lua-language-server: add smoke test

This was mostly taken from vtsls.

pkgs/by-name/lu/lua-language-server/package.nix

@@ -15,6 +15,8 @@
 
   versionCheckHook,
   nix-update-script,
+  runCommand,
+  lua-language-server,
 }:
 
 stdenv.mkDerivation (finalAttrs: {
@@ -128,7 +130,26 @@ stdenv.mkDerivation (finalAttrs: {
   ];
   doInstallCheck = true;
 
-  passthru.updateScript = nix-update-script { };
+  passthru = {
+    updateScript = nix-update-script { };
+
+    tests.smoke = runCommand "lua-language-server-smoke-test" { } ''
+      export XDG_CACHE_HOME=$(mktemp -d)
+
+      INIT_REQUEST='{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"processId":null,"rootUri":"file:///tmp","workspaceFolders":[{"uri":"file:///tmp","name":"test"}],"capabilities":{}}}'
+      CONTENT_LENGTH=''${#INIT_REQUEST}
+
+      RESPONSE=$(
+        {
+          printf "Content-Length: %d\r\n\r\n%s" "$CONTENT_LENGTH" "$INIT_REQUEST"
+          sleep 1
+        } | timeout 3  ${lib.getExe lua-language-server} --stdio 2>&1 | head -c 1000
+      ) || true
+
+      echo "$RESPONSE" | grep -q '"capabilities"'
+      touch $out
+    '';
+  };
 
   meta = {
     description = "Language server that offers Lua language support";