jruby 9.4.1.0 irb fails with a java backtrace when @

[suetanvil]

Environment information:

• Ubuntu 20.04 (Linux mica 5.15.0-60-generic #66~20.04.1-Ubuntu SMP Wed Jan 25 09:41:30 UTC 2023 x86_64 x86_64 x86_64 GNU/Linux)
• jruby 9.4.1.0 (3.1.0) 2023-02-07 237d5fa5f4 OpenJDK 64-Bit Server VM 16.0.1+9-Ubuntu-120.04 on 16.0.1+9-Ubuntu-120.04 +jit [x86_64-linux]
  ** (also on jruby 9.4.0.0 (3.1.0) 2022-11-23 95c0ec159f OpenJDK 64-Bit Server VM 16.0.1+9-Ubuntu-120.04 on 16.0.1+9-Ubuntu-120.04 +jit [x86_64-linux])
• openjdk version "16.0.1" 2021-04-20
• Installed via rbenv; no gems installed other than the defaults.
  ** (Well, for jruby 9.4.0.0; the 9.4.1.0 has a number of gems, but that's probably not relevant.)

Steps to reproduce:

1. Start irb with or without --noautocomplete
2. Type @ at the prompt. irb should fail with a JVM backtrace. This seems to happen regardless of where the @ is typed, outside of a string literal or comment.

Other details:

• jruby -e 'x = @y' seems to work as expected.
• The Ruby code used by the Emacs enh-ruby-mode package also exhibits this behaviour.

The Backtrace

Here's a partial backtrace:

[...]
INTERPRET_METHOD at org/jruby/internal/runtime/methods/MixedModeIRMethod.java:201
call at org/jruby/internal/runtime/methods/MixedModeIRMethod.java:188
call at org/jruby/internal/runtime/methods/DynamicMethod.java:220
cacheAndCall at org/jruby/runtime/callsite/CachingCallSite.java:495
call at org/jruby/runtime/callsite/CachingCallSite.java:244 [0/279]
processCall at org/jruby/ir/interpreter/InterpreterEngine.java:318
interpret at org/jruby/ir/interpreter/StartupInterpreterEngine.java:66
interpret at org/jruby/ir/interpreter/InterpreterEngine.java:82
INTERPRET_METHOD at org/jruby/internal/runtime/methods/MixedModeIRMethod.java:201
call at org/jruby/internal/runtime/methods/MixedModeIRMethod.java:188
call at org/jruby/internal/runtime/methods/DynamicMethod.java:220
cacheAndCall at org/jruby/runtime/callsite/CachingCallSite.java:495
call at org/jruby/runtime/callsite/CachingCallSite.java:244
processCall at org/jruby/ir/interpreter/InterpreterEngine.java:318
interpret at org/jruby/ir/interpreter/StartupInterpreterEngine.java:66
INTERPRET_ROOT at org/jruby/ir/interpreter/Interpreter.java:96
execute at org/jruby/ir/interpreter/Interpreter.java:81
execute at org/jruby/ir/interpreter/Interpreter.java:30
execute at org/jruby/ir/IRTranslator.java:42
runInterpreter at org/jruby/Ruby.java:1290
loadFile at org/jruby/Ruby.java:2964
load at org/jruby/runtime/load/LibrarySearcher.java:925
load at org/jruby/runtime/load/LibrarySearcher.java:883
load at org/jruby/runtime/load/LoadService.java:380
loadCommon at org/jruby/RubyKernel.java:1121
load at org/jruby/RubyKernel.java:1091
call at org/jruby/RubyKernel$INVOKER$s$load.gen:-1
call at org/jruby/internal/runtime/methods/JavaMethod.java:422
cacheAndCall at org/jruby/runtime/callsite/CachingCallSite.java:495
call at org/jruby/runtime/callsite/CachingCallSite.java:244
fcall at org/jruby/runtime/callsite/CachingCallSite.java:248
invokeOther11:load at home/chris/$_dot_rbenv/versions/jruby_minus_9_dot_4_dot_1_dot_0/bin//home/ch
ris/.rbenv/versions/jruby-9.4.1.0/bin/irb:23
RUBY$script at home/chris/$_dot_rbenv/versions/jruby_minus_9_dot_4_dot_1_dot_0/bin//home/ch
ris/.rbenv/versions/jruby-9.4.1.0/bin/irb:23
run at home/chris/$_dot_rbenv/versions/jruby_minus_9_dot_4_dot_1_dot_0/bin//home/ch
ris/.rbenv/versions/jruby-9.4.1.0/bin/irb:-1
invokeWithArguments at java/lang/invoke/MethodHandle.java:732
load at org/jruby/ir/Compiler.java:114
runScript at org/jruby/Ruby.java:1277
runNormally at org/jruby/Ruby.java:1194
runNormally at org/jruby/Ruby.java:1176
runNormally at org/jruby/Ruby.java:1212
runFromMain at org/jruby/Ruby.java:991
doRunFromMain at org/jruby/Main.java:398
internalRun at org/jruby/Main.java:282
run at org/jruby/Main.java:227
main at org/jruby/Main.java:199

The section between INTERPRET_METHOD sequences repeats, so I'm guessing this is an infinite recursion. However, I'm also attaching the full backtrace.

[suetanvil]

backtrace.txt.gz

Here's the full backtrace attached. Note that I had to copy-and-paste it into an editor in several steps so missing or duplicated lines are possible.

[headius]

This seems to be working on master, which will be 9.4.2:

irb(main):001:0> @
org/jruby/RubyKernel.java:1143:in `eval': (irb):1: `@' without identifiers is not allowed as an instance variable name (SyntaxError)
	from org/jruby/RubyKernel.java:1586:in `loop'
	from org/jruby/RubyKernel.java:1292:in `catch'
	from org/jruby/RubyKernel.java:1292:in `catch'
	from /home/headius/work/jruby/lib/ruby/gems/shared/gems/irb-1.4.2/exe/irb:11:in `<main>'
	from org/jruby/RubyKernel.java:1091:in `load'
	from /home/headius/work/jruby/bin/irb:23:in `<main>'

Probably some parser/ripper fixes by @enebo?

[headius]

Fixed already for #7639. Thanks for the report!