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## Summary
Support `as` patterns in reachability analysis:
```py
from typing import assert_never
def f(subject: str | int):
match subject:
case int() as x:
pass
case str():
pass
case _:
assert_never(subject) # would previously emit an error
```
Note that we still don't support inferring correct types for the bound
name (`x`).
Closes https://github.com/astral-sh/ty/issues/928
## Test Plan
New Markdown tests
8.7 KiB
8.7 KiB
Exhaustiveness checking
[environment]
python-version = "3.11"
Checks on literals
from typing import Literal, assert_never
def if_else_exhaustive(x: Literal[0, 1, "a"]):
if x == 0:
pass
elif x == 1:
pass
elif x == "a":
pass
else:
no_diagnostic_here
assert_never(x)
def if_else_exhaustive_no_assertion(x: Literal[0, 1, "a"]) -> int:
if x == 0:
return 0
elif x == 1:
return 1
elif x == "a":
return 2
def if_else_non_exhaustive(x: Literal[0, 1, "a"]):
if x == 0:
pass
elif x == "a":
pass
else:
this_should_be_an_error # error: [unresolved-reference]
# this diagnostic is correct: the inferred type of `x` is `Literal[1]`
assert_never(x) # error: [type-assertion-failure]
def match_exhaustive(x: Literal[0, 1, "a"]):
match x:
case 0:
pass
case 1:
pass
case "a":
pass
case _:
no_diagnostic_here
assert_never(x)
def match_exhaustive_no_assertion(x: Literal[0, 1, "a"]) -> int:
match x:
case 0:
return 0
case 1:
return 1
case "a":
return 2
def match_non_exhaustive(x: Literal[0, 1, "a"]):
match x:
case 0:
pass
case "a":
pass
case _:
this_should_be_an_error # error: [unresolved-reference]
# this diagnostic is correct: the inferred type of `x` is `Literal[1]`
assert_never(x) # error: [type-assertion-failure]
Checks on enum literals
from enum import Enum
from typing import assert_never
class Color(Enum):
RED = 1
GREEN = 2
BLUE = 3
def if_else_exhaustive(x: Color):
if x == Color.RED:
pass
elif x == Color.GREEN:
pass
elif x == Color.BLUE:
pass
else:
no_diagnostic_here
assert_never(x)
def if_else_exhaustive_no_assertion(x: Color) -> int:
if x == Color.RED:
return 1
elif x == Color.GREEN:
return 2
elif x == Color.BLUE:
return 3
def if_else_non_exhaustive(x: Color):
if x == Color.RED:
pass
elif x == Color.BLUE:
pass
else:
this_should_be_an_error # error: [unresolved-reference]
# this diagnostic is correct: inferred type of `x` is `Literal[Color.GREEN]`
assert_never(x) # error: [type-assertion-failure]
def match_exhaustive(x: Color):
match x:
case Color.RED:
pass
case Color.GREEN:
pass
case Color.BLUE:
pass
case _:
no_diagnostic_here
assert_never(x)
def match_exhaustive_2(x: Color):
match x:
case Color.RED:
pass
case Color.GREEN | Color.BLUE:
pass
case _:
no_diagnostic_here
assert_never(x)
def match_exhaustive_no_assertion(x: Color) -> int:
match x:
case Color.RED:
return 1
case Color.GREEN:
return 2
case Color.BLUE:
return 3
def match_non_exhaustive(x: Color):
match x:
case Color.RED:
pass
case Color.BLUE:
pass
case _:
this_should_be_an_error # error: [unresolved-reference]
# this diagnostic is correct: inferred type of `x` is `Literal[Color.GREEN]`
assert_never(x) # error: [type-assertion-failure]
isinstance checks
from typing import assert_never
class A: ...
class B: ...
class C: ...
