Add tests for path interpolations

Author: Lucus16

.reuse/dep5

@@ -5,6 +5,21 @@ Copyright: 2019 Serokell <hi@serokell.io>
 Copyright: 2019 Lars Jellema <lars.jellema@gmail.com>
 License: MPL-2.0
 
+Files: test/correct/*
+Copyright: 2022 Serokell <hi@serokell.io>
+Copyright: 2022 Lars Jellema <lars.jellema@gmail.com>
+License: MPL-2.0
+
+Files: test/changed/*
+Copyright: 2022 Serokell <hi@serokell.io>
+Copyright: 2022 Lars Jellema <lars.jellema@gmail.com>
+License: MPL-2.0
+
+Files: test/invalid/*
+Copyright: 2022 Serokell <hi@serokell.io>
+Copyright: 2022 Lars Jellema <lars.jellema@gmail.com>
+License: MPL-2.0
+
 Files: flake.lock
 Copyright: 2020 Serokell <hi@serokell.io>
 Copyright: 2022 Yorick van Pelt <yorickvanpelt@gmail.com>

test/README.md

@@ -0,0 +1,14 @@
+<!-- © 2022 Serokell <hi@serokell.io>
+   - © 2022 Lars Jellema <lars.jellema@gmail.com>
+   -
+   - SPDX-License-Identifier: MPL-2.0
+   -->
+
+Tests in `correct` are formatted the way they should be.
+Running `nixfmt --verify` on them should result in the output being the same as
+the input.
+
+Tests in `invalid` should return an error when formatted.
+
+Tests in `changed` have input and output files. `nixfmt --verify foo.in.nix`
+should output exactly `foo.out.nix`.

test/correct/paths-with-interpolations.nix

@@ -0,0 +1,13 @@
+let
+  foo = "foo";
+  bar = "bar";
+
+in [
+  /${foo}
+  ./${foo}
+  /foo/${bar}
+  /foo${bar}
+  /${foo}/bar
+  /${foo}bar
+  /foo${bar}baz
+]

test/invalid/interpolation-in-env-path.nix

@@ -0,0 +1 @@
+<nixpkgs/${"pkgs"}>

test/invalid/naked-interpolation.nix

@@ -0,0 +1 @@
+${"foo"}

test/invalid/path-starting-with-interpolation.nix

@@ -0,0 +1 @@
+${"/foo"}/bar

test/invalid/path-with-escaped-interpolation.nix

@@ -0,0 +1 @@
+/foo\${"bar"}

test/invalid/path-with-interpolation-before-slash.nix

@@ -0,0 +1 @@
+foo${"bar"}/baz