Issue #17426 has been reported by freiden (charles fd).

----------------------------------------
Bug #17426: method_missing can't override kernel#system method anymore
https://bugs.ruby-lang.org/issues/17426

* Author: freiden (charles fd)
* Status: Open
* Priority: Normal
* ruby -v: ruby 2.7.2p137 (2020-10-01 revision 5445e04352) [x86_64-darwin19]
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN
----------------------------------------
Hello,

It seems like I found a behavior change on the way method missing is working on Ruby 2.7.2 in comparison with 2.6.6.
`method_missing` can't intercept call to a method called `system`.

The following code help reproducing the behavior
```ruby
class Klass

  def method_missing(meth, *args, &blk)
    if %i[system foo].include?(meth)
      puts 'behavior not reproductible'
    else
      super
    end
  end

  # Work on 2.6.6
  def call_system_from_self
    self.system
  end

  # Doesn't work on both
  def call_system_from_implicit_self
    system
  end

  # Work on both
  def call_foo_from_self
    self.foo
  end

  # Work on both
  def call_foo_from_implicit_self
    foo
  end

  # Doesn't work on both
  def call_system_with_send_from_self
    self.send(:system)
  end

  # Work on both
  def call_foo_with_send_from_self
    self.send(:foo)
  end

  # Work on both
  def call_system_with_public_send
    self.public_send(:system)
  end

  # Work on both
  def call_foo_with_public_send
    self.public_send(:foo)
  end

end
```

Is it an expected behavior change in 2.7.2?




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