Move attrs PEP 695 variance test to check-python312.test

Tests in check-python312.test get python_version=(3,12) automatically
via testfile_pyversion(), which matches the filename.  The test relied
on # flags: --python-version 3.12 in check-plugin-attrs.test, but that
path has a subtle interaction with mypyc-compiled mypy on Python 3.10
that causes the version flag to be silently ignored, yielding a syntax
error instead of the expected type errors.

Moving the test to check-python312.test (alongside the equivalent frozen-
dataclass test) resolves the failure without changing test semantics.

Assistant-Model: Claude Code

Author: allanlewis

test-data/unit/check-plugin-attrs.test

@@ -2512,41 +2512,3 @@ Parent(run_type = None)
 c = Child(run_type = None)
 reveal_type(c.run_type)  # N: Revealed type is "builtins.int | None"
 [builtins fixtures/plugin_attrs.pyi]
-
-[case testAttrsPEP695InferVariance]
-# flags: --python-version 3.12
-import attrs
-
-# attrs synthesizes ordering dunders (__lt__/__le__/__gt__/__ge__) whose
-# ``other`` parameter is typed as the class's own ``Self[T]``. Those methods are
-# plugin-generated and must not drag T into a contravariant position during
-# PEP 695 variance inference. A frozen class using T only covariantly should be
-# inferred covariant.
-@attrs.frozen
-class Covariant[T]:
-    x: T
-    def get(self) -> T:
-        return self.x
-
-cov1: Covariant[object] = Covariant[int](1)
-cov2: Covariant[int] = Covariant[object](1)  # E: Incompatible types in assignment (expression has type "Covariant[object]", variable has type "Covariant[int]")
-
-# A mutable attribute still makes the class invariant: plugin-generated *fields*
-# must continue to be considered.
-@attrs.define
-class Invariant[T]:
-    x: T
-
-inv1: Invariant[object] = Invariant[int](1)  # E: Incompatible types in assignment (expression has type "Invariant[int]", variable has type "Invariant[object]")
-inv2: Invariant[int] = Invariant[object](1)  # E: Incompatible types in assignment (expression has type "Invariant[object]", variable has type "Invariant[int]")
-
-# A user-written method with T in a parameter must still be honored: only
-# plugin-generated methods are skipped, so this class stays contravariant.
-@attrs.frozen
-class Contravariant[T]:
-    def feed(self, x: T) -> None: ...
-
-con1: Contravariant[int] = Contravariant[object]()
-con2: Contravariant[object] = Contravariant[int]()  # E: Incompatible types in assignment (expression has type "Contravariant[int]", variable has type "Contravariant[object]")
-[builtins fixtures/plugin_attrs.pyi]
-[typing fixtures/typing-full.pyi]

test-data/unit/check-python312.test

@@ -265,6 +265,42 @@ cov2: Covariant[int] = Covariant[float](1)  # E: Incompatible types in assignmen
 [builtins fixtures/tuple.pyi]
 [typing fixtures/typing-full.pyi]
 
+[case testPEP695InferVarianceWithAttrsFrozen]
+import attrs
+
+# attrs synthesizes ordering dunders (__lt__/__le__/__gt__/__ge__) whose
+# ``other`` parameter is typed as the class's own ``Self[T]``. Those methods
+# are plugin-generated and must not drag T into a contravariant position
+# during PEP 695 variance inference. A frozen class using T only covariantly
+# should be inferred covariant.
+@attrs.frozen
+class Covariant[T]:
+    x: T
+    def get(self) -> T:
+        return self.x
+
+cov1: Covariant[object] = Covariant[int](1)
+cov2: Covariant[int] = Covariant[object](1)  # E: Incompatible types in assignment (expression has type "Covariant[object]", variable has type "Covariant[int]")
+
+# A mutable attribute still makes the class invariant.
+@attrs.define
+class Invariant[T]:
+    x: T
+
+inv1: Invariant[object] = Invariant[int](1)  # E: Incompatible types in assignment (expression has type "Invariant[int]", variable has type "Invariant[object]")
+inv2: Invariant[int] = Invariant[object](1)  # E: Incompatible types in assignment (expression has type "Invariant[object]", variable has type "Invariant[int]")
+
+# A user-written method with T in a parameter must still be honored: only
+# plugin-generated methods are skipped, so this class stays contravariant.
+@attrs.frozen
+class Contravariant[T]:
+    def feed(self, x: T) -> None: ...
+
+con1: Contravariant[int] = Contravariant[object]()
+con2: Contravariant[object] = Contravariant[int]()  # E: Incompatible types in assignment (expression has type "Contravariant[int]", variable has type "Contravariant[object]")
+[builtins fixtures/plugin_attrs.pyi]
+[typing fixtures/typing-full.pyi]
+
 [case testPEP695InferVarianceCalculateOnDemand]
 class Covariant[T]:
     def __init__(self) -> None: