[ruby-core:119660] [Ruby master Bug#20856] Incorrect and inconsistent multi-thread eval execution

Issue #20856 has been updated by Eregon (Benoit Daloze).

Backport changed from 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN to 3.1: DONTNEED, 3.2: DONTNEED, 3.3: DONTNEED

It's a bug of 3.4.0-preview2 and specifically of the Prism compiler, 3.3 and earlier and `--parser=parse.y` succeed for all cases.

The order is:
* parse that file:
* execute it
* in that new thread eval is called
* that parses `"a == b"`, with outer scopes [[a,x], [s,b]].

----------------------------------------
Bug #20856: Incorrect and inconsistent multi-thread eval execution 
https://bugs.ruby-lang.org/issues/20856#change-110317

* Author: hurricup (Alexandr Evstigneev)
* Status: Open
* ruby -v: 3.4.0-preview2
* Backport: 3.1: DONTNEED, 3.2: DONTNEED, 3.3: DONTNEED
----------------------------------------
Consider example:
```
s = Thread.new {
  a = 5
  puts eval("a == b") 
  x = 6 
}
s.join
b = 11

```
As far as I see it, it should not work. Because at the moment of eval, b is unknown and not even declared (it can even be in condition).
But it may be available because file `iseq` already compiled and we know that there is b. 

So, this works in ruby 3.3 in a script we running, wrapped into the method, or required by other file.

But in 3.4-preview2: 
- it works in file
- it works in method
- it fails if required from other file with:
```
#<Thread:0x00007725530d6a98 /home/hurricup/Projects/ruby-debugger/rdi30/test2.rb:1 run> terminated with exception (report_on_exception is true):
(eval at /home/hurricup/Projects/ruby-debugger/rdi30/test2.rb:3):1:in 'block in <top (required)>': undefined local variable or method 'b' for main (NameError)
	from /home/hurricup/Projects/ruby-debugger/rdi30/test2.rb:3:in 'Kernel#eval'
	from /home/hurricup/Projects/ruby-debugger/rdi30/test2.rb:3:in 'block in <top (required)>'
(eval at /home/hurricup/Projects/ruby-debugger/rdi30/test2.rb:3):1:in 'block in <top (required)>': undefined local variable or method 'b' for main (NameError)
	from /home/hurricup/Projects/ruby-debugger/rdi30/test2.rb:3:in 'Kernel#eval'
	from /home/hurricup/Projects/ruby-debugger/rdi30/test2.rb:3:in 'block in <top (required)>'
```

And this ^^ is correct behavior if you ask me :) but atm it is inconsistent between the ruby versions and even in the scope of 3.4-preview2



-- 
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