Avoid applying `PYI055` to runtime-evaluated annotations (#6457)

## Summary

The use of `|` as a union operator is not always safe, if a type
annotation is evaluated in a runtime context. For example, this code
errors at runtime:

```python
import httpretty
import requests_mock

item: type[requests_mock.Mocker | httpretty] = requests_mock.Mocker
```

However, it's fine in a `.pyi` file, with `__future__` annotations`, or
if the annotation is in a non-evaluated context, like:

```python
def func():
    item: type[requests_mock.Mocker | httpretty] = requests_mock.Mocker
```

This PR modifies the rule to avoid enforcing in those invalid,
runtime-evaluated contexts.

Closes https://github.com/astral-sh/ruff/issues/6455.

crates/ruff/resources/test/fixtures/flake8_pyi/PYI055.py

@@ -1,7 +1,6 @@
 import builtins
 from typing import Union
 
-
 w: builtins.type[int] | builtins.type[str] | builtins.type[complex]
 x: type[int] | type[str] | type[float]
 y: builtins.type[int] | type[str] | builtins.type[complex]
@@ -9,7 +8,9 @@ z: Union[type[float], type[complex]]
 z: Union[type[float, int], type[complex]]
 
 
-def func(arg: type[int] | str | type[float]) -> None: ...
+def func(arg: type[int] | str | type[float]) -> None:
+    ...
+
 
 # OK
 x: type[int, str, float]
@@ -17,4 +18,14 @@ y: builtins.type[int, str, complex]
 z: Union[float, complex]
 
 
-def func(arg: type[int, float] | str) -> None: ...
+def func(arg: type[int, float] | str) -> None:
+    ...
+
+
+# OK
+item: type[requests_mock.Mocker] | type[httpretty] = requests_mock.Mocker
+
+
+def func():
+    # PYI055
+    item: type[requests_mock.Mocker] | type[httpretty] = requests_mock.Mocker

crates/ruff/resources/test/fixtures/flake8_pyi/PYI055.pyi

@@ -1,14 +1,12 @@
 import builtins
 from typing import Union
 
-
 w: builtins.type[int] | builtins.type[str] | builtins.type[complex]
 x: type[int] | type[str] | type[float]
 y: builtins.type[int] | type[str] | builtins.type[complex]
 z: Union[type[float], type[complex]]
 z: Union[type[float, int], type[complex]]
 
-
 def func(arg: type[int] | str | type[float]) -> None: ...
 
 # OK
@@ -16,5 +14,11 @@ x: type[int, str, float]
 y: builtins.type[int, str, complex]
 z: Union[float, complex]
 
-
 def func(arg: type[int, float] | str) -> None: ...
+
+# OK
+item: type[requests_mock.Mocker] | type[httpretty] = requests_mock.Mocker
+
+def func():
+    # PYI055
+    item: type[requests_mock.Mocker] | type[httpretty] = requests_mock.Mocker

crates/ruff/src/rules/flake8_pyi/rules/unnecessary_type_union.rs

@@ -43,6 +43,11 @@ impl Violation for UnnecessaryTypeUnion {
 
 /// PYI055
 pub(crate) fn unnecessary_type_union<'a>(checker: &mut Checker, union: &'a Expr) {
+    // The `|` operator isn't always safe to allow to runtime-evaluated annotations.
+    if checker.semantic().execution_context().is_runtime() {
+        return;
+    }
+
     let mut type_exprs = Vec::new();
 
     // Check if `union` is a PEP604 union (e.g. `float | int`) or a `typing.Union[float, int]`

crates/ruff/src/rules/flake8_pyi/snapshots/ruff__rules__flake8_pyi__tests__PYI055_PYI055.py.snap

