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.

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.

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

• src/config/mod.rs — the two Options fields.
• src/ui/window_render.rs — build_whitespace_overlay produces a per-cell style map; the line renderer applies it after selection but before :highlight / syntax.