From 780d193b113002232e98c1dd4b30f87709e50eb3 Mon Sep 17 00:00:00 2001
From: Takumi Shotoku <sinsoku.listy@gmail.com>
Date: Sat, 5 Sep 2026 17:47:37 +0900
Subject: [PATCH] Fix nested destructuring after a splat in multiple assignment

MultiWriteNode#install0 collected the targets after the splat by their
own `ret` instead of the vertex behind their DummyRHSNode. A nested
target (MultiTargetNode) has a nil `ret`, which blew up as the
destination of a graph edge in the next reinstall. The same mistake hit
an index or attribute writer silently: it got the return vertex of its
own call, so the assigned value never reached it.

    *a, (b, c) = 1, 2, [3, 4]
    #=> undefined method 'on_type_added' for nil
---
 lib/typeprof/core/ast/misc.rb               |  2 +-
 scenario/variable/masgn_nested.rb           | 30 +++++++++++++++++++
 scenario/variable/masgn_rest_then_writer.rb | 33 +++++++++++++++++++++
 3 files changed, 64 insertions(+), 1 deletion(-)
 create mode 100644 scenario/variable/masgn_rest_then_writer.rb

diff --git a/lib/typeprof/core/ast/misc.rb b/lib/typeprof/core/ast/misc.rb
index 56f0321e0..ed1d52e6c 100644
--- a/lib/typeprof/core/ast/misc.rb
+++ b/lib/typeprof/core/ast/misc.rb
@@ -126,7 +126,7 @@ def install0(genv)
         if @rights
           @rights.each {|lhs| lhs.install(genv) }
           @rights.each {|lhs| lhs.rhs.ret || raise(lhs.rhs.inspect) }
-          rights = @rights.map {|rhs| rhs.ret }
+          rights = @rights.map {|lhs| lhs.rhs.ret }
         end
 
         box = @changes.add_masgn_box(genv, value, lefts, rest_elem, rights)
diff --git a/scenario/variable/masgn_nested.rb b/scenario/variable/masgn_nested.rb
index ae81c7d74..bf6849864 100644
--- a/scenario/variable/masgn_nested.rb
+++ b/scenario/variable/masgn_nested.rb
@@ -24,6 +24,31 @@ def test_nested_with_rest_and_rights
   [a, b, rest, c]
 end
 
+def test_rest_then_nested
+  *a, (b, c) = [1, 2, [3, 4]]
+  [a, b, c]
+end
+
+def test_rest_then_nested_and_right
+  *a, (b, c), d = [1, ["str", :sym], 2.0]
+  [a, b, c, d]
+end
+
+def test_rest_then_deeper_nesting
+  *a, (b, (c, d)) = [1, [2, [3, 4]]]
+  [a, b, c, d]
+end
+
+def test_rest_then_nested_with_rest
+  *a, (b, *rest) = [1, [2, 3, 4]]
+  [a, b, rest]
+end
+
+def test_rest_then_nested_generic
+  *a, (b, c) = [[1, 2], [3, 4]].map {|x| x }
+  [a, b, c]
+end
+
 ## assert
 class Object
   def test_nested_destructuring: -> [Integer, Integer, Integer]
@@ -31,4 +56,9 @@ def test_nested_with_strings: -> [String, String, String]
   def test_deeper_nesting: -> [Integer, Integer, Integer, Integer]
   def test_nested_with_rest: -> [Integer, Integer, Array[Integer]]
   def test_nested_with_rest_and_rights: -> [Integer, Integer, Array[Integer], Integer]
+  def test_rest_then_nested: -> [Array[Integer], Integer, Integer]
+  def test_rest_then_nested_and_right: -> [Array[Integer], String, :sym, Float]
+  def test_rest_then_deeper_nesting: -> [Array[Integer], Integer, Integer, Integer]
+  def test_rest_then_nested_with_rest: -> [Array[Integer], Integer, Array[Integer]]
+  def test_rest_then_nested_generic: -> [Array[[Integer, Integer]], Integer, Integer]
 end
diff --git a/scenario/variable/masgn_rest_then_writer.rb b/scenario/variable/masgn_rest_then_writer.rb
new file mode 100644
index 000000000..41bfbe92f
--- /dev/null
+++ b/scenario/variable/masgn_rest_then_writer.rb
@@ -0,0 +1,33 @@
+## update: test.rb
+class C
+  def []=(i, v)
+    @v = v
+  end
+
+  def x=(v)
+    @x = v
+  end
+end
+
+def check(c)
+  *a, c[0], c.x = 1, 2, "str", :sym
+  a
+end
+
+def check_nested(c)
+  *a, (c[0], c.x) = 1, 2, ["str", :sym]
+  a
+end
+
+check(C.new)
+check_nested(C.new)
+
+## assert
+class C
+  def []=: (Integer, String) -> String
+  def x=: (:sym) -> :sym
+end
+class Object
+  def check: (C) -> Array[Integer]
+  def check_nested: (C) -> Array[Integer]
+end