gn: add update script

Signed-off-by: Marcin Serwin <marcin@serwin.dev>

pkgs/by-name/gn/gn/package.nix

@@ -77,6 +77,8 @@ stdenv.mkDerivation {
 
   setupHook = ./setup-hook.sh;
 
+  passthru.updateScript = ./update.sh;
+
   meta = {
     description = "Meta-build system that generates build files for Ninja";
     mainProgram = "gn";

pkgs/by-name/gn/gn/update.sh

@@ -0,0 +1,21 @@
+#!/usr/bin/env nix-shell
+#!nix-shell -i bash -p jq curl common-updater-scripts
+
+set -ex
+
+rev=$(
+  curl --location "https://raw.githubusercontent.com/NixOS/nixpkgs/refs/heads/master/pkgs/applications/networking/browsers/chromium/info.json" \
+  | jq -r ".chromium.deps.gn.rev"
+)
+
+commit_time=$(
+  curl "https://gn.googlesource.com/gn/+/$rev?format=json" \
+  | sed "s/)]}'//" \
+  | jq -r ".committer.time" \
+  | awk '{print $2, $3, $5, $4 $6}'
+)
+
+commit_date=$(TZ= date --date "$commit_time" --iso-8601)
+version="0-unstable-$commit_date"
+
+update-source-version --rev="$rev" --version-key="version" "gn" "$version"