[ruby-core:102446] [Ruby master Bug#17619] if false foo=42; end creates a foo local variable set to nil

Issue #17619 has been updated by nobu (Nobuyoshi Nakada).

Status changed from Open to Rejected

In Ruby, local variables are defined by assignment expressions, and it is never in "undefined" state but is initialized as `nil`.


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Bug #17619: if false foo=42; end creates a foo local variable set to nil
https://bugs.ruby-lang.org/issues/17619#change-90330

* Author: pkmuldoon (Phil Muldoon)
* Status: Rejected
* Priority: Normal
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN
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Take this following code

```
[1] pry(main)> defined?(foo)
nil

[2] pry(main)> if false
[2] pry(main)*   foo = 42
[2] pry(main)* end  

[3] pry(main)> defined?(foo)
"local-variable"
```

The inner scope inherits the parent scope (ok) but also modifies the parent scope even if the child scope is never entered. A lesser effect of this:

```
[1] pry(main)> defined?(bar)
nil

[2] pry(main)> if false
[2] pry(main)*   bar = 99
[2] pry(main)* end  

[3] pry(main)> defined?(bar)
"local-variable"

[5] pry(main)> bar
99
```

That somewhat lesser affecting because I can just about accept a variable invading the parent scope, and existing after, as a hoisting event. But surely that should not be the case in the negative program-flow case?

The side effects of this are defined?(foo) can't be trusted anymore.

Apologies if this bug has been filed. I did search for it, but couldn't find anything quite matching it. Thanks!



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