Issue #21572 has been updated by Earlopain (Earlopain _). Thanks for opening this. It seems just like a normal though, no? I understand that this doesn't deviate from what parse.y does but it is a syntax error and right now consumers of prism simply accept such code. I guess there are tests in ruby/ruby that very specifically assert against this somehow? Other than that, is seems like an implementation detail. ---------------------------------------- Feature #21572: Make illegal variable in alternation pattern a syntax error https://bugs.ruby-lang.org/issues/21572#change-114625 * Author: kddnewton (Kevin Newton) * Status: Open ---------------------------------------- Currently when you have an illegal variable in an alternation pattern, you get a compile error, but no syntax error. ```ruby case foo in {a: } | Array "matched: #{a}" end ``` yields ``` $ ruby -cv test.rb ruby 3.5.0dev (2025-04-10T10:21:51Z master 756479324f) +PRISM [x86_64-linux] Syntax OK ``` but ``` $ ruby test.rb test.rb:2: illegal variable in alternative pattern (a) test.rb: compile error (SyntaxError) ``` Looking at the compiler, since illegal jumps (like break, next, etc.) are now syntax errors, the only other actual compiler errors are related to builtins. I think this should be a proper syntax error, so that editors and other tools can report on it and users can find it in development sooner. -- https://bugs.ruby-lang.org/