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Ruby New Added 9 October 2026

Ruby 3: ArgumentError: wrong number of arguments (given 2, expected 1)

Ruby 3.0 separated keyword arguments from positional ones, so a hash passed where a method expects keywords is now counted as an extra positional argument. Code that ran on Ruby 2.7, perhaps with a deprecation warning nobody read, fails after the upgrade. The usual places are wrappers that forward *args without **kwargs, and method_missing or define_method delegation.

Quick fix

Read the commands before running them. Anything that restarts a service, deletes data or changes permissions should be tried on a non-production system first.

Quick fix
# Ruby 2.7 warns at every affected call: run the suite there with warnings on
RUBYOPT='-W:deprecated' bundle exec rspec

# A hash passed to a method that takes keywords: splat it
def create(name, admin: false); end
opts = { admin: true }
create('sam', opts)     # Ruby 3: given 2, expected 1
create('sam', **opts)   # works

# Delegating wrappers must forward keywords too
def wrapper(*args, **kwargs, &blk) = target(*args, **kwargs, &blk)
# or, simplest
def wrapper(...) = target(...)

How to diagnose Ruby errors

Ruby errors are dominated by Bundler and gem resolution, native extension compilation (which needs system headers Ruby cannot install for you), and in Rails by the pending-migration and asset-precompilation guards. Those guards are deliberate safety checks, so the fix is to satisfy them rather than to disable them.

If the quick fix above does not resolve it, work through these steps. They apply to this whole class of error, not just to this one message, which is usually what saves the time.

  1. Run bundle install with verbose output and read which gem fails and why. Native extension failures name the missing header in the mkmf log.
  2. Check the mkmf log path the error prints. It contains the actual compiler error, which the Bundler summary truncates.
  3. For Rails migration errors, run rails db:migrate:status to see exactly which migrations the database has recorded.
  4. For asset errors in production, confirm rails assets:precompile ran during deployment and that the manifest is present in public/assets.
  5. Verify the Ruby version matches .ruby-version and the Gemfile. Version managers silently switch, producing gem-not-found errors for gems that are installed elsewhere.

Tools worth reaching for

  • bundle install --verbose
  • rails db:migrate:status
  • gem env
  • rbenv/rvm version check
  • bundle exec

Authoritative references

Primary documentation for this error, worth reading before applying any fix in production.

ruby-lang.org

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