Why is the behaviour of begin-next-end different in ruby and jruby?

Question

Compare the following scenarios (they are the same, but the outcome is different):

First I'll do it on ruby (cruby)

~> irb
irb(main):001:0> begin
irb(main):002:1* begin
irb(main):003:2* puts 1
irb(main):004:2> next
irb(main):005:2> end
irb(main):006:1> puts 2
irb(main):007:1> end
SyntaxError: (irb):4: Can't escape from eval with next

Now same thing on jruby:

~> jirb
irb(main):001:0> begin
irb(main):002:1* begin
irb(main):003:2* puts 1
irb(main):004:2> next
irb(main):005:2> end
irb(main):006:1> puts 2
irb(main):007:1> end
1
=> nil

Why doesn't this fail on jruby like it does on cruby? Is this a jruby bug?

Answer 1

Around the Ruby 1.9 timeframe, MRI started to detect some of these illegal jump cases at parse time rather than raising LocalJumpError. JRuby, MRuby, and Rubinius likely still leave the jump in place and let it fail later on when invoked rather than raising a Syntax error right away.

It might be worth filing a bug with JRuby. Our parser is basically a port of MRIs so we should be able to raise the same error. Barring that, we can perform this analysis at compile time and raise the error then.

Answer 2

I filed this as Bug #13064.

I tested your code in a variety of versions of YARV, as well as on the latest versions of JRuby, MRuby, and Rubinius:

• YARV 2.2.0 (the build shipping with macOS)

  # ruby -v -W -e 'begin; begin puts 1; next end; puts 2 end'
  ruby 2.0.0p648 (2015-12-16 revision 53162) [universal.x86_64-darwin16]
  -e:1: warning: statement not reached
  -e:1: Invalid next
  -e: compile error (SyntaxError)
  
  # irb -f -d -w -W
  irb(main):001:0> p RUBY_VERSION
  "2.0.0"
  => "2.0.0"
  irb(main):002:0> p RUBY_ENGINE
  "ruby"
  => "ruby"
  irb(main):003:0> 
  irb(main):004:0* begin
  irb(main):005:1*   begin
  irb(main):006:2*     puts 1
  irb(main):007:2>     next
  irb(main):008:2>   end
  irb(main):009:1>   puts 2
  irb(main):010:1> end
  (irb):9: warning: statement not reached
  Exception `SyntaxError' at /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/irb/workspace.rb:86 - (irb):7: Can't escape from eval with next
  Exception `SyntaxError' at /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/irb/workspace.rb:86 - (irb):7: Can't escape from eval with next
  SyntaxError: (irb):7: Can't escape from eval with next
      from (irb)
  irb(main):011:0> 
  irb(main):012:0* exit
  

• YARV 2.3.1 (the version JRuby claims to be compatible with at the moment)

  # ruby -v -W -e 'begin; begin puts 1; next end; puts 2 end'
  ruby 2.3.1p112 (2016-04-26 revision 54768) [x86_64-darwin16]
  -e:1: warning: statement not reached
  -e: -e:1: Invalid next (SyntaxError)
  
  # irb -f -d -w -W
  irb(main):001:0> p RUBY_VERSION
  "2.3.1"
  => "2.3.1"
  irb(main):002:0> p RUBY_ENGINE
  "ruby"
  => "ruby"
  irb(main):003:0> 
  irb(main):004:0* begin
  irb(main):005:1*   begin
  irb(main):006:2*     puts 1
  irb(main):007:2>     next
  irb(main):008:2>   end
  irb(main):009:1>   puts 2
  irb(main):010:1> end
  (irb):9: warning: statement not reached
  Exception `SyntaxError' at /Users/joerg/.rbenv/versions/2.3.1/lib/ruby/2.3.0/irb/workspace.rb:87 - (irb):7: Can't escape from eval with next
  Exception `SyntaxError' at /Users/joerg/.rbenv/versions/2.3.1/lib/ruby/2.3.0/irb/workspace.rb:87 - (irb):7: Can't escape from eval with next
  Exception `SyntaxError' at /Users/joerg/.rbenv/versions/2.3.1/lib/ruby/2.3.0/irb/workspace.rb:87 - (irb):7: Can't escape from eval with next
  SyntaxError: (irb):7: Can't escape from eval with next
      from (irb)
  irb(main):011:0> 
  irb(main):012:0* exit
  

