rtdvi

Whitespace marks

Two opt-in flags that paint problematic whitespace red, so you spot it before it gets committed.

Configuration

[options]
highlight_trailing_whitespace = true
highlight_tabs                = true

Both default to false. They're independent — set just the one you want.

highlight_trailing_whitespace

Paints every space or tab in the run of whitespace after the last non-whitespace character of a line. A \r immediately before \n (CR-LF stragglers) is also considered trailing whitespace.

Lines that are only whitespace are entirely red.

foo···        ← three trailing spaces, all red
foo bar       ← no trailing whitespace, no red
······        ← whole line is red

highlight_tabs

Paints every tab cell red, wherever the tab appears on the line. Each tab expands to options.tab_width cells (defaulting to 4) and all of them are painted.

→→→→foo       ← red tab expansion
··→→bar       ← spaces stay normal; tab at col 2-3 red
foo→bar       ← tab in the middle, still red

Useful in spaces-only projects where stray tabs are bugs.

nbsp_marker

A non-breaking space (U+00A0) renders identically to a normal space, so it's easy to introduce one by accident (a stray AltGr+space, copy-paste from a word processor) and then wonder why a command, alignment, or shell line behaves oddly. Set nbsp_marker to a glyph and every NBSP is shown as that glyph in a distinct colour instead of a blank:

[options]
nbsp_marker = "·"   # or "°", "+", "␣", …

The first character of the string is used. Empty (the default) leaves NBSP as a blank. So hello·world·42! immediately distinguishes NBSP-separated text from the normal-space hello world 42!.

Can also be toggled at runtime: :set nbsp=· (and :set nbsp= to clear).

space_marker

Show every normal space (U+0020) as a glyph, in a dim colour — vim's listchars space:. Useful for spotting alignment and trailing/leading spaces:

[options]
space_marker = "·"

a·b·c instead of a b c. Tabs and non-breaking spaces are left to their own markers (highlight_tabs, nbsp_marker), and a trailing space still shows its red background (from highlight_trailing_whitespace) on top of the glyph.

Runtime: :set space=· (and :set space= to clear).

Both at once

Set both flags and a trailing tab (or a line of only tabs) is highlighted by either rule — they don't conflict.

Column ruler

color_column highlights one or more screen columns with a background ruler — vim's colorcolumn — so you can see when a line is running past your textwidth.

[options]
textwidth    = 80
color_column = "80"        # mark column 80
# color_column = "80,100"  # several columns
# color_column = "+1"      # column just past textwidth (i.e. 81 here)

The value is a comma-separated list of 1-based columns. An entry with a leading +/- is taken relative to textwidth, so "+1" marks the first column you shouldn't type into. The default is the empty string, which turns the ruler off.

Unlike the whitespace marks, the ruler is painted across the whole height of each real text line — including the empty cells past the end of a short line — so it reads as a continuous vertical guide. It is not drawn on the ~ rows below the end of the buffer.

It can also be toggled at runtime, vim-style:

:set colorcolumn=80      (aliases: :set cc=80, :set color_column=80)
:set colorcolumn=        clear (also :set nocolorcolumn / :set nocc)

Rendering priority

Whitespace marks sit just below the active selection but above :highlight and syntax highlighting (see highlights.md). That means selected cells render as selected; everything else where a mark fires renders red.

Why not always on?

Some files legitimately use trailing whitespace (Markdown's two-space-then-newline for hard breaks, generated test fixtures, etc.). Opt-in keeps the editor from turning into Christmas lights for users who haven't asked for it.

Implementation