Bug #20784: `?\` followed by EOF is parsed wrong

• Status: Open
• Assignee: -
• Target version: -
• ruby -v: ruby -v: ruby 3.4.0dev (2024-10-05T02:36:21Z master e939f28cc9) +YJIT +MN +PRISM [arm64-darwin22]
• Backport: 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN

[tompng (tomoya ishida)]

?\ at EOF should be syntax error

% printf "p ?\\" | ruby --parser=parse.y
[nothing shown]

% printf "1 in a ?\\" | ruby --parser=parse.y -c
Syntax OK

With --parser=prism, ?\ at EOF is parsed as empty string, reported in https://github.com/ruby/prism/issues/3144

[tompng (tomoya ishida)]

https://github.com/ruby/ruby/pull/11805