Update the Draft 3 and 4 metaschemas.

For draft 4 this pulls in upstream fixes which were not present locally,
notably fixing `id` to not have `format: uri` in it, because location
independent identifiers are indeed not URIs (they're URI references as
later metaschemas use).

For enum, on draft 3 and 4, this also *re-adds* constraints that enum
items MUST be unique and the array non-empty. In later drafts, this
restriction was loosened (see
json-schema-org/json-schema-spec@cf0ec72)
as well as json-schema-org/json-schema-spec#717 (comment)
but in drafts 3 and 4 it is present.

The draft 4 metaschema contains these assertions, the draft 3 one is
still buggy and does not, so they're just applied locally here.

Ref: json-schema-org/json-schema-spec#310

jsonschema/schemas/draft3.json

@@ -15,7 +15,7 @@
 
 		"properties" : {
 			"type" : "object",
-			"additionalProperties" : {"$ref" : "#", "type" : "object"},
+			"additionalProperties" : {"$ref" : "#"},
 			"default" : {}
 		},
 
@@ -47,7 +47,7 @@
 		},
 
 		"dependencies" : {
-			"type" : ["string", "array", "object"],
+			"type" : "object",
 			"additionalProperties" : {
 				"type" : ["string", "array", {"$ref" : "#"}],
 				"items" : {
@@ -75,11 +75,6 @@
 			"default" : false
 		},
 
-		"maxDecimal": {
-			"minimum": 0,
-			"type": "number"
-		},
-
 		"minItems" : {
 			"type" : "integer",
 			"minimum" : 0,
@@ -112,7 +107,9 @@
 		},
 
 		"enum" : {
-			"type" : "array"
+			"type" : "array",
+			"minItems" : 1,
+			"uniqueItems" : true
 		},
 
 		"default" : {
@@ -153,13 +150,11 @@
 		},
 
 		"id" : {
-			"type" : "string",
-			"format" : "uri"
+			"type" : "string"
 		},
 
 		"$ref" : {
-			"type" : "string",
-			"format" : "uri"
+			"type" : "string"
 		},
 
 		"$schema" : {

jsonschema/schemas/draft4.json

@@ -28,12 +28,10 @@
     "type": "object",
     "properties": {
         "id": {
-            "format": "uri",
             "type": "string"
         },
         "$schema": {
-            "type": "string",
-            "format": "uri"
+            "type": "string"
         },
         "title": {
             "type": "string"
@@ -122,7 +120,9 @@
             }
         },
         "enum": {
-            "type": "array"
+            "type": "array",
+            "minItems": 1,
+            "uniqueItems": true
         },
         "type": {
             "anyOf": [

jsonschema/tests/test_validators.py

@@ -1453,17 +1453,35 @@ def test_enum_allows_empty_arrays(self):
         """
         Technically, all the spec says is they SHOULD have elements, not MUST.
 
+        (As of Draft 6. Previous drafts do say MUST).
+
         See #529.
         """
-        self.Validator.check_schema({"enum": []})
+        if self.Validator in {
+            validators.Draft3Validator,
+            validators.Draft4Validator,
+        }:
+            with self.assertRaises(exceptions.SchemaError):
+                self.Validator.check_schema({"enum": []})
+        else:
+            self.Validator.check_schema({"enum": []})
 
     def test_enum_allows_non_unique_items(self):
         """
         Technically, all the spec says is they SHOULD be unique, not MUST.
 
+        (As of Draft 6. Previous drafts do say MUST).
+
         See #529.
         """
-        self.Validator.check_schema({"enum": [12, 12]})
+        if self.Validator in {
+            validators.Draft3Validator,
+            validators.Draft4Validator,
+        }:
+            with self.assertRaises(exceptions.SchemaError):
+                self.Validator.check_schema({"enum": [12, 12]})
+        else:
+            self.Validator.check_schema({"enum": [12, 12]})
 
 
 class ValidatorTestMixin(MetaSchemaTestsMixin, object):