[ruby-core:116451] [Ruby master Bug#20213] zsuper with keyword splat without explicit keywords incorrectly uses mutable keyword splat

["jeremyevans0 (Jeremy Evans) via ruby-core" <ruby-core@ml.ruby-lang.org>]

Issue #20213 has been reported by jeremyevans0 (Jeremy Evans).

----------------------------------------
Bug #20213: zsuper with keyword splat without explicit keywords incorrectly uses mutable keyword splat
https://bugs.ruby-lang.org/issues/20213

* Author: jeremyevans0 (Jeremy Evans)
* Status: Open
* Priority: Normal
* Backport: 3.0: DONTNEED, 3.1: DONTNEED, 3.2: DONTNEED, 3.3: REQUIRED
----------------------------------------
As the subject states, the super call in this code is compiled incorrectly:

```ruby
extend(Module.new{def a(**k) k[:a] = 1 end})
extend(Module.new{def a(**k) p k; super; p k end})
a

# Expected output, actual output on Ruby 2.0-3.2:
{}
{}

# Actual output on Ruby 3.3 and master
{}
{:a=>1}
```

The zsuper call here uses VM_CALL_KW_SPLAT_MUT:

```
invokesuper                            <calldata!argc:1, FCALL|SUPER|ZSUPER|KW_SPLAT|KW_SPLAT_MUT>, nil
```

That is not correct, because as the example shows, if the super method accepts a keyword splat, the super method can modify the keyword splat, and changes are reflected in the caller.

I submitted a pull request to fix this: https://github.com/ruby/ruby/pull/9710, and marked this for backporting to 3.3.



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