tests: perform code formatting test in test suite

This should improve visibility when CI job fails due to bad
formatting.

2 files changed, 28 insertions, 0 deletions

diff --git a/tests/meta/default.nix b/tests/meta/default.nix
new file mode 100644
index 00000000000..0f02fcfb453
--- /dev/null
+++ b/tests/meta/default.nix
@@ -0,0 +1 @@
+{ meta-formatting = ./formatting.nix; }
diff --git a/tests/meta/formatting.nix b/tests/meta/formatting.nix
new file mode 100644
index 00000000000..2d5800c53cd
--- /dev/null
+++ b/tests/meta/formatting.nix
@@ -0,0 +1,27 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+
+  pinnedNixpkgs = builtins.fetchTarball {
+    url =
+      "https://github.com/NixOS/nixpkgs/archive/05f0934825c2a0750d4888c4735f9420c906b388.tar.gz";
+    sha256 = "1g8c2w0661qn89ajp44znmwfmghbbiygvdzq0rzlvlpdiz28v6gy";
+  };
+
+  pinnedPkgs = import pinnedNixpkgs { };
+
+in {
+  config = {
+    nmt.script = ''
+      PATH="${with pinnedPkgs; lib.makeBinPath [ findutils nixfmt ]}:$PATH"
+      cd ${../..}
+      if ! ${pkgs.runtimeShell} format -c; then
+        fail "${''
+        Expected source code to be formatted with nixfmt but it was not.
+        This error can be resolved by running the './format' in the project root directory.''}"
+      fi
+    '';
+  };
+}