Fix unexpected error when or-asgn/and-asgn

lib/steep/type_construction.rb

@@ -2275,13 +2275,10 @@ def synthesize(node, hint: nil, condition: false)
               type, constr = synthesize(rhs, hint: hint)
               constr.ivasgn(asgn, type)
             when :send
-              rhs_ = node.updated(:send,
-                                  [
-                                    asgn.children[0],
-                                    :"#{asgn.children[1]}=",
-                                    asgn.children[2],
-                                    rhs
-                                  ])
+              children = asgn.children.dup
+              children[1] = :"#{children[1]}="
+              send_arg_nodes = [*children, rhs]
+              rhs_ = node.updated(:send, send_arg_nodes)
               node_type = case node.type
                           when :or_asgn
                             :or

test/type_construction_test.rb

@@ -2083,6 +2083,41 @@ def test_or_and_asgn
     end
   end
 
+  def test_or_and_asgn_method
+    with_checker(<<-RBS) do |checker|
+class OrAndAsgn
+  def or_asgn: () -> Integer
+  def and_asgn: () -> Integer
+  def var=: (Integer) -> Integer
+end
+RBS
+      source = parse_ruby(<<-'EOF')
+class OrAndAsgn
+  def or_asgn
+    self.var ||= 1
+  end
+
+  def and_asgn
+    self.var &&= 2
+  end
+
+  def var=(a)
+    a
+  end
+end
+EOF
+
+      with_standard_construction(checker, source) do |construction, typing|
+        construction.synthesize(source.node)
+        assert_equal 2, typing.errors.size
+        assert_all typing.errors do |error|
+          assert_equal :var, error.method
+          error.is_a?(Diagnostic::Ruby::NoMethod)
+        end
+      end
+    end
+  end
+
   def test_next
     with_checker do |checker|
       source = parse_ruby(<<-'EOF')