pkgs-lib: allow paths in TOML, YAML and JSON

Paths get automatically added to the store. The INI generator currently chokes
on paths, so it is not supported for now.

pkgs/pkgs-lib/formats.nix

@@ -30,6 +30,7 @@ rec {
         int
         float
         str
+        path
         (attrsOf valueType)
         (listOf valueType)
       ]) // {
@@ -112,6 +113,7 @@ rec {
         int
         float
         str
+        path
         (attrsOf valueType)
         (listOf valueType)
       ] // {

pkgs/pkgs-lib/tests/formats.nix

@@ -38,6 +38,7 @@ in runBuildTests {
       str = "foo";
       attrs.foo = null;
       list = [ null null ];
+      path = ./formats.nix;
     };
     expected = ''
       {
@@ -52,6 +53,7 @@ in runBuildTests {
           null
         ],
         "null": null,
+        "path": "${./formats.nix}",
         "str": "foo",
         "true": true
       }
@@ -67,6 +69,7 @@ in runBuildTests {
       str = "foo";
       attrs.foo = null;
       list = [ null null ];
+      path = ./formats.nix;
     };
     expected = ''
       {
@@ -80,6 +83,7 @@ in runBuildTests {
           null
         ],
         "null": null,
+        "path": "${./formats.nix}",
         "str": "foo",
         "true": true
       }