Avoid syntax errors for type variables with starred constraints (UP040, UP046, UP047, RUF053)

crates/ruff_linter/resources/test/fixtures/pyupgrade/UP040.py

@@ -149,3 +149,10 @@ class Foo:
         | str
     ),
 )
+
+
+# A sole starred constraint needs a trailing comma in the PEP 695 constraint tuple.
+constraints = (int, str)
+T_starred = TypeVar("T_starred", *constraints)
+StarredList: TypeAlias = list[T_starred]
+StarredAlias = TypeAliasType("StarredAlias", list[T_starred], type_params=(T_starred,))

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

@@ -142,3 +142,20 @@ class DefaultOnlyTypeVar(Generic[W]):  # -> [W = int]
 class Outer:
     class Inner(Generic[T]):
         var: T
+
+
+# A sole starred constraint needs a trailing comma in the PEP 695 constraint tuple.
+constraints = (int, str)
+U = TypeVar("U", *constraints)
+
+
+class StarredConstraints(Generic[U]):
+    var: U
+
+
+# Mixed constraints retain both the explicit and unpacked types.
+V = TypeVar("V", bool, *constraints)
+
+
+class MixedConstraints(Generic[V]):
+    var: V

crates/ruff_linter/resources/test/fixtures/pyupgrade/UP047_0.py

@@ -63,3 +63,12 @@ def multi_param(t: list[T], c: Callable[[T], None]) -> T:
 def outer():
     def inner(t: T) -> T:
         return t
+
+
+# A sole starred constraint needs a trailing comma in the PEP 695 constraint tuple.
+constraints = (int, str)
+U = TypeVar("U", *constraints)
+
+
+def starred_constraints(var: U) -> U:
+    return var

crates/ruff_linter/resources/test/fixtures/ruff/RUF053.py

@@ -98,7 +98,16 @@ class C[T: [a]](Generic[_A]): ...
 
 # Existing bounds should not be deparenthesized.
 # class C[T: (_Y := int)](Generic[_A]): ...  # TODO: Uncomment this
-# class C[T: (*a,)](Generic[_A]): ...        # TODO: Uncomment this
+
+
+# A sole starred constraint needs a trailing comma in the PEP 695 constraint tuple.
+constraints = (str, bytes)
+_H = TypeVar('_H', *constraints)
+class C[T](Generic[_H]): ...
+
+
+# Existing starred constraint tuples retain their trailing comma.
+class C[T: (*constraints,)](Generic[_A]): ...
 
 
 ### No errors

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

@@ -119,15 +119,21 @@ impl Display for DisplayTypeVar<'_> {
                 }
                 TypeVarRestriction::AnyStr => f.write_str("(bytes, str)")?,
                 TypeVarRestriction::Constraint(vec) => {
-                    let len = vec.len();
-                    f.write_str("(")?;
-                    for (i, v) in vec.iter().enumerate() {
-                        f.write_str(&self.source[v.range()])?;
-                        if i < len - 1 {
-                            f.write_str(", ")?;
+                    match vec.as_slice() {
+                        // A single starred expression needs a comma to form a constraint tuple:
+                        // `TypeVar("T", *constraints)` becomes `T: (*constraints,)`.
+                        [element] => {
+                            write!(f, "({element},)", element = &self.source[element.range()])?;
+                        }
+                        _ => {
+                            write!(
+                                f,
+                                "({})",
+                                vec.iter()
+                                    .format_with(", ", |expr, f| f(&&self.source[expr.range()])),
+                            )?;
                         }
                     }
-                    f.write_str(")")?;
                 }
             }
         }

crates/ruff_linter/src/rules/pyupgrade/snapshots/ruff_linter__rules__pyupgrade__tests__UP040.py.snap

@@ -497,5 +497,39 @@ help: Use the `type` keyword
     -     ),
     - )
 148 +     )
+149 |
+    |
+note: This is an unsafe fix and may change runtime behavior
+
+UP040 [*] Type alias `StarredList` uses `TypeAlias` annotation instead of the `type` keyword
+   --> UP040.py:157:1
+    |
+155 | constraints = (int, str)
+156 | T_starred = TypeVar("T_starred", *constraints)
+157 | StarredList: TypeAlias = list[T_starred]
+    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+158 | StarredAlias = TypeAliasType("StarredAlias", list[T_starred], type_params=(T_starred,))
+    |
+help: Use the `type` keyword
+    |
+156 | T_starred = TypeVar("T_starred", *constraints)
+    - StarredList: TypeAlias = list[T_starred]
+157 + type StarredList[T_starred: (*constraints,)] = list[T_starred]
+158 | StarredAlias = TypeAliasType("StarredAlias", list[T_starred], type_params=(T_starred,))
+    |
+note: This is an unsafe fix and may change runtime behavior
+
+UP040 [*] Type alias `StarredAlias` uses `TypeAliasType` assignment instead of the `type` keyword
+   --> UP040.py:158:1
+    |
+156 | T_starred = TypeVar("T_starred", *constraints)
+157 | StarredList: TypeAlias = list[T_starred]
+158 | StarredAlias = TypeAliasType("StarredAlias", list[T_starred], type_params=(T_starred,))
+    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+help: Use the `type` keyword
+    |
+157 | StarredList: TypeAlias = list[T_starred]
+    - StarredAlias = TypeAliasType("StarredAlias", list[T_starred], type_params=(T_starred,))
+158 + type StarredAlias[T_starred: (*constraints,)] = list[T_starred]
     |
 note: This is an unsafe fix and may change runtime behavior

