Warn Struct#initialize with only keyword args (#4070)

* Warn Struct#initialize with only keyword args

A part of [Feature #16806]

* Do not warn if `keyword_init: false`

is explicitly specified

* Add a NEWS entry

* s/in/from/

* Make sure all fields are initialized

1 files changed, 12 insertions, 0 deletions

diff --git a/test/ruby/test_struct.rb b/test/ruby/test_struct.rb
index c313ab0dbe..dc6a0b99fd 100644
--- a/test/ruby/test_struct.rb
+++ b/test/ruby/test_struct.rb
@@ -350,6 +350,18 @@ module TestStruct
     end
   end
 
+  def test_keyword_args_warning
+    warning = /warning: Passing only keyword arguments to Struct#initialize will behave differently from Ruby 3\.2\./
+    assert_match(warning, EnvUtil.verbose_warning { assert_equal({a: 1}, @Struct.new(:a).new(a: 1).a) })
+    assert_match(warning, EnvUtil.verbose_warning { assert_equal({a: 1}, @Struct.new(:a, keyword_init: nil).new(a: 1).a) })
+    assert_warn('') { assert_equal({a: 1}, @Struct.new(:a).new({a: 1}).a) }
+    assert_warn('') { assert_equal({a: 1}, @Struct.new(:a, :b).new(1, a: 1).b) }
+    assert_warn('') { assert_equal(1, @Struct.new(:a, keyword_init: true).new(a: 1).a) }
+    assert_warn('') { assert_equal({a: 1}, @Struct.new(:a, keyword_init: nil).new({a: 1}).a) }
+    assert_warn('') { assert_equal({a: 1}, @Struct.new(:a, keyword_init: false).new(a: 1).a) }
+    assert_warn('') { assert_equal({a: 1}, @Struct.new(:a, keyword_init: false).new({a: 1}).a) }
+  end
+
   def test_nonascii
     struct_test = @Struct.new(name = "R\u{e9}sum\u{e9}", :"r\u{e9}sum\u{e9}")
     assert_equal(@Struct.const_get("R\u{e9}sum\u{e9}"), struct_test, '[ruby-core:24849]')