[ruby-dev:51089] [Ruby master Bug#18069] `instance_exec` is just ignored when the block is originally a method

[info@ttanimichi.com]

Issue #18069 has been reported by ttanimichi (Tsukuru Tanimichi).

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Bug #18069: `instance_exec` is just ignored when the block is originally a method
https://bugs.ruby-lang.org/issues/18069

* Author: ttanimichi (Tsukuru Tanimichi)
* Status: Open
* Priority: Normal
* Backport: 2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN
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I know you can't `instance_exec` a proc which is generated by `Method#to_proc` because it has its original instance's context. But, in such a case, raising `ArgumentError` would be the ideal behavior.

```ruby
f = -> (x) { a + x }

class A
  def a
    1
  end
end

A.new.instance_exec(1, &f) # => 2

class B
  def b(x)
    a + x
  end
end

proc = B.new.method(:b).to_proc
A.new.instance_exec(1, &proc) # => undefined local variable or method `a' for #<B:0x00007fdaf30480a0> (NameError)
```



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