[ruby-core:120303] [Ruby master Bug#20965] `it` vs `binding.local_variables`

[ruby-core:120303] [Ruby master Bug#20965] `it` vs `binding.local_variables`

[zverok (Victor Shepelev) via ruby-core]

Issue #20965 has been reported by zverok (Victor Shepelev).

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

* Author: zverok (Victor Shepelev)
* Status: Open
* 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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[ruby-core:120308] [Ruby master Bug#20965] `it` vs `binding.local_variables`

[shan (Shannon Skipper) via ruby-core]

Issue #20965 has been updated by shan (Shannon Skipper).


It does seem like that last one should be `[:it]` for consistency if it wasn't intentional. +1

An aside, but it's also interesting that using `_2` causes `_1` to also be defined under Binding#local_variables.

``` ruby
proc { _9; local_variables }.call
# => [:_1, :_2, :_3, :_4, :_5, :_6, :_7, :_8, :_9]

proc { it; local_variables }.call
# => []
```


----------------------------------------
Bug #20965: `it` vs `binding.local_variables`
https://bugs.ruby-lang.org/issues/20965#change-111074

* 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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[ruby-core:120317] [Ruby master Bug#20965] `it` vs `binding.local_variables`

[nobu (Nobuyoshi Nakada) via ruby-core]

Issue #20965 has been updated by nobu (Nobuyoshi Nakada).


https://github.com/ruby/ruby/pull/12398

----------------------------------------
Bug #20965: `it` vs `binding.local_variables`
https://bugs.ruby-lang.org/issues/20965#change-111081

* 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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[ruby-core:120326] [Ruby master Bug#20965] `it` vs `binding.local_variables`

[tompng (tomoya ishida) via ruby-core]

Issue #20965 has been updated by tompng (tomoya ishida).


I have a concern of making `it` parameter an lvar.

~~~ruby
1| 42.tap do
2|   p binding.local_variable_get('it')
3|   it /1/i
4|   p it
5| end
~~~
When parser reads `p it` at line 4, `it` turns out to be a local variable, I think from the beginning of the block(from line 2).
But on line 3, `it /1/i` is already parsed as if lvar `it` does not exist.

It is impossible to re-parse the block again, so the original implementation(it parameter is not an lvar) makes sense to me.

----------------------------------------
Bug #20965: `it` vs `binding.local_variables`
https://bugs.ruby-lang.org/issues/20965#change-111096

* Author: zverok (Victor Shepelev)
* Status: Closed
* 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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[ruby-core:120369] [Ruby master Bug#20965] `it` vs `binding.local_variables`

[mame (Yusuke Endoh) via ruby-core]

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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[ruby-core:120372] [Ruby master Bug#20965] `it` vs `binding.local_variables`

[k0kubun (Takashi Kokubun) via ruby-core]

Issue #20965 has been updated by k0kubun (Takashi Kokubun).

Status changed from Closed to Open

Since fixing this raised issues like https://bugs.ruby-lang.org/issues/20970 (particularly relevant to this #20965) and it's too close to the release to design the behavior properly, we reverted https://github.com/ruby/ruby/pull/12398 for Ruby 3.4. 

----------------------------------------
Bug #20965: `it` vs `binding.local_variables`
https://bugs.ruby-lang.org/issues/20965#change-111149

* 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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[ruby-core:120374] [Ruby master Bug#20965] `it` vs `binding.local_variables`

[zverok (Victor Shepelev) via ruby-core]

Issue #20965 has been updated by zverok (Victor Shepelev).


Interestingly, numbered block parameters do this:

```ruby
"foo".tap do
  _1
  "bar".tap do
    p binding.local_variables #=> [_1]
    eval("_1") #  undefined local variable or method '_1' for main:Object (NameError)
  end
end
```

I am not saying this is good behavior, though. The things I am concerned about (after the release, of course):
1. Whatever the behavior is, it is deliberate and documented;
2. Whatever the behavior is, it is internally consistent (e.g., in #20955 the thing that surprised me was an inconsistency between proc and lambda);
3. Whatever the behavior is, I’d expect it to be as consistent as possible between `it` and numbered anonymous parameters.

(About the latter one: `it`s behavior, after the change is reverted, actually seems more internally consistent at least between `local_variables` and `eval`, so maybe numbered parameters should follow?)

----------------------------------------
Bug #20965: `it` vs `binding.local_variables`
https://bugs.ruby-lang.org/issues/20965#change-111151

* 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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[ruby-core:120375] [Ruby master Bug#20965] `it` vs `binding.local_variables`

[mame (Yusuke Endoh) via ruby-core]

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


I see. I think this is simply buggy.

```ruby
"foo".tap do
  _1
  "bar".tap do
    p binding.local_variable_get(:_1) #=> "foo"
  end
end
```

IMO, meta-programming APIs for numbered parameters and `it` should be separated from `binding#local_variable*` because they are not a local variable. It would be good to consider them towards 3.5.

----------------------------------------
Bug #20965: `it` vs `binding.local_variables`
https://bugs.ruby-lang.org/issues/20965#change-111152

* 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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[ruby-core:120574] [Ruby master Bug#20965] `it` vs `binding.local_variables`

[mame (Yusuke Endoh) via ruby-core]

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


We discussed this at the dev meeting. The above behavior of `p binding.local_variable_get(:_1)` is considered a bug.
Neither numbered parameters nor “it” should be considered as local variables. They should not be included in `binding#local_variables` or taken by `binding#local_variable_get`. I will do more research by implementing a patch and performing an experiment, and create a separate ticket.

----------------------------------------
Bug #20965: `it` vs `binding.local_variables`
https://bugs.ruby-lang.org/issues/20965#change-111400

* 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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