Bug #20952: A weird error message for []= with keyword arguments

• Status: Closed
• Assignee: -
• Target version: -
• Backport: 3.1: DONTNEED, 3.2: DONTNEED, 3.3: DONTNEED

[zverok (Victor Shepelev)]

Trying to document the new deprecation of #[]= with keyword arguments, I wrote this sample code:

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]

[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)

[jeremyevans0 (Jeremy Evans)]

Same is true for block arguments:

$ ruby34 -c -e "matrix[5, &block] = 8"   
Syntax OK

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

[eightbitraptor (Matt V-H)]

• Status changed from Open to Closed

Applied in changeset git|e1946657205fb14583dd3020d60c5236a11fdd9b.

---

[PRISM] using []= to set kwargs is a syntax error

Fixes [Bug #20952]

[eightbitraptor (Matt V-H)]

• Status changed from Closed to Open

Re-Opening this in light of @jeremyevans0 (Jeremy Evans) comment about blocks

I merged the PR that addresses the kwargs issue at the same time as that comment was made.

[eightbitraptor (Matt V-H)]

• Status changed from Open to Closed

Applied in changeset git|b37777c36f6cb27d55f4fe44a95b3c970fbf9848.

---

[PRISM] Blocks are also a syntax error in array assignment

Actually close [Bug #20952]