Make State#configure and #merge only write the options they are given

lib/json/truffle_ruby/generator.rb

@@ -302,10 +302,13 @@ def configure(options)
         end
         alias merge configure
 
+        # Defaults are the current values so that #configure only writes what it was given.
         private def _configure(
-          indent: '', space: '', space_before: '', object_nl: '', array_nl: '', allow_nan: false,
-          as_json: false, ascii_only: false, sort_keys: false, depth: 0, buffer_initial_length: 1024,
-          allow_duplicate_key: false, script_safe: false, strict: false, max_nesting: 100
+          indent: @indent, space: @space, space_before: @space_before, object_nl: @object_nl,
+          array_nl: @array_nl, allow_nan: @allow_nan, as_json: @as_json, ascii_only: @ascii_only,
+          sort_keys: @sort_keys, depth: @depth, buffer_initial_length: @buffer_initial_length,
+          allow_duplicate_key: @allow_duplicate_key, script_safe: @script_safe, strict: @strict,
+          max_nesting: @max_nesting
         )
           if depth.negative?
             raise ArgumentError, "depth must be >= 0 (got #{depth})"

test/json/json_generator_test.rb

@@ -516,6 +516,47 @@ def test_configure_using_configure_and_merge
     assert_equal '5', state2.array_nl
   end
 
+  def test_configure_only_writes_the_string_options_it_is_given
+    state = JSON.state.new(indent: '1', space: '2', space_before: '3', object_nl: '4', array_nl: '5')
+    state.configure(space: '9')
+    assert_equal '1', state.indent
+    assert_equal '9', state.space
+    assert_equal '3', state.space_before
+    assert_equal '4', state.object_nl
+    assert_equal '5', state.array_nl
+    state.merge(array_nl: '8')
+    assert_equal '1', state.indent
+    assert_equal '9', state.space
+    assert_equal '3', state.space_before
+    assert_equal '4', state.object_nl
+    assert_equal '8', state.array_nl
+  end
+
+  def test_configure_keeps_the_layout_of_a_pretty_state
+    state = JSON.state.new(indent: '  ', object_nl: "\n", array_nl: "\n")
+    state.configure(depth: 0)
+    assert_equal %({\n  "foo":[\n    1\n  ]\n}), state.generate({ 'foo' => [1] })
+  end
+
+  def test_configure_only_writes_the_other_options_it_is_given
+    omit 'JRuby resets the non-string options' if RUBY_ENGINE == 'jruby'
+    state = JSON.state.new(max_nesting: 3, allow_nan: true, ascii_only: true, script_safe: true)
+    state.configure(indent: '1')
+    assert_equal '1', state.indent
+    assert_equal 3, state.max_nesting
+    assert_equal true, state.allow_nan?
+    assert_equal true, state.ascii_only?
+    assert_equal true, state.script_safe?
+  end
+
+  def test_configure_writes_a_string_option_given_as_nil
+    omit 'JRuby keeps the previous value for an explicit nil' if RUBY_ENGINE == 'jruby'
+    state = JSON.state.new(indent: '1', space: '2')
+    state.configure(indent: nil)
+    assert_equal '', state.indent
+    assert_equal '2', state.space
+  end
+
   def test_configure_hash_conversion
     state = JSON.state.new
     state.configure(indent: '1')