[ruby-core:119485] [Ruby master Bug#20788] Prism issues unused variable warnings for negative line numbers

[ruby-core:119485] [Ruby master Bug#20788] Prism issues unused variable warnings for negative line numbers

[jeremyevans0 (Jeremy Evans) via ruby-core]

Issue #20788 has been reported by jeremyevans0 (Jeremy Evans).

----------------------------------------
Bug #20788: Prism issues unused variable warnings for negative line numbers
https://bugs.ruby-lang.org/issues/20788

* Author: jeremyevans0 (Jeremy Evans)
* Status: Open
* Assignee: kddnewton (Kevin Newton)
* Backport: 3.1: DONTNEED, 3.2: DONTNEED, 3.3: DONTNEED
----------------------------------------
parse.y does not issue unused variable warnings for negative line numbers. However, prism does issue such warnings.

Example code:

```ruby
Object.class_eval(<<END, nil, -2)
def a(locals)
  foo = locals[:foo]
  2
end
END
```

Output:

```
$ run_ruby -v --parser=prism --disable-gems t/t82.rb    
ruby 3.4.0dev (2024-10-08T22:14:44Z master 3fc1495c30) +PRISM [x86_64-openbsd7.6]
(eval at t/t82.rb:1):-1: warning: assigned but unused variable - foo

$ run_ruby -v --parser=parse.y --disable-gems t/t82.rb  
ruby 3.4.0dev (2024-10-08T22:14:44Z master 3fc1495c30) [x86_64-openbsd7.6]
```

This results in spurious verbose-mode warnings in applications using tilt, the template library used by most non-Rails web frameworks (Sinatra, Roda, Hanami, Cuba, Camping, etc.).



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