@@ -1,56 +1,12 @@
 ---
 source: crates/ruff/src/rules/flake8_pyi/mod.rs
 ---
-PYI055.py:5:4: PYI055 Multiple `type` members in a union. Combine them into one, e.g., `type[int | str | complex]`.
+PYI055.py:31:11: PYI055 Multiple `type` members in a union. Combine them into one, e.g., `type[requests_mock.Mocker | httpretty]`.
-  |
-5 | w: builtins.type[int] | builtins.type[str] | builtins.type[complex]
-  |    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ PYI055
-6 | x: type[int] | type[str] | type[float]
-7 | y: builtins.type[int] | type[str] | builtins.type[complex]
-  |
-
-PYI055.py:6:4: PYI055 Multiple `type` members in a union. Combine them into one, e.g., `type[int | str | float]`.
-  |
-5 | w: builtins.type[int] | builtins.type[str] | builtins.type[complex]
-6 | x: type[int] | type[str] | type[float]
-  |    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ PYI055
-7 | y: builtins.type[int] | type[str] | builtins.type[complex]
-8 | z: Union[type[float], type[complex]]
-  |
-
-PYI055.py:7:4: PYI055 Multiple `type` members in a union. Combine them into one, e.g., `type[int | str | complex]`.
-  |
-5 | w: builtins.type[int] | builtins.type[str] | builtins.type[complex]
-6 | x: type[int] | type[str] | type[float]
-7 | y: builtins.type[int] | type[str] | builtins.type[complex]
-  |    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ PYI055
-8 | z: Union[type[float], type[complex]]
-9 | z: Union[type[float, int], type[complex]]
-  |
-
-PYI055.py:8:4: PYI055 Multiple `type` members in a union. Combine them into one, e.g., `type[Union[float, complex]]`.
-  |
-6 | x: type[int] | type[str] | type[float]
-7 | y: builtins.type[int] | type[str] | builtins.type[complex]
-8 | z: Union[type[float], type[complex]]
-  |    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ PYI055
-9 | z: Union[type[float, int], type[complex]]
-  |
-
-PYI055.py:9:4: PYI055 Multiple `type` members in a union. Combine them into one, e.g., `type[Union[float, int, complex]]`.
-  |
-7 | y: builtins.type[int] | type[str] | builtins.type[complex]
-8 | z: Union[type[float], type[complex]]
-9 | z: Union[type[float, int], type[complex]]
-  |    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ PYI055
-  |
-
-PYI055.py:12:15: PYI055 Multiple `type` members in a union. Combine them into one, e.g., `type[int | float]`.
    |
-12 | def func(arg: type[int] | str | type[float]) -> None: ...
+29 | def func():
-   |               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ PYI055
+30 |     # PYI055
-13 | 
+31 |     item: type[requests_mock.Mocker] | type[httpretty] = requests_mock.Mocker
-14 | # OK
+   |           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ PYI055
    |
 
 

crates/ruff/src/rules/flake8_pyi/snapshots/ruff__rules__flake8_pyi__tests__PYI055_PYI055.pyi.snap

@@ -1,56 +1,79 @@
 ---
 source: crates/ruff/src/rules/flake8_pyi/mod.rs
 ---
-PYI055.pyi:5:4: PYI055 Multiple `type` members in a union. Combine them into one, e.g., `type[int | str | complex]`.
+PYI055.pyi:4:4: PYI055 Multiple `type` members in a union. Combine them into one, e.g., `type[int | str | complex]`.
   |
-5 | w: builtins.type[int] | builtins.type[str] | builtins.type[complex]
+2 | from typing import Union
+3 | 
+4 | w: builtins.type[int] | builtins.type[str] | builtins.type[complex]
   |    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ PYI055
-6 | x: type[int] | type[str] | type[float]
+5 | x: type[int] | type[str] | type[float]
-7 | y: builtins.type[int] | type[str] | builtins.type[complex]
+6 | y: builtins.type[int] | type[str] | builtins.type[complex]
   |
 
-PYI055.pyi:6:4: PYI055 Multiple `type` members in a union. Combine them into one, e.g., `type[int | str | float]`.
+PYI055.pyi:5:4: PYI055 Multiple `type` members in a union. Combine them into one, e.g., `type[int | str | float]`.
   |
-5 | w: builtins.type[int] | builtins.type[str] | builtins.type[complex]
+4 | w: builtins.type[int] | builtins.type[str] | builtins.type[complex]
-6 | x: type[int] | type[str] | type[float]
+5 | x: type[int] | type[str] | type[float]
   |    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ PYI055
-7 | y: builtins.type[int] | type[str] | builtins.type[complex]
+6 | y: builtins.type[int] | type[str] | builtins.type[complex]
-8 | z: Union[type[float], type[complex]]
+7 | z: Union[type[float], type[complex]]
   |
 
