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Prism accepts double wildcard with no required fields in pattern match #2915
Description
Slightly related to #2914
Prism parser the following code:
[1,2,3,4] => *a, *bThis results in a FindPatternNode with an empty list requireds.
MRI's parser rejects this syntax (I've tried this with Ruby 3.3.3 and a 3.4.0-dev of today):
ruby -e '[1,2,3,4] => *a, *b; p a; p b'
-e:1: syntax error, unexpected *
[1,2,3,4] => *a, *b; p a; p b
ruby: compile error (SyntaxError)
The behaviour is ambiguous: if we enable the prism parser in MRI, it turns out that the whole array is put into the right splat:
ruby --parser=prism -e '[1,2,3,4] => *a, *b; p a; p b'
ruby: warning: The compiler based on the Prism parser is currently experimental and compatibility with the compiler based on parse.y is not yet complete. Please report any issues you find on the `ruby/prism` issue tracker.
[]
[1, 2, 3, 4]
But the result a = [1, 2, 3, 4]; b = [] would have been just as valid. Other combinations like a = [1]; b = [2, 3, 4] would be valid too, but kind of random.
I would guess a FindPatternNode with no requireds should be a syntax error.
Activity
herwinw commentedon Jun 28, 2024
The same thing can happen with an
ArrayPatternNode:This too gets rejected by MRI
Switching the parser to Prism (ruby 3.4-dev, the default included prism 0.30) results in a segfault.
In this case, MRI even rejects syntax that I would think is not ambiguous:
This still results in a segfault when using
--parser=prismkddnewton commentedon Jun 28, 2024
Thanks @herwinw! I'll get these fixed
[Bug #21345] Fix accepting multiple rest patterns with leading match
[Bug #21345] Fix accepting multiple rest patterns with leading match
[Bug #21345] Fix accepting multiple rest patterns with leading match
[Bug #21345] Fix accepting multiple rest patterns with leading match
[ruby/prism] [Bug #21345] Fix accepting multiple rest patterns with l…