highlight-indent-guides.el

This minor mode highlights indentation levels via font-lock. Indent widths are dynamically discovered, which means this correctly highlights in any mode, regardless of indent width, even in languages with non-uniform indentation such as Haskell. By default, this mode also inspects your theme dynamically, and automatically chooses appropriate colors for highlighting. This mode works properly around hard tabs and mixed indentation, and it behaves well in large buffers.

Screenshots

M-x customize-variable RET highlight-indent-guides-method RET ...

'fill	'column

'character	'bitmap

Installation

To install from Melpa, use M-x package-install RET highlight-indent-guides RET.

To install from GNU Guix, run guix install emacs-highlight-indent-guides.

Otherwise, download highlight-indent-guides.el and put it in your load path.

Usage

Once the mode is installed, do M-x highlight-indent-guides-mode to enable it. To enable it automatically in most programming modes, use the following:

(add-hook 'prog-mode-hook 'highlight-indent-guides-mode)

Configuration

This mode supports four display methods. To change the display method, customize highlight-indent-guides-method, and set it to one of the following:

• fill: The default method. All whitespace used for indentation is highlighted. The color of each level of indentation alternates between highlight-indent-guides-odd-face and highlight-indent-guides-even-face.
• column: Like fill, but only the first column of each level of indentation is highlighted.
• character: The first column of each level of indentation is drawn using a column of characters. The character to draw with is specified by highlight-indent-guides-character, and it is drawn using the face highlight-indent-guides-character-face.
• bitmap: Like character, but an image is used in place of a character. This provides a wider variety of appearance options, and ensures that guides are always flush, not broken if the line height exceeds the character height. The image to use can be set by overloading the highlight-indent-guides-bitmap-function variable with a custom function.

For example:

M-x customize-variable RET highlight-indent-guides-method RET 'character

To change the character used for drawing guide lines with the character display method, customize highlight-indent-guides-character.

For example:

M-x customize-variable RET highlight-indent-guides-character RET ?|

Highlight Colors

By default, this mode dynamically chooses colors that look acceptable with the loaded theme. It does this by altering the luminosity of the theme's background color by a given percentage. These percentages can be tweaked, to make the colors more intense or subtle.

For example:

M-x customize-variable RET highlight-indent-guides-auto-odd-face-perc RET 15 M-x customize-variable RET highlight-indent-guides-auto-even-face-perc RET 15 M-x customize-variable RET highlight-indent-guides-auto-character-face-perc RET 20

To set the colors manually, disable this feature and customize the faces directly.

For example:

M-x customize-variable RET highlight-indent-guides-auto-enabled RET nil

(set-face-background 'highlight-indent-guides-odd-face "darkgray")
(set-face-background 'highlight-indent-guides-even-face "dimgray")
(set-face-foreground 'highlight-indent-guides-character-face "dimgray")

In some configurations, the following error might show up when emacs starts:

Error: highlight-indent-guides cannot auto set faces: `default' face is not set properly

This is meant as a warning for when the faces can't be set, but in some situations the error might show up even when the faces are set properly. If this happens regularly, the error can be suppressed by customizing highlight-indent-guides-suppress-auto-error:

M-x customize-variable RET highlight-indent-guides-suppress-auto-error RET t

Responsive Guides

Responsive guides allow you to visualize not only the indentation itself, but your place in it. To enable this feature, customize highlight-indent-guides-responsive, and set it to one of the following:

• nil: The default. Responsive guides are disabled.
• top: Use a different color to highlight the "current" guide (the indentation block of the line that the cursor is on). This changes as the cursor moves.
• stack: Like top, but also use a third color for all "ancestor" guides of the current guide. Again, this will change as the cursor moves around.

By default, responsive guides are not updated immediately every time the cursor moves. Instead, guides only update after the cursor stops moving for a certain period of time (one tenth of a second, by default). If you would like to change this behavior, customize highlight-indent-guides-delay, and set it to the number of seconds to wait. For example, to disable the delay entirely:

M-x customize-variable RET highlight-indent-guides-delay RET 0

Enabling this feature provides more highlight faces, as well as more color modifiers for the dynamic colors feature. These are specified in the following table:

Custom Highlighter Function

The highlighter function is the function that calculates which faces to use to display each guide character. If the default highlighter function isn't doing it for you, you can write your own by customizing highlight-indent-guides-highlighter-function. A custom highlighter takes three parameters:

• level: The indent level this guide character exists at, starting at 0.
• responsive: The responsive class of this guide character. This can be nil, top, or stack.
• display: The display method setting. One of fill, column, character, or bitmap.

A custom highlighter should return the face to use to color the given guide character. Alternatively, it may return nil to specify that the guide should not be displayed at all.

The highlighter function is called once for each indentation character, each time a section of the buffer is re-highlighted. To speed things up a little, the results of the highlighter function are memoized per-character, and are reused when possible. Because of this, a custom highlighter should run quickly, and should not have side-effects (i.e. it should not depend on or change external values that might differ from one call to the next). A custom highlighter can return custom faces, but those faces will not be recognized by the dynamic color feature, and will need to be defined and colored manually.

The following example highlighter will highlight normally, except that it will not highlight the first two levels of indentation:

(defun my-highlighter (level responsive display)
  (if (> 2 level)
      nil
    (highlight-indent-guides--highlighter-default level responsive display)))

(setq highlight-indent-guides-highlighter-function 'my-highlighter)

Custom Bitmap Function

If you're using the 'bitmap display method, you may set a custom bitmap function, which determines what your guides will look like. Customize highlight-indent-guides-bitmap-function, and set it to:

• highlight-indent-guides--bitmap-dots: A guide is a column of small dots. This is the default.
• highlight-indent-guides--bitmap-line: A guide is a solid vertical line.
• Or, write your own.

A custom bitmap function takes four parameters:

• width: The width in pixels of the bitmap.
• height: The height in pixels of the bitmap.
• crep: A character that represents a "filled" or "colored" pixel. This is as opposed to an "empty" pixel, which the background color will show through.
• zrep: A character that represents an "empty" pixel.

The function should return a list of string lists, representing the pixels themselves. The list must contain height sublists, and each sublist must contain width strings, all of which are either crep for a colored pixel or zrep for an empty pixel.

Limitations

To display the character method guides, and to highlight tab characters correctly, this mode controls the display text property of some characters via font-lock. Therefore, this mode may or may not play well with other modes that use the display text property. This mode may also interfere with modes that use a display table to modify how whitespace is drawn, e.g., the whitespace minor mode.

The bitmap display method can only be used if emacs is compiled with xpm support, and is running in gui mode.

Currently, with the way this mode is designed, there is no good way to display indent guides on empty lines.

Alternatives