From d92e1e22f2de22ec5cfdad7987c13a04286fbdc8 Mon Sep 17 00:00:00 2001
From: Yusuke Endoh <mame@ruby-lang.org>
Date: Tue, 28 Apr 2026 22:25:48 +0900
Subject: [PATCH] Fix anonymous rest/keyword sentinel collision with empty
 parens

`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>
---
 lib/typeprof/core/ast/call.rb  |  4 ++--
 lib/typeprof/core/ast/value.rb |  4 ++--
 scenario/misc/parens.rb        | 33 +++++++++++++++++++++++++++++++++
 3 files changed, 37 insertions(+), 4 deletions(-)

diff --git a/lib/typeprof/core/ast/call.rb b/lib/typeprof/core/ast/call.rb
index de6a7e5f5..a2ddb1e31 100644
--- a/lib/typeprof/core/ast/call.rb
+++ b/lib/typeprof/core/ast/call.rb
@@ -37,7 +37,7 @@ def initialize(raw_node, recv, mid, mid_code_range, raw_args, last_arg, raw_bloc
               @splat_flags << false
             end
           end
-          @positional_args = args.map {|arg| arg ? AST.create_node(arg, lenv) : DummyNilNode.new(code_range, lenv) }
+          @positional_args = args.map {|arg| arg ? AST.create_node(arg, lenv) : nil }
 
           kw = @positional_args.last
           if kw.is_a?(TypeProf::Core::AST::HashNode) && kw.keywords
@@ -119,7 +119,7 @@ def install0(genv)
           keyword_args = forward_a_args.keywords
         else
           positional_args = @positional_args.map do |arg|
-            if arg.is_a?(DummyNilNode)
+            if arg.nil?
               @lenv.get_var(:"*anonymous_rest")
             else
               arg.install(genv)
diff --git a/lib/typeprof/core/ast/value.rb b/lib/typeprof/core/ast/value.rb
index a5cc282e2..a90e26f64 100644
--- a/lib/typeprof/core/ast/value.rb
+++ b/lib/typeprof/core/ast/value.rb
@@ -275,7 +275,7 @@ def initialize(raw_node, lenv, keywords)
             if raw_elem.value
               @vals << AST.create_node(raw_elem.value, lenv)
             else
-              @vals << DummyNilNode.new(code_range, lenv)
+              @vals << nil
             end
             @splat = true
           else
@@ -306,7 +306,7 @@ def install0(genv)
               all_symbol_keys = false
             end
           else
-            if val.is_a?(DummyNilNode)
+            if val.nil?
               h = @lenv.get_var(:"**anonymous_keyword")
             else
               h = val.install(genv)
diff --git a/scenario/misc/parens.rb b/scenario/misc/parens.rb
index 2c104f348..e40a56936 100644
--- a/scenario/misc/parens.rb
+++ b/scenario/misc/parens.rb
@@ -15,11 +15,38 @@ def with_default(x = ())
   x
 end
 
+def in_array
+  [()]
+end
+
+def in_condition
+  if (); 1; end
+end
+
+def take_arg(x); x; end
+
+def empty_as_arg
+  take_arg(())
+end
+
+def empty_as_splat_arg
+  take_arg(*())
+end
+
+def empty_as_kw_splat
+  { **() }
+end
+
 grouping
 nested
 empty
 with_default
 with_default(1)
+in_array
+in_condition
+empty_as_arg
+empty_as_splat_arg
+empty_as_kw_splat
 
 ## assert
 class Object
@@ -27,4 +54,10 @@ def grouping: -> Integer
   def nested: -> Integer
   def empty: -> nil
   def with_default: (?Integer?) -> Integer?
+  def in_array: -> [nil]
+  def in_condition: -> Integer?
+  def take_arg: (nil) -> nil
+  def empty_as_arg: -> nil
+  def empty_as_splat_arg: -> nil
+  def empty_as_kw_splat: -> Hash[untyped, untyped]
 end