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Bug #11091

Updated by nobu (Nobuyoshi Nakada) about 2 years ago

See https://makandracards.com/makandra/32333-bugreport-symbolized-strings-break-keyword-arguments-in-ruby-2-2.

---
**TL;DR** Under certain circumstances, dynamically defined symbols may break keyword arguments in Ruby 2.2.

Specifically, **when** …


- there is a method with several keyword arguments **and** a double-splat argument (e.g. `def m(foo: 'bar, option: 'will be lost', **further_options)`)
- there is a dynamically created `Symbol` (e.g. `'culprit'.to_sym`) that is _created_ **before** the method is _parsed_
- the method gets called with both the `option` and a `culprit` keyword argument

… **then** the `option` keyword argument will be `nil` inside of `#m`.

## Affected Ruby Versions

- Affected version: 2.2.1, 2.2.2
- Unaffected versions: 1.x, 2.0, 2.1

## How to Expose it

The following code exposes the bug. Save it, make sure you have Ruby 2.2 and run it.

```ruby ```
test_symbol = '__test'

# The bug only occurs when a symbol used in a keyword argument is dynamically
# added to the Ruby symbols table *before* Ruby first sees the keyword argument.
existing = Symbol.all_symbols.map(&:to_s).grep('__test')
raise "Symbol #{test_symbol} already exists in symbol table!" if existing.any?

'__test'.to_sym # breaks it
# :__test # does not break it

# GC.start # fixes it

# Why #eval?
# Without, Ruby would parse the symbols in this code into its symbol table
# before running the file, which prevents the bug.
eval <<-RUBY
$hash = { __test: '__test', lost: 'lost', q: 'q' }

def _report(name, value)
puts name.to_s << ': ' << (value ? 'ok' : 'broken')
end

# Confirmed broken when:
# - `lost` is the second keyword argument Oo
# - there is a double-splat argument
def vulnerable_method_1(p: 'p', lost: 'lost', **options)
_report(__method__, lost)
end

def vulnerable_method_2(p: 'p', lost: 'lost', q: 'q', **options)
_report(__method__, lost)
end

def immune_method_1(lost: 'lost', p: 'p', **options)
_report(__method__, lost)
end

def immune_method_2(q: 'q', lost: 'lost', __test: '__test')
_report(__method__, lost)
end

def immune_method_3(lost: 'lost', **options)
_report(__method__, lost)
end
RUBY

# Exposure #####################################################################

puts '', 'Broken when calling with a hash'
vulnerable_method_1($hash)
vulnerable_method_2($hash)
immune_method_1($hash)
immune_method_2($hash)
immune_method_3($hash)

puts '', 'Double splat (**) has no influence:'
vulnerable_method_1(**$hash)
vulnerable_method_2(**$hash)
immune_method_1(**$hash)
immune_method_2(**$hash)
immune_method_3(**$hash)

puts '', 'Hash order does not matter:'
inversed_hash = Hash[$hash.to_a.reverse]
vulnerable_method_1(inversed_hash)
vulnerable_method_2(inversed_hash)
immune_method_1(inversed_hash)
immune_method_2(inversed_hash)
immune_method_3(inversed_hash)
```

## References

- Related (but does not fix it): [https://bugs.ruby-lang.org/issues/11027](https://bugs.ruby-lang.org/issues/11027)

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