Return parent base URI when resolving ids

This is necessary because `$id` values are joined with the base URI when
the [instance is validated][0] as well as when [ref JSON pointers are
resolved][1]. This returns the parent base URI instead so that calling
`join_uri` later will generate the correct base URI. There's probably a
better way to do this but I get confused thinking it through.

This came up while working on adding support for draft 2019-09, which
has [tests][2] that caused issues. That's where I pulled these tests
from.

[0]: https://github.com/davishmcclurg/json_schemer/blob/c33c1b91ca831c01270cd7d14f927b8727022dee/lib/json_schemer/schema/base.rb#L137
[1]: https://github.com/davishmcclurg/json_schemer/blob/c33c1b91ca831c01270cd7d14f927b8727022dee/lib/json_schemer/schema/base.rb#L340
[2]: https://github.com/json-schema-org/JSON-Schema-Test-Suite/blob/b069ac352c3dc1fae71f6f177dafe97001c97920/tests/draft2019-09/refRemote.json#L101-L160

lib/json_schemer/schema/base.rb

@@ -330,10 +330,10 @@ def validate_ref(instance, ref, &block)
           child(resolve_ref(ref_uri), base_uri: ref_uri)
         end
 
-        ref_schema, ref_schema_pointer = ref_object.ids[ref_uri] || [ref_object.root, '']
+        ref_schema, ref_schema_pointer, ref_parent_base_uri = ref_object.ids[ref_uri] || [ref_object.root, '', ref_uri]
 
         ref_uri_pointer_parts = Hana::Pointer.parse(URI.decode_www_form_component(ref_uri_pointer))
-        schema, base_uri = ref_uri_pointer_parts.reduce([ref_schema, ref_uri]) do |(obj, uri), token|
+        schema, base_uri = ref_uri_pointer_parts.reduce([ref_schema, ref_parent_base_uri]) do |(obj, uri), token|
           if obj.is_a?(Array)
             [obj.fetch(token.to_i), uri]
           else
@@ -646,16 +646,18 @@ def resolve_ids(schema, ids = {}, base_uri = @base_uri, pointer = '')
         if schema.is_a?(Array)
           schema.each_with_index { |subschema, index| resolve_ids(subschema, ids, base_uri, "#{pointer}/#{index}") }
         elsif schema.is_a?(Hash)
-          uri = join_uri(base_uri, schema[id_keyword])
+          if schema.key?(id_keyword)
+            parent_base_uri = base_uri
+            base_uri = join_uri(base_uri, schema[id_keyword])
+            ids[base_uri] ||= [schema, pointer, parent_base_uri]
+          end
           schema.each do |key, value|
             case key
-            when id_keyword
-              ids[uri] ||= [schema, pointer]
             when 'items', 'allOf', 'anyOf', 'oneOf', 'additionalItems', 'contains', 'additionalProperties', 'propertyNames', 'if', 'then', 'else', 'not'
-              resolve_ids(value, ids, uri, "#{pointer}/#{key}")
+              resolve_ids(value, ids, base_uri, "#{pointer}/#{key}")
             when 'properties', 'patternProperties', 'definitions', 'dependencies'
               value.each do |subkey, subvalue|
-                resolve_ids(subvalue, ids, uri, "#{pointer}/#{key}/#{subkey}")
+                resolve_ids(subvalue, ids, base_uri, "#{pointer}/#{key}/#{subkey}")
               end
             end
           end

test/ref_test.rb

@@ -239,4 +239,66 @@ def test_it_handles_windows_paths
       refute(schema.valid?(1))
     end
   end
+
+  def test_it_handles_base_uri_change_folder
+    schema = JSONSchemer.schema(
+      {
+        '$id' => 'http://localhost:1234/draft2019-09/scope_change_defs1.json',
+        'type' => 'object',
+        'definitions' => {
+          'baz' => {
+            '$id' => 'baseUriChangeFolder/',
+            'type' => 'array',
+            'items' => {
+              '$ref' => 'folderInteger.json'
+            }
+          }
+        },
+        'properties' => {
+          'list' => {
+            '$ref' => 'baseUriChangeFolder/'
+          }
+        }
+      },
+      :ref_resolver => proc do |uri|
+        assert_equal(URI('http://localhost:1234/draft2019-09/baseUriChangeFolder/folderInteger.json'), uri)
+        '{ "type": "integer" }'
+      end
+    )
+    assert(schema.valid?({ 'list' => [1] }))
+    refute(schema.valid?({ 'list' => ['a'] }))
+  end
+
+  def test_it_handles_base_uri_change_folder_in_subschema
+    schema = JSONSchemer.schema(
+      {
+        '$id' => 'http://localhost:1234/draft2019-09/scope_change_defs2.json',
+        'type' => 'object',
+        'definitions' => {
+          'baz' => {
+            '$id' => 'baseUriChangeFolderInSubschema/',
+            'definitions' => {
+              'bar' => {
+                'type' => 'array',
+                'items' => {
+                  '$ref' => 'folderInteger.json'
+                }
+              }
+            }
+          }
+        },
+        'properties' => {
+          'list' => {
+            '$ref' => 'baseUriChangeFolderInSubschema/#/definitions/bar'
+          }
+        }
+      },
+      :ref_resolver => proc do |uri|
+        assert_equal(URI('http://localhost:1234/draft2019-09/baseUriChangeFolderInSubschema/folderInteger.json'), uri)
+        '{ "type": "integer" }'
+      end
+    )
+    assert(schema.valid?({ 'list' => [1] }))
+    refute(schema.valid?({ 'list' => ['a'] }))
+  end
 end