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

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

At the moment the package is little more than an experiment. If you want to try it just copy the .el file somewhere in the load path.

Feedback, issues and pull requests more than welcome!

Usage

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

(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 whole 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 (albeit a little slower than I'd like) but could totally break other modes or features I'm not aware of.

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