From: "jfi (James Inman) via ruby-core" <ruby-core@...>
Date: 2025-11-23T22:10:08+00:00
Subject: [ruby-core:123890] [Ruby Bug#21708] Ruby 3.4 Forwardable: setter delegations trigger SyntaxError from forwardable/impl.rb

Issue #21708 has been reported by jfi (James Inman).

----------------------------------------
Bug #21708: Ruby 3.4 Forwardable: setter delegations trigger SyntaxError from forwardable/impl.rb
https://bugs.ruby-lang.org/issues/21708

* Author: jfi (James Inman)
* Status: Open
* ruby -v: 3.4.7
* Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN
----------------------------------------
  - `forwardable`: 1.3.3 (bundled stdlib)
  - OS: Ubuntu 24.04 (also reproducible on macOS)
  - RUBYOPT / $DEBUG: default (but with $DEBUG=true or RUBYOPT=-d the errors are emitted)

# Reproduction Script (minimal)

```

  require "forwardable"

  class Host
    attr_accessor :scheme
  end

  class Delegator
    extend Forwardable
    def initialize
      @host = Host.new
    end
    def_delegator :@host, :scheme=, :scheme=
    def_delegator :@host, :scheme,  :scheme
  end

  $DEBUG = true # force forwardable to log the SyntaxError
  d = Delegator.new
  d.scheme = "https"
  puts d.scheme
```

Output running with `ruby -d`:

```
  Exception 'SyntaxError' at .../forwardable/impl.rb:6 - syntax errors found
  > 6 | BEGIN{throw tag}; ().scheme=
      |                    ^ expected an expression after `=`
```

Despite the `SyntaxError`, the program continues, but stderr is flooded whenever a setter is delegated. Similar errors appear for any delegated setter (`host=`, `port=`, etc.), causing noise in test runs and CI logs.

# Expected behavior

Delegating setter methods should not raise or log `SyntaxError`; `forwardable` should generate the delegator quietly, as in Ruby 3.3 and earlier.

# Other reports

  - ruby/forwardable issue #35 shows the same SyntaxError output pattern on Ruby 3.4: https://github.com/ruby/forwardable/issues/35



-- 
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