Bug #21934: Prism and parse.y inconsistency in command call used with pattern match

• Status: Open
• Assignee: -
• Target version: -
• ruby -v: ruby 4.1.0dev (2026-03-03T16:19:28Z master e30b5a06dc) +PRISM [x86_64-linux]
• Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN

[tompng (tomoya ishida)]

These are syntax error in both parse.y and in Prism

a x in pattern
a x: in pattern
a &x in pattern
a *x => pattern
a x: => pattern
a &x => pattern

These are all syntax error in parse.y, all syntax valid in Prism

a.b x in pattern
a.b x: in pattern
a.b &x in pattern
a.b *x => pattern
a.b x: => pattern
a.b &x => pattern

I think this is related to https://github.com/ruby/prism/issues/3558, A.print message:\nin 'BAR' inside case-in was parsed as (A.print message:) in 'BAR'.