Bug #21713: Prism accepts pattern matching in modifier rescue followed by operators that shouldn't be allowed

• Status: Assigned
• Assignee: prism
• Target version: -
• ruby -v: ruby 4.0.0dev (2025-11-26T06:41:42Z master 43ed35de6c) +YJIT +MN +PRISM [arm64-darwin24]
• Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN

[tompng (tomoya ishida)]

These are syntax errors in parse.y but accepted in Prism

a rescue b => c in d
a rescue b in c..
a rescue b => c..
a rescue b => c::itself
a rescue b => c[]
a rescue b => c[0] = 1
a rescue b => c ? 1 : 2
a rescue b => c || 2

Found by this fuzzing script
https://gist.github.com/tompng/551777b9b850b0428c9062745cf763db

[mame (Yusuke Endoh)]

• Status changed from Open to Assigned
• Assignee set to prism