Posted by Jaromir Matas on May 12, 2021; 6:48pm
URL: https://forum.world.st/stepping-over-non-local-return-in-a-protected-block-tp5128777p5129651.html

Hi Nicolas, Christoph, all

> When debugging things like this:
>
>   [^2] ensure: [Transcript cr; show: 'done'].
>
> if we step into the protected block [^2], then step over ^2, we
> incorrectly get a BlockCannotReturn.

Found a bug inside the debugger causing this problem: #stepOver uses
#runUntilErrorOrReturnFrom: which inserts an ensure context when started.
The problem happens when the debugger simulates #aboutToReturn:through: --
before it starts executing it via #runUntilErrorOrReturnFrom this method
inserts its ensure context between #aboutToReturn:through:firstUnwindContext
and its firstUnwindContext argument! This means the inserted context will be
skipped during execution and that's the whole problem :)

The situation is captured on the enclosed screenshot.
Screenshot_2021-05-12_202833.png
<http://forum.world.st/file/t372955/Screenshot_2021-05-12_202833.png>  

To prove this try changing #aboutToReturn and the BlockCannotReturn error is
gone:

#aboutToReturn: result through: firstUnwindContext
        "Called from VM when an unwindBlock is found between self and its home.
         Return to home's sender, executing unwind blocks on the way."

        self methodReturnContext return: result

I'm not sure how to fix it but a debugger pro should figure it out way
faster than me :)





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^[^ Jaromir
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