• YARV 2.3.3

  # ruby -v -W -e 'begin; begin puts 1; next end; puts 2 end'
  ruby 2.3.3p222 (2016-11-21 revision 56859) [x86_64-darwin16]
  -e:1: warning: statement not reached
  -e: -e:1: Invalid next (SyntaxError)
  
  # irb -f -d -w -W
  irb(main):001:0> p RUBY_VERSION
  "2.3.3"
  => "2.3.3"
  irb(main):002:0> p RUBY_ENGINE
  "ruby"
  => "ruby"
  irb(main):003:0> 
  irb(main):004:0* begin
  irb(main):005:1*   begin
  irb(main):006:2*     puts 1
  irb(main):007:2>     next
  irb(main):008:2>   end
  irb(main):009:1>   puts 2
  irb(main):010:1> end
  (irb):9: warning: statement not reached
  Exception `SyntaxError' at /Users/joerg/.rbenv/versions/2.3.3/lib/ruby/2.3.0/irb/workspace.rb:87 - (irb):7: Can't escape from eval with next
  Exception `SyntaxError' at /Users/joerg/.rbenv/versions/2.3.3/lib/ruby/2.3.0/irb/workspace.rb:87 - (irb):7: Can't escape from eval with next
  Exception `SyntaxError' at /Users/joerg/.rbenv/versions/2.3.3/lib/ruby/2.3.0/irb/workspace.rb:87 - (irb):7: Can't escape from eval with next
  SyntaxError: (irb):7: Can't escape from eval with next
      from (irb)
  irb(main):011:0> 
  irb(main):012:0* exit
  

• YARV 2.4.0-preview3:

  # ruby -v -W -e 'begin; begin puts 1; next end; puts 2 end'
  ruby 2.4.0preview3 (2016-11-07 trunk 56661) [x86_64-darwin16]
  -e:1: warning: statement not reached
  -e: -e:1: Invalid next (SyntaxError)
  
  # irb -f -d -w -W
  irb(main):001:0> p RUBY_VERSION
  "2.4.0"
  => "2.4.0"
  irb(main):002:0> p RUBY_ENGINE
  "ruby"
  => "ruby"
  irb(main):003:0> 
  irb(main):004:0* begin
  irb(main):005:1*   begin
  irb(main):006:2*     puts 1
  irb(main):007:2>     next
  irb(main):008:2>   end
  irb(main):009:1>   puts 2
  irb(main):010:1> end
  (irb):9: warning: statement not reached
  Exception `SyntaxError' at /Users/joerg/.rbenv/versions/2.4.0-preview3/lib/ruby/2.4.0/irb/workspace.rb:87 - (irb):7: Can't escape from eval with next
  SyntaxError: (irb):7: Can't escape from eval with next
      from (irb)
  irb(main):011:0> 
  irb(main):012:0* exit
  

• YARV 2.4.0-dev (current SVN trunk as of yesterday):

  # ruby -v -W -e 'begin; begin puts 1; next end; puts 2 end'
  ruby 2.4.0dev (2016-12-22 trunk 57151) [x86_64-darwin16]
  -e:1: warning: statement not reached
  -e: -e:1: Invalid next (SyntaxError)
  
  # irb -f -d -w -W
  irb(main):001:0> p RUBY_VERSION
  "2.4.0"
  => "2.4.0"
  irb(main):002:0> p RUBY_ENGINE
  "ruby"
  => "ruby"
  irb(main):003:0> 
  irb(main):004:0* begin
  irb(main):005:1*   begin
  irb(main):006:2*     puts 1
  irb(main):007:2>     next
  irb(main):008:2>   end
  irb(main):009:1>   puts 2
  irb(main):010:1> end
  (irb):9: warning: statement not reached
  Exception `SyntaxError' at /Users/joerg/.rbenv/versions/2.4.0-dev/lib/ruby/2.4.0/irb/workspace.rb:87 - (irb):7: Can't escape from eval with next
  SyntaxError: (irb):7: Can't escape from eval with next
      from (irb)
  irb(main):011:0> 
  irb(main):012:0* exit
  

