Issue #21708 has been updated by byroot (Jean Boussier). Fix is here: https://github.com/ruby/forwardable/pull/39 ---------------------------------------- Bug #21708: Ruby 3.4 Forwardable: setter delegations trigger SyntaxError from forwardable/impl.rb https://bugs.ruby-lang.org/issues/21708#change-115297 * 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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