为什么beginnextend在ruby和jruby中的行为不同？

比较以下场景（它们相同，但结果不同）：

首先，我将在ruby（cruby）上执行此操作

现在，jruby上的情况也一样：

~> 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

为什么jruby上没有像cruby上那样失败？这是一个jruby bug吗？

我将其归档为

我在YARV的各种版本以及JRuby、MRuby和Rubinius的最新版本中测试了您的代码：

• YARV 2.2.0（与macOS一起提供的构建）

• YARV 2.3.1（JRuby目前声称与兼容的版本）

• 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（截至昨天的当前SVN中继）：

• 鲁宾尼乌斯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（最新版本）

---

最有趣的是，MRuby、JRuby和Rubinius实际上同意这种行为，但与YARV不同。不是YARV就是所有其他人都错了。不过，我不能说是哪种情况。

在Ruby 1.9的时间框架内，MRI开始在解析时检测到一些非法跳转案例，而不是引发LocalJumpError。JRuby、MRuby和Rubinius可能仍然保留跳转，让它在稍后调用时失败，而不是立即引发语法错误

---

也许值得向JRuby提交一个bug。我们的解析器基本上是MRIs的一个端口，因此我们应该能够提出相同的错误。除此之外，我们可以在编译时执行此分析，然后提出错误。

另一种可能性可能是IRb的实现工件。众所周知，IRb的实现是黑客和脆弱的（慷慨地说），它的行为不一定与作为脚本运行的相同代码的行为相对应。一些更著名的不兼容性是顶级方法最终是公共的，即使它们应该是私有的，还有一些关于局部变量的奇怪之处。然而，控制流也存在一些差异，这不是不可能的。特别是，您的错误消息提到了

eval

，您甚至没有使用它……这似乎强烈地表明错误来自IRb本身的实现，而不是您的代码。感谢您的输入！当作为脚本运行时，行为确实不同：ruby:

无效下一步（SyntaxError）

和jruby:

LocalJumpError:unexpected下一步

我将其归档为。

# 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

# 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

# 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

# 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 -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 -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