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Re: [Help-smalltalk] ContextPart>>printOn: prints incorrect line
From: |
Ladislav Marek |
Subject: |
Re: [Help-smalltalk] ContextPart>>printOn: prints incorrect line |
Date: |
Fri, 15 Jul 2011 10:20:40 +0200 |
Thanks. Nice explanation.
On Fri, Jul 15, 2011 at 09:52, Paolo Bonzini <address@hidden> wrote:
> On 07/14/2011 08:25 PM, Ladislav Marek wrote:
>> I have observe strange behavior of MethodContext>>printOn: and
>> ContextPart>>currentLineInFile
>>
>> Eval [
>> thisContext print.
>> 1.
>> ]
>>
>> This code outputs: UndefinedObject>>executeStatements (test.st:3),
>> line is incorrect, I think it should be 2.
>>
>> Eval [
>> thisContext currentLineInFile printNl.
>> 1.
>> ]
>>
>> This code outputs: 2, as expected. I look at the
>> MethodContext>>printOn: method and there is
>> ContextPart>>currentLineInFile called, so why it outputs different
>> line number?
>
> It's an off-by-one error. This is the compiled bytecode for your first
> example:
>
> 0: source line 2
> push Global Variable[0] = ContextPart
> 2: send special message #thisContext
> 4: send selector 1, 0 args = #printNl
> 6: source line 2
> pop stack top
> 8: push 1
> return stack top
>
> The instruction pointer when sending #printNl is already 6. The call to
> #currentLineInFile prints erroneously takes the "source line" bytecode at
> address 6 into account, and prints 2+2-1 = 3.
>
> This patch fixes it:
>
> diff --git a/kernel/ContextPart.st b/kernel/ContextPart.st
> index bfcf8d5..dc11dd3 100644
> --- a/kernel/ContextPart.st
> +++ b/kernel/ContextPart.st
> @@ -125,7 +125,7 @@ methods that can be used in inspection or debugging.'>
> thus making the implementation faster."
>
> <category: 'debugging'>
> - ^self method sourceCodeMap at: self ip + 1 ifAbsent: [1]
> + ^self method sourceCodeMap at: self ip - 1 ifAbsent: [1]
> ]
>
> debugger [
>
> Thanks for reporting it!
>
> Paolo
>