Data.define single-attribute class rejects positional arguments #9214
Description
Environment Information
- JRuby version:
jruby 10.0.2.0 (3.4.2) 2025-08-07 cba6031bd0 OpenJDK 64-Bit Server VM 21.0.10+7-LTS on 21.0.10+7-LTS +indy +jit [arm64-darwin] - Operating system: macOS (Darwin 25.2.0, arm64-darwin)
- Java version: OpenJDK 21.0.10 (Corretto-21.0.10.7.1)
Expected Behavior
When a method uses both *args and **kwargs parameters and calls another method with both splat operators, the arguments should be properly unpacked and passed through - matching MRI Ruby 3.4.4 behavior.
Actual Behavior
given jruby_bug.rb:
#!/usr/bin/env ruby
puts "Ruby: #{RUBY_DESCRIPTION}\n"
# Test 1: Splat forwarding works fine with regular methods
def regular_method(arg)
arg
end
def test_splat_forwarding(*args, **kwargs)
regular_method(*args, **kwargs)
end
puts "✓ Test 1 - Splat forwarding to regular method: #{test_splat_forwarding("works")}"
# Test 2: Data.define works fine without splat forwarding
MyData = Data.define(:value)
def test_data_no_splat(arg)
MyData.new(arg)
end
puts "✓ Test 2 - Data.define without splat forwarding: #{test_data_no_splat("works").value}"
# Test 3: FAILS - Data.define with BOTH *args and **kwargs
def test_data_with_both_splats(*args, **kwargs)
MyData.new(*args, **kwargs)
end
begin
puts "✓ Test 3 - Data.define with both splats: #{test_data_with_both_splats("fails").value}"
rescue ArgumentError => e
puts "✗ Test 3 - Data.define with both splats: #{e.class}: #{e.message}"
end
# Test 4: Works with only *args (no **kwargs)
def test_data_with_only_args(*args)
MyData.new(*args)
end
puts "✓ Test 4 - Data.define with only *args: #{test_data_with_only_args("works").value}"
with MRI 3.4.4:
Ruby: ruby 3.4.4 (2025-05-14 revision a38531fd3f) +PRISM [arm64-darwin24]
✓ Test 1 - Splat forwarding to regular method: works
✓ Test 2 - Data.define without splat forwarding: works
✓ Test 3 - Data.define with both splats: fails
✓ Test 4 - Data.define with only *args: works
with JRuby 10.0.2.0:
Ruby: jruby 10.0.2.0 (3.4.2) 2025-08-07 cba6031bd0 OpenJDK 64-Bit Server VM 21.0.10+7-LTS on 21.0.10+7-LTS +indy +jit [arm64-darwin]
✓ Test 1 - Splat forwarding to regular method: works
✓ Test 2 - Data.define without splat forwarding: works
✗ Test 3 - Data.define with both splats: ArgumentError: wrong number of arguments (given 1, expected 0)
✓ Test 4 - Data.define with only *args: works
Summary
The error occurs specifically when:
- A method has BOTH *args AND **kwargs parameters (even when kwargs is empty)
- That method calls a Data.define (or Struct) constructor with new(*args, **kwargs)
Important notes:
- Splat forwarding works fine with regular methods (Test 1)
- Data.define works fine without splat forwarding (Test 2)
- Data.define works fine with only *args (Test 4)
- Only the combination of both splats + Data.define/Struct fails (Test 3)
- Struct.new has the same issue although it causes ClassCastException instead of ArgumentError