[ruby-dev:51091] [Ruby master Feature#18069] `instance_exec` is just ignored when the block is originally a method

[merch-redmine@jeremyevans.net]

Issue #18069 has been updated by jeremyevans0 (Jeremy Evans).

Backport deleted (2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN)
Tracker changed from Bug to Feature

I don't think the current behavior is a bug. `Method#to_proc` is currently equivalent to:

```ruby
class Method
  def to_proc
    method = self
    ->(*args, **kwargs, &block) do
      method.call(*args, **kwargs, &block)
    end
  end
end
```

You wouldn't expect an `instance_exec` on that lambda to change the behavior of `Method#call`. So I think the current behavior is expected.

Note that it's not hard to change the behavior to raise an error in this case (and other cases like `module_exec`).  However, changing the behavior would result in significant backwards compatibility issues.  I tried a commit that raises ArgumentError in such a case: https://github.com/jeremyevans/ruby/commit/3e2db2f01281f2335c638142223f8b24531826bd.  However, it broke quite a few tests: https://github.com/jeremyevans/ruby/runs/3283493124. Some of the breakage may be due to implementation choice, but I checked and at least some of the breakage is unavoidable as the tests expect to pass procs created by `Method#to_proc` to `instance_exec` (e.g. `test_instance_exec_define_method_kwsplat`).

As I don't think this is a bug, I'm switching this to a feature request.

----------------------------------------
Feature #18069: `instance_exec` is just ignored when the block is originally a method
https://bugs.ruby-lang.org/issues/18069#change-93200

* Author: ttanimichi (Tsukuru Tanimichi)
* Status: Open
* Priority: Normal
----------------------------------------

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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