[ruby-core:120369] [Ruby master Bug#20965] `it` vs `binding.local_variables`

Issue #20965 has been updated by mame (Yusuke Endoh).

Status changed from Closed to Open

Let's revert this change.

Below is our local discussion of this issue with @nobu and @ko1.

First, consider the following example.

```ruby
"foo".tap do
  it
  "bar".tap do
    p eval("it") # what should happen?
  end
end
```

There are three possible options.

1. Raises an exeption
2. Returns `"bar"`
3. Returns `"foo"`

1 is the only realistic choice. 2 would require keeping all arguments conservatively even when `it` does not appear lexically, which we want to avoid for a performance reason (including the possibility of future optimizations, as @ko1 said). 3 is clearly counterintuitive.

Then, consider the following example.

```ruby
"foo".tap do
  it
  "bar".tap do
    p binding.local_variables #=> []? [:it]?
    eval("it")
  end
end
```

If `local_variables` contains `:it`, `eval("it")` is expected to return some value. However, it is impossible for the reason above. Therefore, `local_variables` should return `[]`.

The difference between `_1` and `it` is that `_1` is prohibited to be referenced outside of a block, while `it` is not.

Note that if `it` is defined as an ordinary local variable by an assignment, `local_variables` should contain `:it`.

----------------------------------------
Bug #20965: `it` vs `binding.local_variables`
https://bugs.ruby-lang.org/issues/20965#change-111145

* Author: zverok (Victor Shepelev)
* Status: Open
* ruby -v: ruby 3.4.0dev (2024-12-15T13:36:38Z master 366fd9642f) +PRISM [x86_64-linux]
* Backport: 3.1: DONTNEED, 3.2: DONTNEED, 3.3: DONTNEED
----------------------------------------
`it` is not available in the list of `binding.local_varaibles`, **unlike** numbered parameters:

```ruby
p(proc { binding.local_variables }.call)  # []
p(proc { |x| binding.local_variables }.call)  # [:x]
p(proc { _1; binding.local_variables }.call)  # [:_1]
p(proc { vars = binding.local_variables; _1; vars }.call)  # [:_1, :vars]
p(proc { it; binding.local_variables }.call)  # []
```

I wonder if it is deliberate or accidental.



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