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Fix type inference regression with partial types #8091

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Merged
merged 4 commits into from
Dec 6, 2019
Merged

Fix type inference regression with partial types #8091

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268092f
Fix type inference regression
JukkaL Dec 5, 2019
de6902f
Better fix
JukkaL Dec 5, 2019
cf19dfa
Fix special case
JukkaL Dec 6, 2019
a8441e0
Revert unrelated change
JukkaL Dec 6, 2019
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12 changes: 10 additions & 2 deletions mypy/checker.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2174,7 +2174,10 @@ def try_infer_partial_generic_type_from_assignment(self,
rvalue_type = get_proper_type(rvalue_type)
if isinstance(rvalue_type, Instance):
if rvalue_type.type == typ.type:
var.type = rvalue_type
if is_valid_inferred_type(rvalue_type):
var.type = rvalue_type
else:
var.type = self.inference_error_fallback_type(rvalue_type)
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What if one just assigns the variable twice (without reading it), would it silence the error on first assignment? Not that it is too bad, but still may be surprising.

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Yeah, a good catch! This behavior is inconsistent. I'll try to fix it.

del partial_types[var]
elif isinstance(rvalue_type, AnyType):
var.type = fill_typevars_with_any(typ.type)
Expand Down Expand Up @@ -2785,6 +2788,7 @@ def infer_variable_type(self, name: Var, lvalue: Lvalue,
init_type = get_proper_type(init_type)
if isinstance(init_type, DeletedType):
self.msg.deleted_as_rvalue(init_type, context)
name.type = AnyType(TypeOfAny.from_error)
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Is there a test for this?

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No, and this is kind of an unrelated thing that I encountered when trying a different fix. I might take this out of this PR.

elif not is_valid_inferred_type(init_type) and not self.no_partial_types:
# We cannot use the type of the initialization expression for full type
# inference (it's not specific enough), but we might be able to give
Expand Down Expand Up @@ -2855,10 +2859,14 @@ def set_inference_error_fallback_type(self, var: Var, lvalue: Lvalue, type: Type

We implement this here by giving x a valid type (replacing inferred <nothing> with Any).
"""
fallback = self.inference_error_fallback_type(type)
self.set_inferred_type(var, lvalue, fallback)

def inference_error_fallback_type(self, type: Type) -> Type:
fallback = type.accept(SetNothingToAny())
# Type variables may leak from inference, see https://github.com/python/mypy/issues/5738,
# we therefore need to erase them.
self.set_inferred_type(var, lvalue, erase_typevars(fallback))
return erase_typevars(fallback)

def check_simple_assignment(self, lvalue_type: Optional[Type], rvalue: Expression,
context: Context,
Expand Down
16 changes: 16 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 @@ -1585,6 +1585,22 @@ oo.update(d)
reveal_type(oo) # N: Revealed type is 'collections.OrderedDict[builtins.int*, builtins.str*]'
[builtins fixtures/dict.pyi]

[case testEmptyCollectionAssignedToVariableTwiceIncremental]
x = [] # E: Need type annotation for 'x' (hint: "x: List[<type>] = ...")
y = x
x = []
reveal_type(x) # N: Revealed type is 'builtins.list[Any]'
d = {} # E: Need type annotation for 'd' (hint: "d: Dict[<type>, <type>] = ...")
z = d
d = {}
reveal_type(d) # N: Revealed type is 'builtins.dict[Any, Any]'
[builtins fixtures/dict.pyi]
[out2]
main:1: error: Need type annotation for 'x' (hint: "x: List[<type>] = ...")
main:4: note: Revealed type is 'builtins.list[Any]'
main:5: error: Need type annotation for 'd' (hint: "d: Dict[<type>, <type>] = ...")
main:8: note: Revealed type is 'builtins.dict[Any, Any]'

[case testInferAttributeInitializedToEmptyAndAssigned]
class C:
def __init__(self) -> None:
Expand Down