[pyupgrade] Ignore Optional[None] in UP045/UP007

Author: robsdedude

crates/ruff_linter/resources/test/fixtures/pyupgrade/UP045.py

@@ -42,3 +42,8 @@ class ServiceRefOrValue:
 # Regression test for: https://github.com/astral-sh/ruff/issues/7201
 class ServiceRefOrValue:
     service_specification: Optional[str]is not True = None
+
+
+# Test for: https://github.com/astral-sh/ruff/issues/18508
+# Optional[None] should be ignored
+foo: Optional[None] = None

crates/ruff_linter/src/rules/pyupgrade/rules/use_pep604_annotation.rs

@@ -74,6 +74,8 @@ impl Violation for NonPEP604AnnotationUnion {
 /// ## What it does
 /// Check for `typing.Optional` annotations that can be rewritten based on [PEP 604] syntax.
 ///
+/// `Optional[None]` is exempt from this rule, as the intention is unclear.
+///
 /// ## Why is this bad?
 /// [PEP 604] introduced a new syntax for union type annotations based on the
 /// `|` operator. This syntax is more concise and readable than the previous
@@ -100,8 +102,8 @@ impl Violation for NonPEP604AnnotationUnion {
 /// ```
 ///
 /// ## Fix safety
-/// This rule's fix is marked as unsafe, as it may lead to runtime errors when
-/// alongside libraries that rely on runtime type annotations, like Pydantic,
+/// This rule's fix is marked as unsafe, as it may lead to runtime errors
+/// using libraries that rely on runtime type annotations, like Pydantic,
 /// on Python versions prior to Python 3.10. It may also lead to runtime errors
 /// in unusual and likely incorrect type annotations where the type does not
 /// support the `|` operator.
@@ -140,6 +142,11 @@ pub(crate) fn non_pep604_annotation(
         && !checker.semantic().in_complex_string_type_definition()
         && is_allowed_value(slice);
 
+    if matches!(operator, Pep604Operator::Optional) && matches!(slice, Expr::NoneLiteral(_)) {
+        // `Optional[None]` is exempt from this rule.
+        return;
+    }
+
     let applicability = if checker.target_version() >= PythonVersion::PY310 {
         Applicability::Safe
     } else {

crates/ruff_linter/src/rules/pyupgrade/snapshots/ruff_linter__rules__pyupgrade__tests__UP045.py.snap

@@ -1,6 +1,5 @@
 ---
 source: crates/ruff_linter/src/rules/pyupgrade/mod.rs
-snapshot_kind: text
 ---
 UP045.py:5:10: UP007 [*] Use `X | Y` for type annotations
   |
@@ -149,3 +148,6 @@ UP045.py:44:28: UP007 [*] Use `X | Y` for type annotations
 43 43 | class ServiceRefOrValue:
 44    |-    service_specification: Optional[str]is not True = None
    44 |+    service_specification: str | None is not True = None
+45 45 | 
+46 46 | 
+47 47 | # Test for: https://github.com/astral-sh/ruff/issues/18508