def if_else_exhaustive(x: A | B | C):
if isinstance(x, A):
pass
elif isinstance(x, B):
pass
elif isinstance(x, C):
pass
else:
no_diagnostic_here
assert_never(x)
def if_else_exhaustive_no_assertion(x: A | B | C) -> int:
if isinstance(x, A):
return 0
elif isinstance(x, B):
return 1
elif isinstance(x, C):
return 2
def if_else_non_exhaustive(x: A | B | C):
if isinstance(x, A):
pass
elif isinstance(x, C):
pass
else:
this_should_be_an_error # error: [unresolved-reference]
# this diagnostic is correct: the inferred type of `x` is `B & ~A & ~C`
assert_never(x) # error: [type-assertion-failure]
def match_exhaustive(x: A | B | C):
match x:
case A():
pass
case B():
pass
case C():
pass
case _:
no_diagnostic_here
assert_never(x)
def match_exhaustive_no_assertion(x: A | B | C) -> int:
match x:
case A():
return 0
case B():
return 1
case C():
return 2
def match_non_exhaustive(x: A | B | C):
match x:
case A():
pass
case C():
pass
case _:
this_should_be_an_error # error: [unresolved-reference]
# this diagnostic is correct: the inferred type of `x` is `B & ~A & ~C`
assert_never(x) # error: [type-assertion-failure]
isinstance checks with generics
[environment]
python-version = "3.12"
from typing import assert_never
class A[T]: ...
class ASub[T](A[T]): ...
class B[T]: ...
class C[T]: ...
class D: ...
class E: ...
class F: ...
def if_else_exhaustive(x: A[D] | B[E] | C[F]):
if isinstance(x, A):
pass
elif isinstance(x, B):
pass
elif isinstance(x, C):
pass
else:
# TODO: both of these are false positives (https://github.com/astral-sh/ty/issues/456)
no_diagnostic_here # error: [unresolved-reference]
assert_never(x) # error: [type-assertion-failure]
# TODO: false-positive diagnostic (https://github.com/astral-sh/ty/issues/456)
def if_else_exhaustive_no_assertion(x: A[D] | B[E] | C[F]) -> int: # error: [invalid-return-type]
if isinstance(x, A):
return 0
elif isinstance(x, B):
return 1
elif isinstance(x, C):
return 2
def if_else_non_exhaustive(x: A[D] | B[E] | C[F]):
if isinstance(x, A):
pass
elif isinstance(x, C):
pass
else:
this_should_be_an_error # error: [unresolved-reference]
# this diagnostic is correct: the inferred type of `x` is `B[E] & ~A[D] & ~C[F]`
assert_never(x) # error: [type-assertion-failure]
def match_exhaustive(x: A[D] | B[E] | C[F]):
match x:
case A():
pass
case B():
pass
case C():
pass
case _:
# TODO: both of these are false positives (https://github.com/astral-sh/ty/issues/456)
no_diagnostic_here # error: [unresolved-reference]
assert_never(x) # error: [type-assertion-failure]
# TODO: false-positive diagnostic (https://github.com/astral-sh/ty/issues/456)
def match_exhaustive_no_assertion(x: A[D] | B[E] | C[F]) -> int: # error: [invalid-return-type]
match x:
case A():
return 0
case B():
return 1
case C():
return 2
def match_non_exhaustive(x: A[D] | B[E] | C[F]):
match x:
case A():
pass
case C():
pass
case _:
this_should_be_an_error # error: [unresolved-reference]
# this diagnostic is correct: the inferred type of `x` is `B[E] & ~A[D] & ~C[F]`
assert_never(x) # error: [type-assertion-failure]
# This function might seem a bit silly, but it's a pattern that exists in real-world code!
# see https://github.com/bokeh/bokeh/blob/adef0157284696ce86961b2089c75fddda53c15c/src/bokeh/core/property/container.py#L130-L140
def no_invalid_return_diagnostic_here_either[T](x: A[T]) -> ASub[T]:
if isinstance(x, A):
if isinstance(x, ASub):
return x
else:
return ASub()
else:
# We *would* emit a diagnostic here complaining that it's an invalid `return` statement
# ...except that we (correctly) infer that this branch is unreachable, so the complaint
# is null and void (and therefore we don't emit a diagnostic)
return x
More match pattern types
as patterns
from typing import assert_never
def as_pattern_exhaustive(subject: int | str):
match subject:
case int() as x:
pass
case str() as y:
pass
case _:
no_diagnostic_here
assert_never(subject)
def as_pattern_non_exhaustive(subject: int | str):
match subject:
case int() as x:
pass
case _:
this_should_be_an_error # error: [unresolved-reference]
# this diagnostic is correct: the inferred type of `subject` is `str`
assert_never(subject) # error: [type-assertion-failure]