Highlight diffs

The diff language colours added, removed and context lines, and highlights the code inside each hunk as whatever language the diff header names. Nothing has to be configured: the +++ path decides, and Lumis loads that language during the same pass.

JavaScript
Rust
Elixir
CLI

import diff from '@lumis-sh/lumis/langs/diff'
import elixir from '@lumis-sh/lumis/langs/elixir'

const hl = await createHighlighter({languages: [diff, elixir]})
const output = hl.highlight(source, htmlInline({language: diff, theme: frappe}))

let html = highlight(source, HtmlInlineBuilder::new()
    .language(Language::Diff)
    .theme(Some(themes::get("catppuccin_frappe").unwrap()))
    .build()
    .unwrap());

Lumis.highlight!(source, formatter: {:html_inline, language: "diff", theme: "catppuccin_frappe"})

git diff | lumis highlight -l diff

Given this input:

diff --git a/lib/varsel.ex b/lib/varsel.ex
--- a/lib/varsel.ex
+++ b/lib/varsel.ex
@@ -1,6 +1,6 @@
 defmodule Varsel do
   def run(json) do
-    File.write!(path, Jason.encode!(json))
+    File.write!(path, JSON.encode!(json))
   end
 end

defmodule, def and end are Elixir keywords, File and JSON are modules, and the changed lines keep their diff.plus and diff.minus colours around that.

A git diff of an Elixir file, rendered with catppuccin_frappe: the unchanged lines
carry Elixir keyword, module and atom colours, and the removed and added lines
keep their red and green backgrounds underneath them.

Which language a hunk gets

From the +++ path, matched against the same file name globs that lumis languages list reports, so +++ b/lib/varsel.ex selects Elixir. A path Lumis has no language for, including /dev/null, leaves the hunk uncoloured but still marks its added and removed lines.

In the browser, load the inner language up front along with diff. web-tree-sitter cannot fetch a parser inside a synchronous walk, so a language first named by a diff header has to already be there. Node, the CLI, Elixir and Rust load it on demand.

Which language a hunk gets​

Which language a hunk gets