RunOrComp

Elixir compile-time detection via compiler tracing. Produces a JSON database that editor plugins can use to highlight code that runs at compile time vs runtime.

Includes a Neovim plugin that highlights compile-time lines with a subtle background tint and virtual text labels.

How it works

RunOrComp uses Elixir's compilation tracer to observe which code constructs execute at compile time:

• Macro calls from non-stdlib dependencies (e.g., Plug.Builder.plug/1)
• Module-level function calls (e.g., Mix.env/0, Application.compile_env/3)
• Compile-time callbacks — dynamically discovered by scanning dependency source for __before_compile__ macros and the callbacks they invoke (e.g., Plug.Builder calls init/1 at compile time)

Standard library modules, Kernel constructs, and language plumbing are filtered out so only meaningful compile-time indicators remain.

Setup

Add runorcomp to your project's dependencies:

defp deps do
  [
    {:runorcomp, "~> 0.1.0", only: [:dev, :test], runtime: false}
  ]
end

Then configure the tracer and compiler in your project:

def project do
  [
    compilers: Mix.compilers() ++ [:runorcomp],
    elixirc_options: [tracers: [Runorcomp.Tracer]],
    # ...
  ]
end

The tracer runs during mix compile and the compiler writes the database to _build/{env}/runorcomp.json after each compilation pass. Incremental compilation is supported — only recompiled files are re-traced, and existing data for unchanged files is preserved.

Note: .exs files (like mix.exs or test support files) are not traced — only .ex files compiled by mix compile are included.

Neovim plugin

The included Neovim plugin reads the JSON database and highlights compile-time lines with a subtle background tint and optional virtual text labels.

Installation (lazy.nvim)

{
  "dbernheisel/runorcomp",
  ft = "elixir",
  config = function()
    vim.api.nvim_set_hl(0, "RunorcompCompileTime", { bg = "#1a1a2e" })
    vim.api.nvim_set_hl(0, "RunorcompLabel", { fg = "#6e6ea8", italic = true })
    require("runorcomp").setup()
  end,
}

Commands

• :RunorcompRefresh — re-read the database and update highlights
• :RunorcompClear — remove all highlights
• :RunorcompToggleLabels — toggle virtual text labels on/off

Options

require("runorcomp").setup({
  virtual_text = true, -- show "← target" labels (default: true)
})

Highlight groups

Compile-time callbacks (like init/1 called by Plug.Builder) highlight the entire function body, not just the def line.