[ruby-core:79338] [Ruby trunk Bug#3841][Closed] RubyVM::InstructionSequence.to_a() and disasm() do not work properly for "for <var> in <list>"

Issue #3841 has been updated by Koichi Sasada.

Description updated
Status changed from Assigned to Closed

I'm not sure who fix this issue, but 2.5dev doesn't have this issue.

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Bug #3841: RubyVM::InstructionSequence.to_a() and disasm() do not work properly for "for <var> in <list>"
https://bugs.ruby-lang.org/issues/3841#change-62758

* Author: Sean O'Neil
* Status: Closed
* Priority: Normal
* Assignee: Koichi Sasada
* Target version: next minor
* ruby -v: ruby 1.9.2p0 (2010-08-18 revision 29036) [i386-mswin32_90]
* Backport: 2.2: UNKNOWN, 2.3: UNKNOWN, 2.4: UNKNOWN
----------------------------------------
 I have been playing with the concept of caching compiled Ruby instruction sequences and reloading them later. For now the simplest way to do it is to use RubyVM::InstructionSequence.to_a() and Marshal.dump() to convert the resulting array to a smaller binary byte sequence. While testing this, I found that some Ruby scripts worked fine when an instruction sequence was reloaded, but others broke.
 
 As a test, I decided to try compiling irb.rb and its dependencies. When I try to reload the compiled sequences, the first file that breaks is irb/extend-command.rb. I tracked it down to the way "for <vars> in <list>" code block and parameters are handled, but I am not sure how to fix it. When I converted each "for <vars> in <list>" loop to "<list>.each {|<vars>|", it started working perfectly. Here's an example of how the disassembly differs between the two loops:
 

```
 def self.install_extend_commands
   @EXTEND_COMMANDS.each {|args|
     def_extend_command(*args)
   }
 end
 == disasm: <RubyVM::InstructionSequence:block in install_extend_commands@irb/extend-command.rb>
 == catch table
 | catch type: redo   st: 0000 ed: 0012 sp: 0000 cont: 0000
 | catch type: next   st: 0000 ed: 0012 sp: 0000 cont: 0012
 |------------------------------------------------------------------------
 local table (size: 2, argc: 1 [opts: 0, rest: -1, post: 0, block: -1] s3)
 [ 2] args<Arg>  
 0000 trace            1                                               ( 110)
 0002 putnil           
 0003 getdynamic       args, 0
 0006 send             :def_extend_command, 1, nil, 10, <ic:0>
 0012 leave            
 
 def self.install_extend_commands
   for args in @EXTEND_COMMANDS
     def_extend_command(*args)
   end
 end
 == disasm: <RubyVM::InstructionSequence:block in install_extend_commands@irb/extend-command.rb>
 == catch table
 | catch type: redo   st: 0005 ed: 0016 sp: 0000 cont: 0005
 | catch type: next   st: 0005 ed: 0016 sp: 0000 cont: 0016
 |------------------------------------------------------------------------
 local table (size: 2, argc: 1 [opts: 0, rest: -1, post: 0, block: -1] s3)
 [ 2] ?<Arg>     
 0000 getdynamic       *, 0                                            ( 206)
 0003 setlocal         args                                            ( 204)
 0005 trace            1                                               ( 205)
 0007 putnil           
 0008 getlocal         args
 0010 send             :def_extend_command, 1, nil, 10, <ic:0>
 0016 leave            
```
 
 In this example, rb_id2name() returns NULL for the name of the argument passed to the code block. That is why it puts a "?" in the local table and a "*" in the getdynamic command. The to_a() method has a similar problem, and it appears to put a number there instead. When I use the load() method to convert the array back into an instruction sequence and try to execute it, the code block ends up receiving a number as a parameter instead of the entry in the list it is supposed to get.
 
 I imagine this is not a high priority for the Ruby core team, and I don't mind putting in some work to fix it. However, it looks like it would take me a while to figure out, so I would appreciate any tips you could give me to point me in the right direction.
 
 Thank you,
 Sean O'Neil




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