Undefined values in objects cause ReferenceErrors through various operations #1916
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Thanks for this - I was a bit worried about this myself but the one-liner for #1691 seemed too good to pass up on :) This one especially looks big and is something I'm very surprised hasn't been found before. It seems like the solution may be to add a new variable type that causes a referenceerror when accessed, and to then use that in |
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I think fixing specifically the Btw the way ES handles this is by having the named reference be a pair of name and parent value, instead of name and child value. This way, the parent can't be freed until the reference is forced to a value. But the approach of introducing a new kind of var for ReferenceErrors sounds easier to integrate with existing code. What about just calling |
I'm not sure I understand? Because of the parsing, you get an ID, for instance |
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Ah, that makes sense. Thanks for explaining |
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Also seen with g.theme: http://forum.espruino.com/conversations/367936/#comment16178913 |
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Looks like this got mostly fixed. Would seem to still be a problem though |
Related: #1691
Investigating this a bit more, @djeis97 had an idea that this might be a bigger problem. Indeed, the following expression incorrectly raises a
ReferenceError:This is because
[undefined]is a temporary value, so it has no references.jspeFactorFunctionCallcorrectly evaluates this expression to a JsVar NAME whose varData is the integer 0, and whose firstChild isundefined([r1,l1] Name Integer 0 undefined). But at the end of that function, it unlocks the parent value, which in this case is the array[undefined].When
jsvUnLockunlocks this array, the array's lock count is 0, so its ref count becomes 0, so it is freed. This in turn decrements our name var's refcount to 0 ([r0,l1] Name Integer 0 undefined).Later,
jspParsecallsjsvCheckReferenceError, which sees[r0,l1] Name Integer 0 undefinedand treats it as a ReferenceError.Fundamentally, this seems to be an issue because
[r0,l_] Name _ undefinedare used both for indicating a ReferenceError, and for representing the reference obtained by indexing into an object with no references itself.Other examples of this error:
cc @kiranshila
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