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[clean strict optional] Use dummy TypeInfo instead of None in Instance.type (and few more fixes) #3285

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Merged
merged 7 commits into from
Apr 30, 2017
Merged

[clean strict optional] Use dummy TypeInfo instead of None in Instance.type (and few more fixes) #3285

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0829d09
Use placeholder for Instance.type, clean fixup and subtypes
ilevkivskyi Apr 29, 2017
fcd53f3
Clean-up types
ilevkivskyi Apr 29, 2017
36c5182
Minor bugs with unrestricted variables
ilevkivskyi Apr 29, 2017
5bd0349
One more fix; and assert message
ilevkivskyi Apr 29, 2017
38ec0a6
Fix typo
ilevkivskyi Apr 29, 2017
469d523
Use AssertionError; add clarifying comment
ilevkivskyi Apr 30, 2017
a5c0958
Extend the FakeInfo comment explaining why None is not used.
ilevkivskyi Apr 30, 2017
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6 changes: 6 additions & 0 deletions mypy/nodes.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2215,6 +2215,12 @@ class FakeInfo(TypeInfo):
# Instance.type is set to NOT_READY. In the second step (in fixup.py) it is replaced by
# an actual TypeInfo. If you see the assertion error below, then most probably something
# went wrong during the second step and an 'Instance' that raised this error was not fixed.
# Note:
# 'None' is not used as a dummy value for two reasons:
# 1. This will require around 80-100 asserts to make 'mypy --strict-optional mypy'
# pass cleanly.
# 2. If NOT_READY value is accidentally used somewhere, it will be obvious where the value
# is from, whereas a 'None' value could come from anywhere.
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@gvanrossum gvanrossum Apr 30, 2017

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Excellent reasons!

def __getattr__(self, attr: str) -> None:
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@JukkaL JukkaL May 2, 2017

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@ilevkivskyi @gvanrossum This should probably be __getattribute__ instead. Now attributes defined in the body of TypeInfo will not trigger an AssertionError, as far as I know, and thus FakeInfo can mask some actual errors.

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@ilevkivskyi ilevkivskyi May 2, 2017

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In any case __getattribute__ looks more robust. Will make a PR soon.

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@gvanrossum gvanrossum May 2, 2017

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OK, but then I suspect that #3281 will come back. So we should at least have a test in place to verify it doesn't. (Because that's the kind of error that's being masked here -- and since in that particular case it was just getting the wrong full name of some type for some error message I'd rather have a poor error than a crash -- our users really don't like crashes.

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@ilevkivskyi ilevkivskyi May 2, 2017

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@gvanrossum
Yes, #3281 comes back, I tried your crash scenario and it indeed crashes (although in a different place). But it looks like Jukka's idea works! At least I have found two actual bugs in fixup.py, both related to metaclass de-serialization. After fixing those, your scenario from #3281 doe snot crash anymore. I will make a PR now so that you can try it.

raise AssertionError('De-serialization failure: TypeInfo not fixed')

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