clangd-inactive-regions.el

About

Eglot extension to support the new clangd inactiveRegions LSP capability introduced in clangd-17.

Highlights inactive code in a LSP aware way, taking into account compile time includes and defines for current project.

Listens to inactiveRegions notifications and shades them with one of the available-methods:

• darken-foreground makes inactive code semitransparent blending current foreground and background colors
• shade-background makes inactive code background slightly darker or lighter depending on current theme
• shadow applies the shadow face to inactive code

Screenshots

darken-foreground method, gruvbox dark theme, 30% opacity

Inactive regions are provided by the language server so they will honor your include paths and compile time defines. Here I'm looking at my emacs-29 branch configured to build on MacOS and you can see Windows code is correctly disabled.

shade-background method, modus operandi theme, 10% shading

Installation

(unless (package-installed-p 'clangd-inactive-regions)
  (package-vc-install "https://github.com/fargiolas/clangd-inactive-regions.el"))

You will need at least emacs 29.1 and clangd-17.

Usage

(use-package clangd-inactive-regions
  :init
  (add-hook 'eglot-managed-mode-hook #'clangd-inactive-regions-mode)
  :config
  (clangd-inactive-regions-set-method "darken-foreground")
  (clangd-inactive-regions-set-opacity 0.55))

Caveats

As far as I know Emacs doesn't have a way to set foreground text opacity. Best would be a face attribute so that you can set it in an overlay covering each inactive region and be done with it. Unfortunately there is no attribute for this yet.

Hence darken-foreground method is a fragile and inefficient hack around fontification: for each inactive region it looks for symbols with different faces and applies to each of them a different overlay with a dimmed foreground color.

It seems to work with cc and c-ts modes and I've been using it daily for more than a year now, but could totally break other modes or features I'm not aware of.

If you know a better way please do let me know.