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

@@ -253,3 +253,35 @@ UP046 Generic class `TooManyGenerics` uses `Generic` subclass instead of type pa
 100 |     var: S
     |
 help: Use type parameters
+
+UP046 [*] Generic class `StarredConstraints` uses `Generic` subclass instead of type parameters
+   --> UP046_0.py:152:26
+    |
+152 | class StarredConstraints(Generic[U]):
+    |                          ^^^^^^^^^^
+153 |     var: U
+    |
+help: Use type parameters
+    |
+151 |
+    - class StarredConstraints(Generic[U]):
+152 + class StarredConstraints[U: (*constraints,)]:
+153 |     var: U
+    |
+note: This is an unsafe fix and may change runtime behavior
+
+UP046 [*] Generic class `MixedConstraints` uses `Generic` subclass instead of type parameters
+   --> UP046_0.py:160:24
+    |
+160 | class MixedConstraints(Generic[V]):
+    |                        ^^^^^^^^^^
+161 |     var: V
+    |
+help: Use type parameters
+    |
+159 |
+    - class MixedConstraints(Generic[V]):
+160 + class MixedConstraints[V: (bool, *constraints)]:
+161 |     var: V
+    |
+note: This is an unsafe fix and may change runtime behavior

crates/ruff_linter/src/rules/pyupgrade/snapshots/ruff_linter__rules__pyupgrade__tests__UP047_0.py.snap

@@ -122,3 +122,19 @@ help: Use type parameters
 57 |     c(t[0])
    |
 note: This is an unsafe fix and may change runtime behavior
+
+UP047 [*] Generic function `starred_constraints` should use type parameters
+  --> UP047_0.py:73:5
+   |
+73 | def starred_constraints(var: U) -> U:
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+74 |     return var
+   |
+help: Use type parameters
+   |
+72 |
+   - def starred_constraints(var: U) -> U:
+73 + def starred_constraints[U: (*constraints,)](var: U) -> U:
+74 |     return var
+   |
+note: This is an unsafe fix and may change runtime behavior

crates/ruff_linter/src/rules/ruff/snapshots/ruff_linter__rules__ruff__tests__class-with-mixed-type-vars_RUF053.py.snap

@@ -429,7 +429,7 @@ help: Remove `Generic` base class
    |
 94 | # Single-element constraints should not be converted to a bound.
    - class C[T: (str,)](Generic[_A]): ...
-95 + class C[T: (str), _A]: ...
+95 + class C[T: (str,), _A]: ...
 96 | class C[T: [a]](Generic[_A]): ...
    |
 note: This is an unsafe fix and may change runtime behavior
@@ -449,3 +449,34 @@ help: Remove `Generic` base class
 97 |
    |
 note: This is an unsafe fix and may change runtime behavior
+
+RUF053 [*] Class with type parameter list inherits from `Generic`
+   --> RUF053.py:106:12
+    |
+104 | constraints = (str, bytes)
+105 | _H = TypeVar('_H', *constraints)
+106 | class C[T](Generic[_H]): ...
+    |            ^^^^^^^^^^^
+help: Remove `Generic` base class
+    |
+105 | _H = TypeVar('_H', *constraints)
+    - class C[T](Generic[_H]): ...
+106 + class C[T, _H: (*constraints,)]: ...
+107 |
+    |
+note: This is an unsafe fix and may change runtime behavior
+
+RUF053 [*] Class with type parameter list inherits from `Generic`
+   --> RUF053.py:110:29
+    |
+109 | # Existing starred constraint tuples retain their trailing comma.
+110 | class C[T: (*constraints,)](Generic[_A]): ...
+    |                             ^^^^^^^^^^^
+help: Remove `Generic` base class
+    |
+109 | # Existing starred constraint tuples retain their trailing comma.
+    - class C[T: (*constraints,)](Generic[_A]): ...
+110 + class C[T: (*constraints,), _A]: ...
+111 |
+    |
+note: This is an unsafe fix and may change runtime behavior