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Don't crash when partial types are used in inherited attribute #6766

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Merged
merged 3 commits into from
May 13, 2019
Merged

Don't crash when partial types are used in inherited attribute #6766

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a180a1c
Fix
onlined May 5, 2019
e385932
Fix
onlined May 7, 2019
80d5a92
Update tests
onlined May 7, 2019
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10 changes: 8 additions & 2 deletions mypy/checker.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1786,7 +1786,6 @@ def check_assignment(self, lvalue: Lvalue, rvalue: Expression, infer_lvalue_type
infer_lvalue_type)
else:
lvalue_type, index_lvalue, inferred = self.check_lvalue(lvalue)

# If we're assigning to __getattr__ or similar methods, check that the signature is
# valid.
if isinstance(lvalue, NameExpr) and lvalue.node:
Expand All @@ -1803,7 +1802,9 @@ def check_assignment(self, lvalue: Lvalue, rvalue: Expression, infer_lvalue_type
else:
self.check_getattr_method(signature, lvalue, name)

if isinstance(lvalue, RefExpr):
# Defer PartialType's super type checking.
if (isinstance(lvalue, RefExpr) and
not (isinstance(lvalue_type, PartialType) and lvalue_type.type is None)):
if self.check_compatibility_all_supers(lvalue, lvalue_type, rvalue):
# We hit an error on this line; don't check for any others
return
Expand Down Expand Up @@ -1833,6 +1834,11 @@ def check_assignment(self, lvalue: Lvalue, rvalue: Expression, infer_lvalue_type
# Try to infer a partial type. No need to check the return value, as
# an error will be reported elsewhere.
self.infer_partial_type(lvalue_type.var, lvalue, rvalue_type)
# Handle None PartialType's super type checking here, after it's resolved.
if (isinstance(lvalue, RefExpr) and
self.check_compatibility_all_supers(lvalue, lvalue_type, rvalue)):
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The exception you added above removes the check for all kinds of partial types, while this only re-adds the check for partial None types. I don't say it is necessarily wrong, but I would at least add test cases with partial list and dict types (e.g. with an empty list in subclass that is subsequently gets an .append()).

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Yes, you are right. I will change the code, actually.

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Are you going to add the tests with an empty list in the subclass?

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I don't think I should add them anymore, because now I make the exception for only None partial types.

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But there may be a similar crash (or a regression later), I think it is better to have one in any case.

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@onlined onlined May 13, 2019 •
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I tried this on both master and this branch, it didn't give an error:

class A:
    x = ['a', 'b']

class B(A):
    x = []
    x.append(2)

I think it should give an error, but I could not be sure. What do you think? @ilevkivskyi

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@ilevkivskyi ilevkivskyi May 13, 2019 •
edited
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Yes, this should be an error. It looks like another consequence of #4547. Let's then merge this PR as is, and consider adding this test when #4547 is fixed. Could you please add a comment in that issue?

# We hit an error on this line; don't check for any others
return
elif (is_literal_none(rvalue) and
isinstance(lvalue, NameExpr) and
isinstance(lvalue.node, Var) and
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28 changes: 28 additions & 0 deletions test-data/unit/check-inference.test
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Original file line number Diff line number Diff line change
Expand Up @@ -2689,3 +2689,31 @@ reveal_type(x) # E: Revealed type is 'builtins.list[Any]'
reveal_type(y) # E: Revealed type is 'builtins.dict[Any, Any]'

[builtins fixtures/dict.pyi]

[case testInheritedAttributeNoStrictOptional]
# flags: --no-strict-optional
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I would also add a test case with --strict-optional as well (to avoid regressions).

class A:
x: str

class B(A):
x = None
x = ''
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Could you please also add a test where this causes an incompatible override error (an int)?

reveal_type(x) # E: Revealed type is 'builtins.str'

[case testIncompatibleInheritedAttributeNoStrictOptional]
# flags: --no-strict-optional
class A:
x: str

class B(A):
x = None
x = 2 # E: Incompatible types in assignment (expression has type "int", base class "A" defined the type as "str")

[case testInheritedAttributeStrictOptional]
# flags: --strict-optional
class A:
x: str

class B(A):
x = None # E: Incompatible types in assignment (expression has type "None", base class "A" defined the type as "str")
x = ''