add implicitly concatenated annotation tests

crates/ruff_linter/resources/test/fixtures/pyupgrade/UP045_py39.py

@@ -0,0 +1,35 @@
+"""
+Regression test for https://github.com/astral-sh/ruff/issues/20096
+"""
+
+from __future__ import annotations
+
+from typing import Optional, cast, TypeAlias
+
+
+x: Optional[str]             # UP045
+x: "Optional[str]"           # UP045
+cast("Optional[str]", None)  # UP045
+cast(Optional[str], None)    # okay, str | None is a runtime error
+x: TypeAlias = "Optional[str]"  # UP045
+x: TypeAlias = Optional[str]  # okay
+
+# complex (implicitly concatenated) annotations
+x: (
+    "Optional"
+    "["
+    "str"
+    "]"
+)
+cast((
+    "Optional"
+    "["
+    "str"
+    "]"
+), None)
+x: TypeAlias = (
+    "Optional"
+    "["
+    "str"
+    "]"
+)

crates/ruff_linter/src/checkers/ast/analyze/expression.rs

@@ -54,7 +54,8 @@ pub(crate) fn expression(expr: &Expr, checker: &Checker) {
                             || checker.target_version() >= PythonVersion::PY310
                             || (checker.target_version() >= PythonVersion::PY37
                                 && checker.semantic.future_annotations_or_stub()
-                                && checker.semantic.in_annotation()
+                                && (checker.semantic.in_annotation()
+                                    || checker.semantic.in_string_type_definition())
                                 && !checker.settings().pyupgrade.keep_runtime_typing)
                         {
                             pyupgrade::rules::non_pep604_annotation(checker, expr, slice, operator);

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

@@ -452,4 +452,17 @@ mod tests {
         assert_diagnostics!(snapshot, diagnostics);
         Ok(())
     }
+
+    #[test]
+    fn up045_future_annotations_py39() -> Result<()> {
+        let diagnostics = test_path(
+            Path::new("pyupgrade/UP045_py39.py"),
+            &settings::LinterSettings {
+                unresolved_target_version: PythonVersion::PY39.into(),
+                ..settings::LinterSettings::for_rule(Rule::NonPEP604AnnotationOptional)
+            },
+        )?;
+        assert_diagnostics!(diagnostics);
+        Ok(())
+    }
 }

crates/ruff_linter/src/rules/pyupgrade/snapshots/ruff_linter__rules__pyupgrade__tests__up045_future_annotations_py39.snap

@@ -0,0 +1,82 @@
+---
+source: crates/ruff_linter/src/rules/pyupgrade/mod.rs
+---
+UP045 [*] Use `X | None` for type annotations
+  --> UP045_py39.py:10:4
+   |
+10 | x: Optional[str]             # UP045
+   |    ^^^^^^^^^^^^^
+11 | x: "Optional[str]"           # UP045
+12 | cast("Optional[str]", None)  # UP045
+   |
+help: Convert to `X | None`
+7  | from typing import Optional, cast, TypeAlias
+8  | 
+9  | 
+   - x: Optional[str]             # UP045
+10 + x: str | None             # UP045
+11 | x: "Optional[str]"           # UP045
+12 | cast("Optional[str]", None)  # UP045
+13 | cast(Optional[str], None)    # okay, str | None is a runtime error
+note: This is an unsafe fix and may change runtime behavior
+
+UP045 [*] Use `X | None` for type annotations
+  --> UP045_py39.py:11:5
+   |
+10 | x: Optional[str]             # UP045
+11 | x: "Optional[str]"           # UP045
+   |     ^^^^^^^^^^^^^
+12 | cast("Optional[str]", None)  # UP045
+13 | cast(Optional[str], None)    # okay, str | None is a runtime error
+   |
+help: Convert to `X | None`
+8  | 
+9  | 
+10 | x: Optional[str]             # UP045
+   - x: "Optional[str]"           # UP045
+11 + x: "str | None"           # UP045
+12 | cast("Optional[str]", None)  # UP045
+13 | cast(Optional[str], None)    # okay, str | None is a runtime error
+14 | x: TypeAlias = "Optional[str]"  # UP045
+note: This is an unsafe fix and may change runtime behavior
+
+UP045 [*] Use `X | None` for type annotations
+  --> UP045_py39.py:12:7
+   |
+10 | x: Optional[str]             # UP045
+11 | x: "Optional[str]"           # UP045
+12 | cast("Optional[str]", None)  # UP045
+   |       ^^^^^^^^^^^^^
+13 | cast(Optional[str], None)    # okay, str | None is a runtime error
+14 | x: TypeAlias = "Optional[str]"  # UP045
+   |
+help: Convert to `X | None`
+9  | 
+10 | x: Optional[str]             # UP045
+11 | x: "Optional[str]"           # UP045
+   - cast("Optional[str]", None)  # UP045
+12 + cast("str | None", None)  # UP045
+13 | cast(Optional[str], None)    # okay, str | None is a runtime error
+14 | x: TypeAlias = "Optional[str]"  # UP045
+15 | x: TypeAlias = Optional[str]  # okay
+note: This is an unsafe fix and may change runtime behavior
+
+UP045 [*] Use `X | None` for type annotations
+  --> UP045_py39.py:14:17
+   |
+12 | cast("Optional[str]", None)  # UP045
+13 | cast(Optional[str], None)    # okay, str | None is a runtime error
+14 | x: TypeAlias = "Optional[str]"  # UP045
+   |                 ^^^^^^^^^^^^^
+15 | x: TypeAlias = Optional[str]  # okay
+   |
+help: Convert to `X | None`
+11 | x: "Optional[str]"           # UP045
+12 | cast("Optional[str]", None)  # UP045
+13 | cast(Optional[str], None)    # okay, str | None is a runtime error
+   - x: TypeAlias = "Optional[str]"  # UP045
+14 + x: TypeAlias = "str | None"  # UP045
+15 | x: TypeAlias = Optional[str]  # okay
+16 | 
+17 | # complex (implicitly concatenated) annotations
+note: This is an unsafe fix and may change runtime behavior