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Fix typeguards crash when assigning guarded value in if statement #10671

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Fix typeguards crash when assigning guarded value in if statement #10671

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3f068f5
Do not annotate variables as type guards
A5rocks Jun 19, 2021
707cfdf
Remove unneeded import
A5rocks Jun 19, 2021
12dbc2a
Tests failed, trying a different approach
A5rocks Jun 19, 2021
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2 changes: 1 addition & 1 deletion mypy/join.py
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Original file line number Diff line number Diff line change
Expand Up @@ -433,7 +433,7 @@ def visit_type_alias_type(self, t: TypeAliasType) -> ProperType:
assert False, "This should be never called, got {}".format(t)

def visit_type_guard_type(self, t: TypeGuardType) -> ProperType:
assert False, "This should be never called, got {}".format(t)
return t.type_guard.accept(self)
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I don't think this is right, since for join(T, TypeGuard[U]) it will end up with join(T, U), which is approximately Union[T, U] in practice. Computing join(T, bool) may make more sense.

I'm not sure what practical effect this has though. It's at least clear that we'll have to make sure we handle TypeGuard correctly in more places in the codebase.

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@A5rocks A5rocks Jun 19, 2021 •
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The thing is, it's (in the example crash code) saying a is TypeGuard[B] -- when it's actually B (?). (and then it is joining the type with the type of a in the outer scope). However, when I changed that (3f068f5) some of the test cases started erroring... in specific, some of the narrowing ones:

_____________________________________________________________ testTypeGuardNonOverlapping _____________________________________________________________
[gw6] linux -- Python 3.8.2 /home/a5/.virtualenvs/tmp-7d419bcf0dbd427/bin/python
data: /home/a5/oss/mypy/test-data/unit/check-typeguard.test:78:
/home/a5/oss/mypy/mypy/test/testcheck.py:137: in run_case
    self.run_case_once(testcase)
/home/a5/oss/mypy/mypy/test/testcheck.py:236: in run_case_once
    assert_string_arrays_equal(output, a, msg.format(testcase.file, testcase.line))
E   AssertionError: Unexpected type checker output (/home/a5/oss/mypy/test-data/unit/check-typeguard.test, line 78)
---------------------------------------------------------------- Captured stderr call -----------------------------------------------------------------
Expected:
  main:6: note: Revealed type is "builtins.list[builtins.str]" (diff)
Actual:
  main:6: note: Revealed type is "None"         (diff)

Alignment of first line difference:
  E: ...te: Revealed type is "builtins.list[builtins.str]"
  A: ...te: Revealed type is "None"
                              ^
______________________________________________________________ testTypeGuardNonzeroFloat ______________________________________________________________
[gw6] linux -- Python 3.8.2 /home/a5/.virtualenvs/tmp-7d419bcf0dbd427/bin/python
data: /home/a5/oss/mypy/test-data/unit/check-typeguard.test:105:
/home/a5/oss/mypy/mypy/test/testcheck.py:137: in run_case
    self.run_case_once(testcase)
/home/a5/oss/mypy/mypy/test/testcheck.py:236: in run_case_once
    assert_string_arrays_equal(output, a, msg.format(testcase.file, testcase.line))
E   AssertionError: Unexpected type checker output (/home/a5/oss/mypy/test-data/unit/check-typeguard.test, line 105)
---------------------------------------------------------------- Captured stderr call -----------------------------------------------------------------
Expected:
  main:5: note: Revealed type is "builtins.float" (diff)
Actual:
  main:5: note: Revealed type is "builtins.int" (diff)

Alignment of first line difference:
  E: ...ed type is "builtins.float"
  A: ...ed type is "builtins.int"
                             ^
___________________________________________________________ testTypeGuardNarrowToTypedDict ____________________________________________________________
[gw6] linux -- Python 3.8.2 /home/a5/.virtualenvs/tmp-7d419bcf0dbd427/bin/python
data: /home/a5/oss/mypy/test-data/unit/check-typeguard.test:155:
/home/a5/oss/mypy/mypy/test/testcheck.py:137: in run_case
    self.run_case_once(testcase)
/home/a5/oss/mypy/mypy/test/testcheck.py:236: in run_case_once
    assert_string_arrays_equal(output, a, msg.format(testcase.file, testcase.line))
E   AssertionError: Unexpected type checker output (/home/a5/oss/mypy/test-data/unit/check-typeguard.test, line 155)
---------------------------------------------------------------- Captured stderr call -----------------------------------------------------------------
Expected:
  main:10: note: Revealed type is "TypedDict('__main__.User', {'name': builtins.str, 'id': builtins.int})" (diff)
Actual:
  main:10: note: Revealed type is "None"        (diff)

Alignment of first line difference:
  E: ...ote: Revealed type is "TypedDict('__main__.User', {'name': builtins.s...
  A: ...ote: Revealed type is "None"...
                               ^

Because of that, I kind of assumed that TypeGuard[T] is just T -- I guess that isn't the case though? If so, then this might be more annoying to fix...


def join(self, s: Type, t: Type) -> ProperType:
return join_types(s, t)
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14 changes: 14 additions & 0 deletions test-data/unit/check-typeguard.test
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Original file line number Diff line number Diff line change
Expand Up @@ -315,3 +315,17 @@ def coverage(obj: Any) -> bool:
return True
return False
[builtins fixtures/classmethod.pyi]

[case testTypeGuardAssignment]
from typing_extensions import TypeGuard

class A: pass
class B(A): pass

def guard(a: A) -> TypeGuard[B]:
pass

a = A()
if not guard(a):
a = A()
[builtins fixtures/tuple.pyi]