[pyupgrade] Handle multiple base classes for PEP 695 generics (UP046)

crates/ruff_linter/resources/test/fixtures/pyupgrade/UP046_0.py

@@ -71,11 +71,6 @@ def more_generic(u: U, t: T) -> tuple[U, T]:
         return (u, t)
 
 
-# TODO(brent) we should also handle multiple base classes
-class Multiple(NotGeneric, Generic[T]):
-    pass
-
-
 # TODO(brent) default requires 3.13
 V = TypeVar("V", default=Any, bound=str)
 

crates/ruff_linter/src/rules/pyupgrade/rules/pep695/non_pep695_generic_class.rs

@@ -21,10 +21,9 @@ use super::{check_type_vars, in_nested_context, DisplayTypeVars, TypeVarReferenc
 ///
 /// ## Known problems
 ///
-/// The rule currently skips generic classes with multiple base classes. It also skips
-/// generic classes nested inside of other
-/// functions or classes. Finally, this rule skips type parameters with the `default` argument
-/// introduced in [PEP 696] and implemented in Python 3.13.
+/// The rule currently skips generic classes nested inside of other functions or classes. It also
+/// skips type parameters with the `default` argument introduced in [PEP 696] and implemented in
+/// Python 3.13.
 ///
 /// This rule can only offer a fix if all of the generic types in the class definition are defined
 /// in the current module. For external type parameters, a diagnostic is emitted without a suggested
@@ -65,6 +64,10 @@ use super::{check_type_vars, in_nested_context, DisplayTypeVars, TypeVarReferenc
 /// [`unused-private-type-var`](unused-private-type-var.md) for a rule to clean up unused
 /// private type variables.
 ///
+/// This rule will correctly handle classes with multiple base classes, as long as the single
+/// `Generic` base class is at the end of the argument list, as checked by
+/// [`generic-not-last-base-class`](generic-not-last-base-class.md).
+///
 /// This rule only applies to generic classes and does not include generic functions. See
 /// [`non-pep695-generic-function`](non-pep695-generic-function.md) for the function version.
 ///
@@ -118,9 +121,9 @@ pub(crate) fn non_pep695_generic_class(checker: &mut Checker, class_def: &StmtCl
         return;
     };
 
-    // TODO(brent) only accept a single, Generic argument for now. I think it should be fine to have
-    // other arguments, but this simplifies the fix just to delete the argument list for now
-    let [Expr::Subscript(ExprSubscript {
+    // only handle the case where Generic is at the end of the argument list, in line with PYI059
+    // (generic-not-last-base-class)
+    let [base_classes @ .., Expr::Subscript(ExprSubscript {
         value,
         slice,
         range,
@@ -179,11 +182,32 @@ pub(crate) fn non_pep695_generic_class(checker: &mut Checker, class_def: &StmtCl
             source: checker.source(),
         };
 
-        diagnostic.set_fix(Fix::unsafe_edit(Edit::replacement(
-            type_params.to_string(),
-            name.end(),
-            arguments.end(),
-        )));
+        if base_classes.is_empty() {
+            // avoid debug_assert for empty range_replacement by using range_deletion here
+            diagnostic.set_fix(Fix::unsafe_edits(
+                Edit::insertion(type_params.to_string(), name.end()),
+                [Edit::range_deletion(arguments.range)],
+            ));
+        } else {
+            // also build the replacement argument list as a String, if there are any remaining base
+            // classes
+            let base_classes = {
+                let mut s = String::from("(");
+                for (i, arg) in base_classes.iter().enumerate() {
+                    s.push_str(&checker.source()[arg.range()]);
+                    if i < base_classes.len() - 1 {
+                        s.push_str(", ");
+                    }
+                }
+                s.push(')');
+                s
+            };
+
+            diagnostic.set_fix(Fix::unsafe_edits(
+                Edit::insertion(type_params.to_string(), name.end()),
+                [Edit::range_replacement(base_classes, arguments.range)],
+            ));
+        };
     }
 
     checker.diagnostics.push(diagnostic);

crates/ruff_linter/src/rules/pyupgrade/snapshots/ruff_linter__rules__pyupgrade__tests__UP046_0.py.snap

@@ -124,3 +124,21 @@ UP046_0.py:41:24: UP046 [*] Generic class `MultipleGenerics` uses `Generic` subc
 42 42 |     var: S
 43 43 |     typ: T
 44 44 |     tup: tuple[*Ts]
+
+UP046_0.py:48:33: UP046 [*] Generic class `MultipleBaseClasses` uses `Generic` subclass instead of type parameters
+   |
+48 | class MultipleBaseClasses(list, Generic[T]):
+   |                                 ^^^^^^^^^^ UP046
+49 |     var: T
+   |
+   = help: Use type parameters
+
+ℹ Unsafe fix
+45 45 |     pep: P
+46 46 | 
+47 47 | 
+48    |-class MultipleBaseClasses(list, Generic[T]):
+   48 |+class MultipleBaseClasses[T: float](list):
+49 49 |     var: T
+50 50 | 
+51 51 |