check legacy vs inherited

Author: dcreager

crates/red_knot_python_semantic/resources/mdtest/generics/legacy/classes.md

@@ -62,12 +62,12 @@ if you do, you have to mention all of the typevars that you use in your other ba
 ```py
 class ExplicitInheritedGeneric(MultipleTypevars[T, S], Generic[T, S]): ...
 
-# TODO: error
+# error: [invalid-generic-class] "`Generic` base class must include all type variables used in other base classes"
 class ExplicitInheritedGenericMissingTypevar(MultipleTypevars[T, S], Generic[T]): ...
 class ExplicitInheritedGenericPartiallySpecialized(MultipleTypevars[T, int], Generic[T]): ...
 class ExplicitInheritedGenericPartiallySpecializedExtraTypevar(MultipleTypevars[T, int], Generic[T, S]): ...
 
-# TODO: error
+# error: [invalid-generic-class] "`Generic` base class must include all type variables used in other base classes"
 class ExplicitInheritedGenericPartiallySpecializedMissingTypevar(MultipleTypevars[T, int], Generic[S]): ...
 
 reveal_type(generic_context(ExplicitInheritedGeneric))  # revealed: tuple[T, S]

crates/red_knot_python_semantic/src/types/generics.rs

@@ -1,3 +1,4 @@
+use itertools::Itertools;
 use ruff_python_ast as ast;
 use rustc_hash::FxHashMap;
 
@@ -147,6 +148,15 @@ impl<'db> GenericContext<'db> {
         self.specialize(db, types.into())
     }
 
+    pub(crate) fn is_subset_of(self, db: &'db dyn Db, other: GenericContext<'db>) -> bool {
+        for variable in self.variables(db) {
+            if !other.variables(db).iter().contains(variable) {
+                return false;
+            }
+        }
+        true
+    }
+
     pub(crate) fn specialize(
         self,
         db: &'db dyn Db,

crates/red_knot_python_semantic/src/types/infer.rs

@@ -978,7 +978,8 @@ impl<'db> TypeInferenceBuilder<'db> {
                 }
             }
 
-            // (5) Check that a generic class does not use both PEP-695 and legacy syntax.
+            // (5) Check that a generic class does not have invalid or conflicting generic
+            // contexts.
             if class.pep695_generic_context(self.db()).is_some()
                 && class.legacy_generic_context(self.db()).is_some()
             {
@@ -989,6 +990,22 @@ impl<'db> TypeInferenceBuilder<'db> {
                     );
                 }
             }
+
+            if let (Some(legacy), Some(inherited)) = (
+                class.legacy_generic_context(self.db()),
+                class.inherited_legacy_generic_context(self.db()),
+            ) {
+                if !inherited.is_subset_of(self.db(), legacy) {
+                    if let Some(builder) =
+                        self.context.report_lint(&INVALID_GENERIC_CLASS, class_node)
+                    {
+                        builder.into_diagnostic(
+                            "`Generic` base class must include all type \
+                            variables used in other base classes",
+                        );
+                    }
+                }
+            }
         }
     }