Array#pack raises an internal exception when called with <L or >L

[postmodern]

I ran into an issue with Array#pack when trying to get my test suite passing on truffleruby-22.3.0. I was able to isolate the issue to calling Array#pack with <L or >L.

Steps To Reproduce

[0].pack('<L')

Expected Result

"\x00\x00\x00\x00"

Actual Result

truffleruby: an internal exception escaped out of the interpreter,
please report it to https://github.com/oracle/truffleruby/issues.

> (java.lang.UnsupportedOperationException)
	from org.truffleruby.core.format.pack.SimplePackParser.parse(SimplePackParser.java:429)
	from org.truffleruby.core.format.pack.PackCompiler.compile(PackCompiler.java:41)
	from org.truffleruby.core.array.ArrayNodes$PackNode.compileFormat(ArrayNodes.java:1614)
	from org.truffleruby.core.array.ArrayNodesFactory$PackNodeFactory$PackNodeGen.executeAndSpecialize(ArrayNodesFactory.java:7796)
	from org.truffleruby.core.array.ArrayNodesFactory$PackNodeFactory$PackNodeGen.execute(ArrayNodesFactory.java:7755)
	from org.truffleruby.language.RubyCoreMethodRootNode.execute(RubyCoreMethodRootNode.java:48)
(irb):2:in `pack'
	from (irb):2:in `<top (required)>'
	from /opt/rubies/truffleruby-22.3.0/lib/mri/irb/workspace.rb:116:in `evaluate'
	from /opt/rubies/truffleruby-22.3.0/lib/mri/irb/context.rb:450:in `evaluate'
	from /opt/rubies/truffleruby-22.3.0/lib/mri/irb.rb:567:in `block (2 levels) in eval_input'
	from /opt/rubies/truffleruby-22.3.0/lib/mri/irb.rb:751:in `signal_status'
	from /opt/rubies/truffleruby-22.3.0/lib/mri/irb.rb:548:in `block in eval_input'
	from /opt/rubies/truffleruby-22.3.0/lib/mri/irb/ruby-lex.rb:251:in `block (2 levels) in each_top_level_statement'
	from <internal:core> core/kernel.rb:407:in `loop'
	from /opt/rubies/truffleruby-22.3.0/lib/mri/irb/ruby-lex.rb:233:in `block in each_top_level_statement'
	from <internal:core> core/throw_catch.rb:36:in `catch'
	from /opt/rubies/truffleruby-22.3.0/lib/mri/irb/ruby-lex.rb:232:in `each_top_level_statement'
	from /opt/rubies/truffleruby-22.3.0/lib/mri/irb.rb:547:in `eval_input'
	from /opt/rubies/truffleruby-22.3.0/lib/mri/irb.rb:481:in `block in run'
	from <internal:core> core/throw_catch.rb:36:in `catch'
	from /opt/rubies/truffleruby-22.3.0/lib/mri/irb.rb:480:in `run'
	from /opt/rubies/truffleruby-22.3.0/lib/mri/irb.rb:409:in `start'
	from /opt/rubies/truffleruby-22.3.0/lib/gems/gems/irb-1.3.5/exe/irb:11:in `<top (required)>'
	from <internal:core> core/kernel.rb:376:in `load'
	from <internal:core> core/kernel.rb:376:in `load'
	from /opt/rubies/truffleruby-22.3.0/bin/irb:42:in `<main>'

Additional Information

• truffleruby 22.3.0, like ruby 3.0.3, GraalVM CE Native [x86_64-linux]

[eregon]

>/< should be suffixed according to docs: https://docs.ruby-lang.org/en/master/packed_data_rdoc.html#label-Modifiers+for+Integer+Directives

It seems a bug that CRuby accepts them before and in fact it seems to ignore them (!):

irb(main):007:0> RUBY_DESCRIPTION
=> "ruby 3.1.2p20 (2022-04-12 revision 4491bb740a) [x86_64-linux]"
irb(main):008:0> [1].pack('<L')
=> "\x01\x00\x00\x00"
irb(main):009:0> [1].pack('>L')
=> "\x01\x00\x00\x00"

irb(main):012:0> [1].pack('L<')
=> "\x01\x00\x00\x00"
irb(main):013:0> [1].pack('L>')
=> "\x00\x00\x00\x01"

TruffleRuby works fine with the correct L</L>.

So <L is a bug of the caller code, and probably a bug of CRuby too.
It would be great if you can report this to CRuby.

TruffleRuby should raise a proper Ruby exception though for this case, probably an ArgumentError.

[eregon]

As @andrykonchin found, there is actually a warning on CRuby with $VERBOSE=true:

$ ruby -v -e "p [0].pack('<L')"
ruby 3.1.2p20 (2022-04-12 revision 4491bb740a) [x86_64-linux]
<internal:pack>:144: warning: unknown pack directive '<' in '<L'
"\x00\x00\x00\x00"

Which seems somewhat related to https://bugs.ruby-lang.org/issues/19108.

[andrykonchin]

Fixed in e2940ef. Thank you for reporting!

The decision is to warn unconditionally in Ruby 3.2 and to raise an exception in the next Ruby version. The issue - https://bugs.ruby-lang.org/issues/19150.