• Rubinius 3.69

  # rbx -v -W -e 'begin; begin puts 1; next end; puts 2 end'
  rubinius 3.69 (2.3.1 a57071c6 2016-11-17 3.8.1) [x86_64-darwin15.6.0]
  1
                  main # Rubinius::Loader at core/loader.rb:860
                 evals # Rubinius::Loader at core/loader.rb:646
                  eval # Kernel(Rubinius::Loader) at core/kernel.rb:1130
      call_on_instance # Rubinius::BlockEnvironment at core/block_environment.rb:147
     { } in __script__ # Object at -e:1
            jump_error . Rubinius at core/rubinius.rb:279
  
  invalid context for 'next' (LocalJumpError)
  
  An exception occurred evaluating command line code
  
  # irb
  irb(main):001:0> p RUBY_VERSION
  "2.3.1"
  => "2.3.1"
  irb(main):002:0> p RUBY_ENGINE
  "rbx"
  => "rbx"
  irb(main):003:0> 
  irb(main):004:0* begin
  irb(main):005:1*   begin
  irb(main):006:2*     puts 1
  irb(main):007:2>     next
  irb(main):008:2>   end
  irb(main):009:1>   puts 2
  irb(main):010:1> end
  1
  LocalJumpError: invalid context for 'next'
      from core/rubinius.rb:279:in `jump_error'
      from (irb):7
      from core/block_environment.rb:147:in `call_on_instance'
      from core/kernel.rb:1130:in `eval'
      from core/kernel.rb:585:in `loop'
      from core/proc.rb:20:in `call'
      from core/kernel.rb:1067:in `catch'
      from core/throw_catch.rb:8:in `register'
      from core/kernel.rb:1066:in `catch'
      from core/proc.rb:20:in `call'
      from core/kernel.rb:1067:in `catch'
      from core/throw_catch.rb:8:in `register'
      from core/kernel.rb:1066:in `catch'
      from core/code_loader.rb:505:in `load_script'
      from core/code_loader.rb:590:in `load_script'
      from core/loader.rb:679:in `script'
      from core/loader.rb:861:in `main'irb(main):011:0> 
  irb(main):012:0* exit
  

• JRuby 9.1.6.0 (the latest release)

  # jruby -v -W -e 'begin; begin puts 1; next end; puts 2 end'
  jruby 9.1.6.0 (2.3.1) 2016-11-09 0150a76 Java HotSpot(TM) 64-Bit Server VM 25.102-b14 on 1.8.0_102-b14 +jit [darwin-x86_64]
  1
  LocalJumpError: unexpected next
    <main> at -e:1
  
  # irb -f -d -w -W
  irb(main):001:0> p RUBY_VERSION
  "2.3.1"
  => "2.3.1"
  irb(main):002:0> p RUBY_ENGINE
  "jruby"
  => "jruby"
  irb(main):003:0> 
  irb(main):004:0* begin
  irb(main):005:1*   begin
  irb(main):006:2*     puts 1
  irb(main):007:2>     next
  irb(main):008:2>   end
  irb(main):009:1>   puts 2
  irb(main):010:1> end
  1
  => nil
  irb(main):011:0> 
  irb(main):012:0* exit
  

• MRuby 1.2.0 (the minimal ISO compliant Ruby implementation written by matz himself)

  # mruby -v -e 'begin; begin puts 1; next end; puts 2 end'
  mruby 1.2.0 (2015-11-17) 
  00001 NODE_SCOPE:
  00001   NODE_BEGIN:
  00001     NODE_BEGIN:
  00001       NODE_BEGIN:
  00001         NODE_CALL:
  00001           NODE_SELF
  00001           method='puts' (383)
  00001           args:
  00001             NODE_INT 1 base 10
  00001         NODE_NEXT:
  00001       NODE_CALL:
  00001         NODE_SELF
  00001         method='puts' (383)
  00001         args:
  00001           NODE_INT 2 base 10
  irep 0x7fe0e3c1b630 nregs=4 nlocals=1 pools=1 syms=1 reps=0
  file: -e
      1 000 OP_LOADSELF   R1      
      1 001 OP_LOADI  R2  1   
      1 002 OP_SEND   R1  :puts   1
      1 003 OP_ERR    "unexpected next"
      1 004 OP_LOADSELF   R1      
      1 005 OP_LOADI  R2  2   
      1 006 OP_SEND   R1  :puts   1
      1 007 OP_STOP
  
