[flake8-pyi] Fix false negative for PYI046 with unused generic protoc…

…ols (#9405)

I just fixed this false negative in flake8-pyi
(PyCQA/flake8-pyi#460), and then realised ruff
has the exact same bug! Luckily it's a very easy fix.

(The bug is that unused protocols go undetected if they're generic.)

crates/ruff_linter/resources/test/fixtures/flake8_pyi/PYI046.py

@@ -1,5 +1,5 @@
 import typing
-from typing import Protocol
+from typing import Protocol, TypeVar
 
 
 class _Foo(Protocol):
@@ -10,9 +10,23 @@ class _Bar(typing.Protocol):
     bar: int
 
 
+_T = TypeVar("_T")
+
+
+class _Baz(Protocol[_T]):
+    x: _T
+
+
 # OK
 class _UsedPrivateProtocol(Protocol):
     bar: int
 
 
-def uses__UsedPrivateProtocol(arg: _UsedPrivateProtocol) -> None: ...
+# Also OK
+class _UsedGenericPrivateProtocol(Protocol[_T]):
+    x: _T
+
+
+def uses_some_private_protocols(
+    arg: _UsedPrivateProtocol, arg2: _UsedGenericPrivateProtocol[int]
+) -> None: ...

crates/ruff_linter/resources/test/fixtures/flake8_pyi/PYI046.pyi

@@ -1,5 +1,5 @@
 import typing
-from typing import Protocol
+from typing import Protocol, TypeVar
 
 
 class _Foo(object, Protocol):
@@ -10,9 +10,23 @@ class _Bar(typing.Protocol):
     bar: int
 
 
+_T = TypeVar("_T")
+
+
+class _Baz(Protocol[_T]):
+    x: _T
+
+
 # OK
 class _UsedPrivateProtocol(Protocol):
     bar: int
 
 
-def uses__UsedPrivateProtocol(arg: _UsedPrivateProtocol) -> None: ...
+# Also OK
+class _UsedGenericPrivateProtocol(Protocol[_T]):
+    x: _T
+
+
+def uses_some_private_protocols(
+    arg: _UsedPrivateProtocol, arg2: _UsedGenericPrivateProtocol[int]
+) -> None: ...

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

@@ -1,5 +1,6 @@
 use ruff_diagnostics::{Diagnostic, Violation};
 use ruff_macros::{derive_message_formats, violation};
+use ruff_python_ast::helpers::map_subscript;
 use ruff_python_ast::{self as ast, Expr, Stmt};
 use ruff_python_semantic::Scope;
 use ruff_text_size::Ranged;
@@ -243,11 +244,11 @@ pub(crate) fn unused_private_protocol(
             continue;
         };
 
-        if !class_def
-            .bases()
-            .iter()
-            .any(|base| checker.semantic().match_typing_expr(base, "Protocol"))
-        {
+        if !class_def.bases().iter().any(|base| {
+            checker
+                .semantic()
+                .match_typing_expr(map_subscript(base), "Protocol")
+        }) {
             continue;
         }
 

crates/ruff_linter/src/rules/flake8_pyi/snapshots/ruff_linter__rules__flake8_pyi__tests__PYI046_PYI046.py.snap

@@ -15,4 +15,11 @@ PYI046.py:9:7: PYI046 Private protocol `_Bar` is never used
 10 |     bar: int
    |
 
+PYI046.py:16:7: PYI046 Private protocol `_Baz` is never used
+   |
+16 | class _Baz(Protocol[_T]):
+   |       ^^^^ PYI046
+17 |     x: _T
+   |
+
 

crates/ruff_linter/src/rules/flake8_pyi/snapshots/ruff_linter__rules__flake8_pyi__tests__PYI046_PYI046.pyi.snap

@@ -15,4 +15,11 @@ PYI046.pyi:9:7: PYI046 Private protocol `_Bar` is never used
 10 |     bar: int
    |
 
+PYI046.pyi:16:7: PYI046 Private protocol `_Baz` is never used
+   |
+16 | class _Baz(Protocol[_T]):
+   |       ^^^^ PYI046
+17 |     x: _T
+   |
+