-PYI055.pyi:7:4: PYI055 Multiple `type` members in a union. Combine them into one, e.g., `type[int | str | complex]`.
+PYI055.pyi:6:4: PYI055 Multiple `type` members in a union. Combine them into one, e.g., `type[int | str | complex]`.
   |
-5 | w: builtins.type[int] | builtins.type[str] | builtins.type[complex]
+4 | w: builtins.type[int] | builtins.type[str] | builtins.type[complex]
-6 | x: type[int] | type[str] | type[float]
+5 | x: type[int] | type[str] | type[float]
-7 | y: builtins.type[int] | type[str] | builtins.type[complex]
+6 | y: builtins.type[int] | type[str] | builtins.type[complex]
   |    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ PYI055
-8 | z: Union[type[float], type[complex]]
+7 | z: Union[type[float], type[complex]]
-9 | z: Union[type[float, int], type[complex]]
+8 | z: Union[type[float, int], type[complex]]
   |
 
-PYI055.pyi:8:4: PYI055 Multiple `type` members in a union. Combine them into one, e.g., `type[Union[float, complex]]`.
+PYI055.pyi:7:4: PYI055 Multiple `type` members in a union. Combine them into one, e.g., `type[Union[float, complex]]`.
   |
-6 | x: type[int] | type[str] | type[float]
+5 | x: type[int] | type[str] | type[float]
-7 | y: builtins.type[int] | type[str] | builtins.type[complex]
+6 | y: builtins.type[int] | type[str] | builtins.type[complex]
-8 | z: Union[type[float], type[complex]]
+7 | z: Union[type[float], type[complex]]
   |    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ PYI055
-9 | z: Union[type[float, int], type[complex]]
+8 | z: Union[type[float, int], type[complex]]
   |
 
-PYI055.pyi:9:4: PYI055 Multiple `type` members in a union. Combine them into one, e.g., `type[Union[float, int, complex]]`.
+PYI055.pyi:8:4: PYI055 Multiple `type` members in a union. Combine them into one, e.g., `type[Union[float, int, complex]]`.
-  |
-7 | y: builtins.type[int] | type[str] | builtins.type[complex]
-8 | z: Union[type[float], type[complex]]
-9 | z: Union[type[float, int], type[complex]]
-  |    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ PYI055
-  |
-
-PYI055.pyi:12:15: PYI055 Multiple `type` members in a union. Combine them into one, e.g., `type[int | float]`.
    |
-12 | def func(arg: type[int] | str | type[float]) -> None: ...
+ 6 | y: builtins.type[int] | type[str] | builtins.type[complex]
+ 7 | z: Union[type[float], type[complex]]
+ 8 | z: Union[type[float, int], type[complex]]
+   |    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ PYI055
+ 9 | 
+10 | def func(arg: type[int] | str | type[float]) -> None: ...
+   |
+
+PYI055.pyi:10:15: PYI055 Multiple `type` members in a union. Combine them into one, e.g., `type[int | float]`.
+   |
+ 8 | z: Union[type[float, int], type[complex]]
+ 9 | 
+10 | def func(arg: type[int] | str | type[float]) -> None: ...
    |               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ PYI055
-13 | 
+11 | 
-14 | # OK
+12 | # OK
+   |
+
+PYI055.pyi:20:7: PYI055 Multiple `type` members in a union. Combine them into one, e.g., `type[requests_mock.Mocker | httpretty]`.
+   |
+19 | # OK
+20 | item: type[requests_mock.Mocker] | type[httpretty] = requests_mock.Mocker
+   |       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ PYI055
+21 | 
+22 | def func():
+   |
+
+PYI055.pyi:24:11: PYI055 Multiple `type` members in a union. Combine them into one, e.g., `type[requests_mock.Mocker | httpretty]`.
+   |
+22 | def func():
+23 |     # PYI055
+24 |     item: type[requests_mock.Mocker] | type[httpretty] = requests_mock.Mocker
+   |           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ PYI055
    |