  1
  trace:
      [0] -e:1
  LocalJumpError: unexpected next
  
  # irb -v
  mruby 1.2.0 (2015-11-17) 
  mirb - Embeddable Interactive Ruby Shell
  
  > p RUBY_VERSION
  00001 NODE_SCOPE:
  00001   NODE_BEGIN:
  00001     NODE_CALL:
  00001       NODE_SELF
  00001       method='p' (384)
  00001       args:
  00001         NODE_CONST RUBY_VERSION
  irep 0x7fceeac05220 nregs=4 nlocals=1 pools=0 syms=2 reps=0
  file: (mirb)
      1 000 OP_LOADSELF   R1      
      1 001 OP_GETCONST   R2  :RUBY_VERSION
      1 002 OP_SEND   R1  :p  1
      1 003 OP_STOP
  
  "1.9"
   => "1.9"
  > p RUBY_ENGINE
  00002 NODE_SCOPE:
  00002   NODE_BEGIN:
  00002     NODE_CALL:
  00002       NODE_SELF
  00002       method='p' (384)
  00002       args:
  00002         NODE_CONST RUBY_ENGINE
  irep 0x7fceeae05cf0 nregs=4 nlocals=1 pools=0 syms=2 reps=0
  file: (mirb)
      2 000 OP_LOADSELF   R1      
      2 001 OP_GETCONST   R2  :RUBY_ENGINE
      2 002 OP_SEND   R1  :p  1
      2 003 OP_STOP
  
  "mruby"
   => "mruby"
  > 
  00004 NODE_SCOPE:
  00004   NODE_BEGIN:
  irep 0x7fceeac06a50 nregs=2 nlocals=1 pools=0 syms=0 reps=0
  file: (mirb)
      4 000 OP_LOADNIL    R1      
      4 001 OP_STOP
  
   => nil
  > begin
  00005 NODE_NIL
  *   begin
  00007 NODE_NIL
  *     puts 1
  00009 NODE_NIL
  *     next
  00011 NODE_NIL
  *   end
  00013 NODE_NIL
  *   puts 2
  00015 NODE_NIL
  * end
  00012 NODE_SCOPE:
  00012   NODE_BEGIN:
  00012     NODE_BEGIN:
  00012       NODE_BEGIN:
  00012         NODE_CALL:
  00012           NODE_SELF
  00012           method='puts' (383)
  00012           args:
  00012             NODE_INT 1 base 10
  00013         NODE_NEXT:
  00015       NODE_CALL:
  00015         NODE_SELF
  00015         method='puts' (383)
  00015         args:
  00015           NODE_INT 2 base 10
  irep 0x7fceeae01130 nregs=4 nlocals=1 pools=1 syms=1 reps=0
  file: (mirb)
     12 000 OP_LOADSELF   R1      
     12 001 OP_LOADI  R2  1   
     12 002 OP_SEND   R1  :puts   1
     13 003 OP_ERR    "unexpected next"
     15 004 OP_LOADSELF   R1      
     15 005 OP_LOADI  R2  2   
     15 006 OP_SEND   R1  :puts   1
     15 007 OP_STOP
  
  1
  LocalJumpError: unexpected next
  > 
  00012 NODE_SCOPE:
  00012   NODE_BEGIN:
  irep 0x7fceeae078f0 nregs=2 nlocals=1 pools=0 syms=0 reps=0
  file: (mirb)
     12 000 OP_LOADNIL    R1      
     12 001 OP_STOP
  
   => nil
  > exit
  

What is most interesting is that MRuby, JRuby and Rubinius actually agree on the behavior, but differ from YARV. Either YARV or all the other ones are wrong. I cannot say which ones, though.