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[ty] Strict validation of protocol members

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Alex Waygood 2025-04-30 22:56:46 +01:00
parent e658778ced
commit fdee512083
5 changed files with 225 additions and 10 deletions
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62
crates/ty_python_semantic/resources/mdtest/protocols.md
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@ -419,6 +419,8 @@ reveal_type(get_protocol_members(Baz2))
## Protocol members in statically known branches
<!-- snapshot-diagnostics -->
The list of protocol members does not include any members declared in branches that are statically
known to be unreachable:
@ -429,7 +431,7 @@ python-version = "3.9"
```py
import sys
from typing_extensions import Protocol, get_protocol_members
from typing_extensions import Protocol, get_protocol_members, reveal_type
class Foo(Protocol):
if sys.version_info >= (3, 10):
@ -438,7 +440,7 @@ class Foo(Protocol):
def c(self) -> None: ...
else:
d: int
e = 56
e = 56 # error: [invalid-protocol] "not declared as a protocol member"
def f(self) -> None: ...
reveal_type(get_protocol_members(Foo)) # revealed: frozenset[Literal["d", "e", "f"]]
@ -656,26 +658,70 @@ class LotsOfBindings(Protocol):
class Nested: ... # also weird, but we should also probably allow it
class NestedProtocol(Protocol): ... # same here...
e = 72 # TODO: this should error with `[invalid-protocol]` (`e` is not declared)
e = 72 # error: [invalid-protocol] "not declared as a protocol member"
f, g = (1, 2) # TODO: this should error with `[invalid-protocol]` (`f` and `g` are not declared)
# error: [invalid-protocol] "Cannot assign to variable `f` in body of protocol class `LotsOfBindings`"
# error: [invalid-protocol] "Cannot assign to variable `g` in body of protocol class `LotsOfBindings`"
f, g = (1, 2)
h: int = (i := 3) # TODO: this should error with `[invalid-protocol]` (`i` is not declared)
h: int = (i := 3) # error: [invalid-protocol] "not declared as a protocol member"
for j in range(42): # TODO: this should error with `[invalid-protocol]` (`j` is not declared)
for j in range(42): # error: [invalid-protocol] "not declared as a protocol member"
pass
with MyContext() as k: # TODO: this should error with `[invalid-protocol]` (`k` is not declared)
with MyContext() as k: # error: [invalid-protocol] "not declared as a protocol member"
pass
match object():
case l: # TODO: this should error with `[invalid-protocol]` (`l` is not declared)
case l: # error: [invalid-protocol] "not declared as a protocol member"
...
# revealed: frozenset[Literal["Nested", "NestedProtocol", "a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l"]]
reveal_type(get_protocol_members(LotsOfBindings))
```
A binding-without-declaration will not be reported if it occurs in a branch that we can statically
determine to be unreachable. The reason is that we don't consider it to be a protocol member at all
if all definitions for the variable are in unreachable blocks:
```py
import sys
class Protocol694(Protocol):
if sys.version_info > (3, 694):
x = 42 # no error!
```
If there are multiple bindings of the variable in the class body, however, and at least one of the
bindings occurs in a block of code that is understood to be (possibly) reachable, a diagnostic will
be reported. The diagnostic will be attached to the first binding that occurs in the class body,
even if that first definition occurs in an unreachable block:
```py
class Protocol695(Protocol):
if sys.version_info > (3, 695):
x = 42
else:
x = 42
# error: [invalid-protocol] "not declared as a protocol member"
x = 56
```
In order for the variable to be considered declared, the declaration of the variable must also take
place in a block of code that is understood to be (possibly) reachable:
```py
class Protocol696(Protocol):
if sys.version_info > (3, 696):
x: int
else:
x = 42 # error: [invalid-protocol] "not declared as a protocol member"
y: int
y = 56 # no error
```
Attribute members are allowed to have assignments in methods on the protocol class, just like
non-protocol classes. Unlike other classes, however, instance attributes that are not declared in
the class body are disallowed. This is mandated by [the spec][spec_protocol_members]: