[flake8-pyi] Significantly improve accuracy of PYI019 if preview …

…mode is enabled

crates/ruff_linter/resources/test/fixtures/flake8_pyi/PYI019_0.py

@@ -111,4 +111,27 @@ def m[S](cls: type[S]) -> S: ...  # no error here
 
 class SubscriptReturnType:
     @classmethod
-    def m[S](cls: type[S]) -> type[S]: ...  # PYI019, but no autofix (yet)
+    def m[S](cls: type[S]) -> type[S]: ...  # PYI019
+
+
+class SelfNotUsedInReturnAnnotation:
+    def m[S](self: S, other: S) -> int: ...
+    @classmethod
+    def n[S](cls: type[S], other: S) -> int: ...
+
+
+class _NotATypeVar: ...
+
+# Our stable-mode logic uses heuristics and thinks this is a `TypeVar`
+# because `self` and the return annotation use the same name as their annotation,
+# but our preview-mode logic is smarter about this.
+class Foo:
+    def x(self: _NotATypeVar) -> _NotATypeVar: ...
+    @classmethod
+    def y(self: type[_NotATypeVar]) -> _NotATypeVar: ...
+
+
+class NoReturnAnnotations:
+    def m[S](self: S, other: S): ...
+    @classmethod
+    def n[S](cls: type[S], other: S): ...

crates/ruff_linter/resources/test/fixtures/flake8_pyi/PYI019_0.pyi

@@ -111,7 +111,7 @@ def shadowed_type():
 
 class SubscriptReturnType:
     @classmethod
-    def m[S](cls: type[S]) -> type[S]: ...  # PYI019, but no autofix (yet)
+    def m[S](cls: type[S]) -> type[S]: ...  # PYI019
 
 
 class PEP695TypeParameterAtTheVeryEndOfTheList:
@@ -139,3 +139,25 @@ class PEP695Again:
             S, T
         ]
     ) -> S: ...
+
+
+class SelfNotUsedInReturnAnnotation:
+    def m[S](self: S, other: S) -> int: ...
+    @classmethod
+    def n[S](cls: type[S], other: S) -> int: ...
+
+
+class _NotATypeVar: ...
+
+# Our stable-mode logic uses heuristics and thinks this is a `TypeVar`
+# because `self` and the return annotation use the same name as their annotation,
+# but our preview-mode logic is smarter about this.
+class Foo:
+    def x(self: _NotATypeVar) -> _NotATypeVar: ...
+    @classmethod
+    def y(self: type[_NotATypeVar]) -> _NotATypeVar: ...
+
+class NoReturnAnnotations:
+    def m[S](self: S, other: S): ...
+    @classmethod
+    def n[S](cls: type[S], other: S): ...

crates/ruff_linter/src/rules/flake8_pyi/mod.rs

@@ -155,6 +155,7 @@ mod tests {
         Ok(())
     }
 
+    #[test_case(Rule::CustomTypeVarForSelf, Path::new("PYI019_0.py"))]
     #[test_case(Rule::CustomTypeVarForSelf, Path::new("PYI019_0.pyi"))]
     #[test_case(Rule::CustomTypeVarForSelf, Path::new("PYI019_1.pyi"))]
     fn custom_classmethod_rules_preview(rule_code: Rule, path: &Path) -> Result<()> {