-major-mode-hook #'hl-line-unhighlight t)
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    (remove-hook 'post-command-hook #'hl-line-maybe-unhighlight t)))
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(defun hl-line-make-overlay ()
  (let ((ol (make-overlay (point) (point))))
    (overlay-put ol 'priority -50)           ;(bug#16192)
    (overlay-put ol 'face hl-line-face)
    ol))

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(defun hl-line-highlight ()
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  "Activate the Hl-Line overlay on the current line."
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  (if hl-line-mode	; Might be changed outside the mode function.
      (progn
        (unless hl-line-overlay
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          (setq hl-line-overlay (hl-line-make-overlay))) ; To be moved.
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        (overlay-put hl-line-overlay
                     'window (unless hl-line-sticky-flag (selected-window)))
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	(hl-line-move hl-line-overlay))
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    (hl-line-unhighlight)))
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(defun hl-line-unhighlight ()
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  "Deactivate the Hl-Line overlay on the current line."
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  (when hl-line-overlay
    (delete-overlay hl-line-overlay)))
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(defun hl-line-maybe-unhighlight ()
  "Maybe deactivate the Hl-Line overlay on the current line.
Specifically, when `hl-line-sticky-flag' is nil deactivate all
such overlays in all buffers except the current one."
  (let ((hlob hl-line-overlay-buffer)
        (curbuf (current-buffer)))
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    (when (and (buffer-live-p hlob)
               (not hl-line-sticky-flag)
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               (not (eq curbuf hlob))
               (not (minibufferp)))
      (with-current-buffer hlob
        (when (overlayp hl-line-overlay)
          (delete-overlay hl-line-overlay))))
    (when (and (overlayp hl-line-overlay)
               (eq (overlay-buffer hl-line-overlay) curbuf))
      (setq hl-line-overlay-buffer curbuf))))

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;;;###autoload
(define-minor-mode global-hl-line-mode
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  "Toggle line highlighting in all buffers (Global Hl-Line mode).
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If `global-hl-line-sticky-flag' is non-nil, Global Hl-Line mode
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highlights the line about the current buffer's point in all live
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windows.

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Global-Hl-Line mode uses the functions `global-hl-line-highlight'
and `global-hl-line-maybe-unhighlight' on `post-command-hook'."
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  :global t
  :group 'hl-line
  (if global-hl-line-mode
      (progn
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        ;; In case `kill-all-local-variables' is called.
        (add-hook 'change-major-mode-hook #'global-hl-line-unhighlight)
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        (global-hl-line-highlight-all)
	(add-hook 'post-command-hook #'global-hl-line-highlight)
        (add-hook 'post-command-hook #'global-hl-line-maybe-unhighlight))
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    (global-hl-line-unhighlight-all)
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    (remove-hook 'post-command-hook #'global-hl-line-highlight)
    (remove-hook 'change-major-mode-hook #'global-hl-line-unhighlight)
    (remove-hook 'post-command-hook #'global-hl-line-maybe-unhighlight)))
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(defun global-hl-line-highlight ()
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  "Highlight the current line in the current window."
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  (when global-hl-line-mode	; Might be changed outside the mode function.
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    (unless (window-minibuffer-p)
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      (unless global-hl-line-overlay
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        (setq global-hl-line-overlay (hl-line-make-overlay))) ; To be moved.
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      (unless (member global-hl-line-overlay global-hl-line-overlays)
	(push global-hl-line-overlay global-hl-line-overlays))
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      (overlay-put global-hl-line-overlay 'window
		   (unless global-hl-line-sticky-flag
		     (selected-window)))
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      (hl-line-move global-hl-line-overlay))))
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(defun global-hl-line-highlight-all ()
  "Highlight the current line in all live windows."
  (walk-windows (lambda (w)
                  (with-current-buffer (window-buffer w)
                    (global-hl-line-highlight)))
                nil t))

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(defun global-hl-line-unhighlight ()
  "Deactivate the Global-Hl-Line overlay on the current line."
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  (when global-hl-line-overlay
    (delete-overlay global-hl-line-overlay)))
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(defun global-hl-line-maybe-unhighlight ()
  "Maybe deactivate the Global-Hl-Line overlay on the current line.
Specifically, when `global-hl-line-sticky-flag' is nil deactivate
all such overlays in all buffers except the current one."
  (mapc (lambda (ov)
	  (let ((ovb (overlay-buffer ov)))
            (when (and (not global-hl-line-sticky-flag)
                       (bufferp ovb)
                       (not (eq ovb (current-buffer)))
                       (not (minibufferp)))
		(with-current-buffer ovb
                  (when (overlayp global-hl-line-overlay)
                    (delete-overlay global-hl-line-overlay))))))
        global-hl-line-overlays))

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(defun global-hl-line-unhighlight-all ()
  "Deactivate all Global-Hl-Line overlays."
  (mapc (lambda (ov)
	  (let ((ovb (overlay-buffer ov)))
	    (when (bufferp ovb)
		(with-current-buffer ovb
		  (global-hl-line-unhighlight)))))
	global-hl-line-overlays)
  (setq global-hl-line-overlays nil))

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(defun hl-line-move (overlay)
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  "Move the Hl-Line overlay.
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If `hl-line-range-function' is non-nil, move the OVERLAY to the position
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where the function returns.  If `hl-line-range-function' is nil, fill
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the line including the point by OVERLAY."
  (let (tmp b e)
    (if hl-line-range-function
	(setq tmp (funcall hl-line-range-function)
	      b   (car tmp)
	      e   (cdr tmp))
      (setq tmp t
	    b (line-beginning-position)
	    e (line-beginning-position 2)))
    (if tmp
	(move-overlay overlay b e)
      (move-overlay overlay 1 1))))

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(defun hl-line-unload-function ()
  "Unload the Hl-Line library."
  (global-hl-line-mode -1)
  (save-current-buffer
    (dolist (buffer (buffer-list))
      (set-buffer buffer)
      (when hl-line-mode (hl-line-mode -1))))
  ;; continue standard unloading
  nil)

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(provide 'hl-line)

;;; hl-line.el ends here