lib/types: change pathInStore to allow leading period

As of [nix v2.21.0](https://nix.dev/manual/nix/2.25/release-notes/rl-2.21.html):

> Store paths are allowed to start with `.`

I'm not entirely sure what range of versions of `nix` we try to stay
compatible with over here in `nixpkgs`. That said, I don't think
particular change would cause issues for people using a version of `nix`
that doesn't support leading periods.

lib/tests/modules.sh

@@ -164,11 +164,11 @@ checkConfigError 'In attrTag, each tag value must be an option, but tag int was
 checkConfigOutput '".*/store/0lz9p8xhf89kb1c1kk6jxrzskaiygnlh-bash-5.2-p15.drv"' config.pathInStore.ok1 ./types.nix
 checkConfigOutput '".*/store/0fb3ykw9r5hpayd05sr0cizwadzq1d8q-bash-5.2-p15"' config.pathInStore.ok2 ./types.nix
 checkConfigOutput '".*/store/0fb3ykw9r5hpayd05sr0cizwadzq1d8q-bash-5.2-p15/bin/bash"' config.pathInStore.ok3 ./types.nix
+checkConfigOutput '".*/store/\.links"' config.pathInStore.ok4 ./types.nix
 checkConfigError 'A definition for option .* is not of type .path in the Nix store.. Definition values:\n\s*- In .*: ""' config.pathInStore.bad1 ./types.nix
 checkConfigError 'A definition for option .* is not of type .path in the Nix store.. Definition values:\n\s*- In .*: ".*/store"' config.pathInStore.bad2 ./types.nix
 checkConfigError 'A definition for option .* is not of type .path in the Nix store.. Definition values:\n\s*- In .*: ".*/store/"' config.pathInStore.bad3 ./types.nix
-checkConfigError 'A definition for option .* is not of type .path in the Nix store.. Definition values:\n\s*- In .*: ".*/store/.links"' config.pathInStore.bad4 ./types.nix
-checkConfigError 'A definition for option .* is not of type .path in the Nix store.. Definition values:\n\s*- In .*: "/foo/bar"' config.pathInStore.bad5 ./types.nix
+checkConfigError 'A definition for option .* is not of type .path in the Nix store.. Definition values:\n\s*- In .*: "/foo/bar"' config.pathInStore.bad4 ./types.nix
 
 # Check boolean option.
 checkConfigOutput '^false$' config.enable ./declare-enable.nix

lib/tests/modules/types.nix

@@ -15,10 +15,10 @@ in
     pathInStore.ok1 = "${storeDir}/0lz9p8xhf89kb1c1kk6jxrzskaiygnlh-bash-5.2-p15.drv";
     pathInStore.ok2 = "${storeDir}/0fb3ykw9r5hpayd05sr0cizwadzq1d8q-bash-5.2-p15";
     pathInStore.ok3 = "${storeDir}/0fb3ykw9r5hpayd05sr0cizwadzq1d8q-bash-5.2-p15/bin/bash";
+    pathInStore.ok4 = "${storeDir}/.links";
     pathInStore.bad1 = "";
     pathInStore.bad2 = "${storeDir}";
     pathInStore.bad3 = "${storeDir}/";
-    pathInStore.bad4 = "${storeDir}/.links"; # technically true, but not reasonable
-    pathInStore.bad5 = "/foo/bar";
+    pathInStore.bad4 = "/foo/bar";
   };
 }

lib/types.nix

@@ -577,7 +577,7 @@ rec {
       name = "pathInStore";
       description = "path in the Nix store";
       descriptionClass = "noun";
-      check = x: isStringLike x && builtins.match "${builtins.storeDir}/[^.].*" (toString x) != null;
+      check = x: isStringLike x && builtins.match "${builtins.storeDir}/.+" (toString x) != null;
       merge = mergeEqualOption;
     };