Fix RuntimeError on () as a method arg or hash splat value#445
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mame merged 1 commit intoruby:masterfrom Apr 28, 2026
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`CallBaseNode` and `HashNode` used `DummyNilNode` as a sentinel for anonymous rest forwarding (bare `*`) and anonymous keyword splat forwarding (bare `**`), checking via `is_a?(DummyNilNode)` at install time. Once empty parentheses `()` started producing `DummyNilNode` (via the parentheses_node unwrap in AST.create_node), passing `()` as a method argument or hash splat value was misinterpreted as anonymous forwarding, raising `RuntimeError: *anonymous_rest` or `**anonymous_keyword` from `LocalEnv#get_var`. Use plain `nil` as the placeholder for those forwarding cases instead, so `DummyNilNode` is reserved for actual nil-valued expressions. Also extend `scenario/misc/parens.rb` with cases where empty parens appear as an array element, an if condition, a method argument, a splatted argument, and a hash double-splat value. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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Summary
Follow-up to #441. After empty parentheses
()started producing aDummyNilNode, several call/hash sites began misinterpreting()as anonymous-forwarding syntax, raisingRuntimeError: *anonymous_restor**anonymous_keywordfromLocalEnv#get_var.Reproducers (all crash on current master):
Root cause
CallBaseNodeandHashNodewere overloadingDummyNilNodeas a sentinel for bare*/**forwarding. The placeholder created at parse time when the raw arg/value wasnil(the anonymous-forwarding case) was later detected withis_a?(DummyNilNode)at install time. Once()also became aDummyNilNode, the two cases collided.Reported by @sinsoku as the "separate issue" note in #441.
Fix
Use a plain
nilas the forwarding-placeholder in@positional_argsand@vals, and checkarg.nil?/val.nil?at install time.DummyNilNodeis then reserved for actual nil-valued expressions like(), with no semantic overlap.Test plan
scenario/misc/parens.rbextended with the new cases (also covers @sinsoku's other suggestions:[()]andif (); 1; end)rake testpasses (425 tests, 817 assertions)scenario/args/anonymous_rest.rb) still passes