<div dir="ltr">Gosh, I accidentally fixed it in Squeak !7 years before it was even noticed...<br><a href="https://source.squeak.org/trunk/Kernel-nice.346.diff">https://source.squeak.org/trunk/Kernel-nice.346.diff</a></div><br><div class="gmail_quote gmail_quote_container"><div dir="ltr" class="gmail_attr">Le lun. 5 oct. 2026 à 22:16, Juan Vuletich via Cuis-dev <<a href="mailto:cuis-dev@lists.cuis.st">cuis-dev@lists.cuis.st</a>> a écrit :<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><u></u>
<div>
<p>Hi Facu,</p>
<p>Wow! Not every day you find a bug that is over 40 years old!</p>
<p>Just pushed this to GitHub. Thanks!</p>
<p>Cheers,</p>
<div>On 2026-10-04 1:01 PM, Facundo Javier
Gelatti via Cuis-dev wrote:<br>
</div>
<blockquote type="cite">
<div dir="ltr">
<div>Hello!</div>
<div><br>
</div>
<div>This is a bug report + fix.</div>
<div><br>
</div>
<div>The bug is the following: declaring a class instance
variable from the "Unknown variable" popup sometimes produces
a method whose bytecode does not match the source (it stores
into the wrong variables).</div>
<div>I attach some code to see this (<span style="font-family:monospace"><a href="http://example.workspace.st" target="_blank">example.workspace.st</a></span>),
which should be run from a workspace.</div>
<div><br>
</div>
<div>This happens because <span style="font-family:monospace">Metaclass>>addInstVarName:</span>
reverses the order of existing variables (which is already a
weird behavior), and the compiler resolves instance variables
to slot numbers at the start of the compilation. So, in an
interactive environment:</div>
<div>1. When we accept a method with an undeclared name, a
notification is signalled mid-compilation.</div>
<div>2. Then, from the popup, we choose to declare an instance
variable.</div>
<div>3. So, <span style="font-family:monospace">Parser>>declareInstVar:</span>
sends <span style="font-family:monospace">#addInstVarName:</span>.
This adds the instance variable (reversing the order of the
existing ones), and triggers a recompilation of all existing
methods (this does not include the method mid-compilation,
which is not yet installed on the class).</div>
<div>4. Then the compilation resumes. But the encoder has
already assigned a slot index to every pre-existing variable,
so the system ends up producing the wrong bytecode.</div>
<div>Note that the class needs to have at least two existing
class instance variables for this to happen (since reversing
just one does nothing).</div>
<div><br>
</div>
<div>The fix is to make <span style="font-family:monospace">Metaclass>>addInstVarName:</span> preserve
the order of the variables (as <span style="font-family:monospace">Class>>addInstVarName:</span>
already does). With the order preserved, the indices the
encoder computed before the declaration stay valid.</div>
<div><br>
</div>
<div>I've included tests for the bug, and also two additional
things for consistency: one test for this same thing but
instance-side, and a change to <span style="font-family:monospace">#removeInstVarName:</span> to
also preserve the order of the variables (removing class
instance variables does not produce wrong behavior, but it is
a bit confusing to see the order of the variables change).</div>
<div><br>
</div>
<div style="text-align:center">* * *</div>
<div><br>
</div>
<div>As a side-note: I've been chasing this bug for some time,
since it specially affected students using Cuis-University
(denotative objects are classes behind the scenes, so all
instance variables are class instance variables). The bug was
hard to find because when you recompile the method (e.g. make
any change and recompile, or file it out and then file it in,
etc.), the bytecode is silently fixed.</div>
<div><br>
</div>
<div>Cheers!</div>
<div>Facu</div>
</div>
<br>
<fieldset></fieldset>
</blockquote>
<pre cols="72">--
Juan Vuletich
<a href="http://www.cuis.st" target="_blank">www.cuis.st</a>
<a href="http://github.com/jvuletich" target="_blank">github.com/jvuletich</a>
<a href="http://researchgate.net/profile/Juan-Vuletich" target="_blank">researchgate.net/profile/Juan-Vuletich</a>
<a href="http://independent.academia.edu/JuanVuletich" target="_blank">independent.academia.edu/JuanVuletich</a>
<a href="http://patents.justia.com/inventor/juan-manuel-vuletich" target="_blank">patents.justia.com/inventor/juan-manuel-vuletich</a></pre>
</div>
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