[ruby-core:120234] [Ruby master Bug#20952] A weird error message for []= with keyword arguments

Issue #20952 has been updated by jeremyevans0 (Jeremy Evans).


This is a bug in prism.  The expected behavior is parse.y's behavior of raising a syntax error:

```
$ ruby34 -c -e "matrix[5, axis: :y] = 8"                  
Syntax OK

$ ruby34 --parser=parse.y -c -e "matrix[5, axis: :y] = 8"
-e:1: keyword arg given in index assignment
matrix[5, axis: :y] = 8
ruby34: compile error (SyntaxError)
```

----------------------------------------
Bug #20952: A weird error message for []= with keyword arguments
https://bugs.ruby-lang.org/issues/20952#change-110999

* Author: zverok (Victor Shepelev)
* Status: Open
* Backport: 3.1: DONTNEED, 3.2: DONTNEED, 3.3: DONTNEED
----------------------------------------
Trying to document the new deprecation of `#[]=` with keyword arguments, I wrote this sample code:

```ruby
class MyMatrix
  # ...some implementation

  def []=(*args, **kwargs)
    p(args:, kwargs:)
    # ...some implementation
  end
end

matrix = MyMatrix.new
matrix[5, axis: :y] = 8
```

This fails as expected, but the error message is totally unexpected for me:
```
ruby3_4.rb:11:in '<main>': undefined method '[]=' for an instance of Integer (NoMethodError)

matrix[5, axis: :y] = 8
      ^^^^^^^^^^^^^^^
```

Am I missing some interpretation peculiarity here?..

```
$ ruby -v
ruby 3.4.0dev (2024-12-11T19:50:20Z master 34e68548d4) +PRISM [x86_64-linux]
```



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