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[ty] Add a subdiagnostic if invalid-return-type is emitted on a method with an empty body on a non-protocol subclass of a protocol class (#18243)

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Alex Waygood 2025-05-21 13:38:07 -04:00 • committed by GitHub
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6 changed files with 178 additions and 65 deletions
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16
crates/ty_python_semantic/resources/mdtest/function/return_type.md
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@ -397,3 +397,19 @@ async def i() -> typing.AsyncIterable:
async def j() -> str: # error: [invalid-return-type]
yield 42
```
## Diagnostics for `invalid-return-type` on non-protocol subclasses of protocol classes
<!-- snapshot-diagnostics -->
We emit a nice subdiagnostic in this situation explaining the probable error here:
```py
from typing_extensions import Protocol
class Abstract(Protocol):
def method(self) -> str: ...
class Concrete(Abstract):
def method(self) -> str: ... # error: [invalid-return-type]
```

48
crates/ty_python_semantic/resources/mdtest/snapshots/return_type.md_-_Function_return_type_-_Diagnostics_for_`inv…_(35563a74094b14d5).snap Normal file
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@ -0,0 +1,48 @@
---
source: crates/ty_test/src/lib.rs
expression: snapshot
---
---
mdtest name: return_type.md - Function return type - Diagnostics for `invalid-return-type` on non-protocol subclasses of protocol classes
mdtest path: crates/ty_python_semantic/resources/mdtest/function/return_type.md
---
# Python source files
## mdtest_snippet.py
```
1 | from typing_extensions import Protocol
2 |
3 | class Abstract(Protocol):
4 | def method(self) -> str: ...
5 |
6 | class Concrete(Abstract):
7 | def method(self) -> str: ... # error: [invalid-return-type]
```
# Diagnostics
```
error[invalid-return-type]: Function can implicitly return `None`, which is not assignable to return type `str`
--> src/mdtest_snippet.py:7:25
|
6 | class Concrete(Abstract):
7 | def method(self) -> str: ... # error: [invalid-return-type]
| ^^^
|
info: Only functions in stub files, methods on protocol classes, or methods with `@abstractmethod` are permitted to have empty bodies
info: Class `Concrete` has `typing.Protocol` in its MRO, but it is not a protocol class
info: Only classes that directly inherit from `typing.Protocol` or `typing_extensions.Protocol` are considered protocol classes
--> src/mdtest_snippet.py:6:7
|
4 | def method(self) -> str: ...
5 |
6 | class Concrete(Abstract):
| ^^^^^^^^^^^^^^^^^^ `Protocol` not present in `Concrete`'s immediate bases
7 | def method(self) -> str: ... # error: [invalid-return-type]
|
info: See https://typing.python.org/en/latest/spec/protocol.html#
info: rule `invalid-return-type` is enabled by default
```