Update non-pep695-type-alias to require --unsafe-fixes outside of…

… stub files (#7836)

Closes #6434

crates/ruff_linter/resources/test/fixtures/pyupgrade/UP040.pyi

@@ -0,0 +1,7 @@
+import typing
+from typing import TypeAlias
+
+# UP040
+# Fixes in type stub files should be safe to apply unlike in regular code where runtime behavior could change
+x: typing.TypeAlias = int
+x: TypeAlias = int

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

@@ -83,6 +83,7 @@ mod tests {
     #[test_case(Rule::YieldInForLoop, Path::new("UP028_0.py"))]
     #[test_case(Rule::YieldInForLoop, Path::new("UP028_1.py"))]
     #[test_case(Rule::NonPEP695TypeAlias, Path::new("UP040.py"))]
+    #[test_case(Rule::NonPEP695TypeAlias, Path::new("UP040.pyi"))]
     fn rules(rule_code: Rule, path: &Path) -> Result<()> {
         let snapshot = path.to_string_lossy().to_string();
         let diagnostics = test_path(

crates/ruff_linter/src/rules/pyupgrade/rules/use_pep695_type_alias.rs

@@ -132,15 +132,25 @@ pub(crate) fn non_pep695_type_alias(checker: &mut Checker, stmt: &StmtAnnAssign)
             })
         };
 
-        diagnostic.set_fix(Fix::always_applies(Edit::range_replacement(
+        let edit = Edit::range_replacement(
             checker.generator().stmt(&Stmt::from(StmtTypeAlias {
                 range: TextRange::default(),
                 name: target.clone(),
                 type_params,
                 value: value.clone(),
             })),
             stmt.range(),
-        )));
+        );
+
+        // The fix is only safe in a type stub because new-style aliases have different runtime  behavior
+        // See https://github.com/astral-sh/ruff/issues/6434
+        let fix = if checker.source_type.is_stub() {
+            Fix::always_applies(edit)
+        } else {
+            Fix::sometimes_applies(edit)
+        };
+
+        diagnostic.set_fix(fix);
     }
     checker.diagnostics.push(diagnostic);
 }

crates/ruff_linter/src/rules/pyupgrade/snapshots/ruff_linter__rules__pyupgrade__tests__UP040.py.snap

@@ -10,7 +10,7 @@ UP040.py:5:1: UP040 [*] Type alias `x` uses `TypeAlias` annotation instead of th
   |
   = help: Use the `type` keyword
 
-ℹ Fix
+ℹ Suggested fix
 2 2 | from typing import TypeAlias
 3 3 | 
 4 4 | # UP040
@@ -31,7 +31,7 @@ UP040.py:6:1: UP040 [*] Type alias `x` uses `TypeAlias` annotation instead of th
   |
   = help: Use the `type` keyword
 
-ℹ Fix
+ℹ Suggested fix
 3 3 | 
 4 4 | # UP040
 5 5 | x: typing.TypeAlias = int
@@ -52,7 +52,7 @@ UP040.py:10:1: UP040 [*] Type alias `x` uses `TypeAlias` annotation instead of t
    |
    = help: Use the `type` keyword
 
-ℹ Fix
+ℹ Suggested fix
 7  7  | 
 8  8  | # UP040 simple generic
 9  9  | T = typing.TypeVar["T"]
@@ -73,7 +73,7 @@ UP040.py:14:1: UP040 [*] Type alias `x` uses `TypeAlias` annotation instead of t
    |
    = help: Use the `type` keyword
 
-ℹ Fix
+ℹ Suggested fix
 11 11 | 
 12 12 | # UP040 call style generic
 13 13 | T = typing.TypeVar("T")
@@ -94,7 +94,7 @@ UP040.py:18:1: UP040 [*] Type alias `x` uses `TypeAlias` annotation instead of t
    |
    = help: Use the `type` keyword
 
