[flake8-pyi] Avoid flagging custom-typevar-for-self on metaclass methods (PYI019) (#16141)

Author: vladNed

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

@@ -174,3 +174,10 @@ def m[S](self: S) -> S:
         type S = int
         print(S)  # not a reference to the type variable, so not touched by the autofix
         return 42
+
+
+MetaType = TypeVar("MetaType")
+
+class MetaTestClass(type):
+    def m(cls: MetaType) -> MetaType:
+        return cls

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

@@ -165,3 +165,10 @@ class NoReturnAnnotations:
 class MultipleBoundParameters:
     def m[S: int, T: int](self: S, other: T) -> S: ...
     def n[T: (int, str), S: (int, str)](self: S, other: T) -> S: ...
+
+
+MetaType = TypeVar("MetaType")
+
+class MetaTestClass(type):
+    def m(cls: MetaType) -> MetaType:
+        return cls

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

@@ -4,6 +4,7 @@ use itertools::Itertools;
 use ruff_diagnostics::{Applicability, Diagnostic, Edit, Fix, FixAvailability, Violation};
 use ruff_macros::{derive_message_formats, ViolationMetadata};
 use ruff_python_ast as ast;
+use ruff_python_semantic::analyze::class::is_metaclass;
 use ruff_python_semantic::analyze::function_type::{self, FunctionType};
 use ruff_python_semantic::analyze::visibility::{is_abstract, is_overload};
 use ruff_python_semantic::{Binding, ResolvedReference, ScopeId, SemanticModel};
@@ -128,9 +129,14 @@ pub(crate) fn custom_type_var_instead_of_self(
         .next()?;
 
     let self_or_cls_annotation = self_or_cls_parameter.annotation()?;
+    let parent_class = current_scope.kind.as_class()?;
 
-    // Skip any abstract, static, and overloaded methods.
-    if is_abstract(decorator_list, semantic) || is_overload(decorator_list, semantic) {
+    // Skip any abstract/static/overloaded methods,
+    // and any methods in metaclasses
+    if is_abstract(decorator_list, semantic)
+        || is_overload(decorator_list, semantic)
+        || is_metaclass(parent_class, semantic).is_yes()
+    {
         return None;
     }
 

crates/ruff_linter/src/rules/flake8_pyi/snapshots/ruff_linter__rules__flake8_pyi__tests__preview_PYI019_PYI019_0.pyi.snap

@@ -661,6 +661,8 @@ PYI019_0.pyi:166:10: PYI019 [*] Use `Self` instead of custom TypeVar `S`
 166     |-    def m[S: int, T: int](self: S, other: T) -> S: ...
     166 |+    def m[T: int](self, other: T) -> Self: ...
 167 167 |     def n[T: (int, str), S: (int, str)](self: S, other: T) -> S: ...
+168 168 | 
+169 169 | 
 
 PYI019_0.pyi:167:10: PYI019 [*] Use `Self` instead of custom TypeVar `S`
     |
@@ -677,3 +679,6 @@ PYI019_0.pyi:167:10: PYI019 [*] Use `Self` instead of custom TypeVar `S`
 166 166 |     def m[S: int, T: int](self: S, other: T) -> S: ...
 167     |-    def n[T: (int, str), S: (int, str)](self: S, other: T) -> S: ...
     167 |+    def n[T: (int, str)](self, other: T) -> Self: ...
+168 168 | 
+169 169 | 
+170 170 | MetaType = TypeVar("MetaType")