-ℹ Fix
+ℹ Suggested fix
 15 15 | 
 16 16 | # UP040 bounded generic
 17 17 | T = typing.TypeVar("T", bound=int)
@@ -115,7 +115,7 @@ UP040.py:22:1: UP040 [*] Type alias `x` uses `TypeAlias` annotation instead of t
    |
    = help: Use the `type` keyword
 
-ℹ Fix
+ℹ Suggested fix
 19 19 | 
 20 20 | # UP040 constrained generic
 21 21 | T = typing.TypeVar("T", int, str)
@@ -136,7 +136,7 @@ UP040.py:26:1: UP040 [*] Type alias `x` uses `TypeAlias` annotation instead of t
    |
    = help: Use the `type` keyword
 
-ℹ Fix
+ℹ Suggested fix
 23 23 | 
 24 24 | # UP040 contravariant generic
 25 25 | T = typing.TypeVar("T", contravariant=True)
@@ -157,7 +157,7 @@ UP040.py:30:1: UP040 [*] Type alias `x` uses `TypeAlias` annotation instead of t
    |
    = help: Use the `type` keyword
 
-ℹ Fix
+ℹ Suggested fix
 27 27 | 
 28 28 | # UP040 covariant generic
 29 29 | T = typing.TypeVar("T", covariant=True)
@@ -178,7 +178,7 @@ UP040.py:36:5: UP040 [*] Type alias `x` uses `TypeAlias` annotation instead of t
    |
    = help: Use the `type` keyword
 
-ℹ Fix
+ℹ Suggested fix
 33 33 | T = typing.TypeVar["T"]
 34 34 | class Foo:
 35 35 |     # reference to global variable
@@ -199,7 +199,7 @@ UP040.py:40:5: UP040 [*] Type alias `y` uses `TypeAlias` annotation instead of t
    |
    = help: Use the `type` keyword
 
-ℹ Fix
+ℹ Suggested fix
 37 37 | 
 38 38 |     # reference to class variable
 39 39 |     TCLS = typing.TypeVar["TCLS"]
@@ -220,7 +220,7 @@ UP040.py:44:1: UP040 [*] Type alias `x` uses `TypeAlias` annotation instead of t
    |
    = help: Use the `type` keyword
 
-ℹ Fix
+ℹ Suggested fix
 41 41 | 
 42 42 | # UP040 wont add generics in fix
 43 43 | T = typing.TypeVar(*args)

crates/ruff_linter/src/rules/pyupgrade/snapshots/ruff_linter__rules__pyupgrade__tests__UP040.pyi.snap

@@ -0,0 +1,38 @@
+---
+source: crates/ruff_linter/src/rules/pyupgrade/mod.rs
+---
+UP040.pyi:6:1: UP040 [*] Type alias `x` uses `TypeAlias` annotation instead of the `type` keyword
+  |
+4 | # UP040
+5 | # Fixes in type stub files should be safe to apply unlike in regular code where runtime behavior could change
+6 | x: typing.TypeAlias = int
+  | ^^^^^^^^^^^^^^^^^^^^^^^^^ UP040
+7 | x: TypeAlias = int
+  |
+  = help: Use the `type` keyword
+
+ℹ Fix
+3 3 | 
+4 4 | # UP040
+5 5 | # Fixes in type stub files should be safe to apply unlike in regular code where runtime behavior could change
+6   |-x: typing.TypeAlias = int
+  6 |+type x = int
+7 7 | x: TypeAlias = int
+
+UP040.pyi:7:1: UP040 [*] Type alias `x` uses `TypeAlias` annotation instead of the `type` keyword
+  |
+5 | # Fixes in type stub files should be safe to apply unlike in regular code where runtime behavior could change
+6 | x: typing.TypeAlias = int
+7 | x: TypeAlias = int
+  | ^^^^^^^^^^^^^^^^^^ UP040
+  |
+  = help: Use the `type` keyword
+
+ℹ Fix
+4 4 | # UP040
+5 5 | # Fixes in type stub files should be safe to apply unlike in regular code where runtime behavior could change
+6 6 | x: typing.TypeAlias = int
+7   |-x: TypeAlias = int
+  7 |+type x = int
+
+