fix: fix PEP 646 support of tuple unpacking (#4440)

This change fixes unpacking a tuple or generic type when *args is a type
variable tuple.

CHANGES.md

@@ -14,6 +14,9 @@
 
 <!-- Changes that affect Black's preview style -->
 
+- Fix type annotation spacing between * and more complex type variable tuple (i.e. `def
+  fn(*args: *tuple[*Ts, T]) -> None: pass`) (#4440)
+
 ### Configuration
 
 <!-- Changes to how Black can be configured -->

docs/the_black_code_style/future_style.md

@@ -36,6 +36,8 @@ Currently, the following features are included in the preview style:
   `case` blocks.
 - `parens_for_long_if_clauses_in_case_block`: Adds parentheses to `if` clauses in `case`
   blocks when the line is too long
+- `pep646_typed_star_arg_type_var_tuple`: fix type annotation spacing between * and more
+  complex type variable tuple (i.e. `def fn(*args: *tuple[*Ts, T]) -> None: pass`)
 
 (labels/unstable-features)=
 

src/black/mode.py

@@ -206,6 +206,7 @@ class Preview(Enum):
     docstring_check_for_newline = auto()
     remove_redundant_guard_parens = auto()
     parens_for_long_if_clauses_in_case_block = auto()
+    pep646_typed_star_arg_type_var_tuple = auto()
 
 
 UNSTABLE_FEATURES: Set[Preview] = {

src/black/nodes.py

@@ -254,9 +254,15 @@ def whitespace(leaf: Leaf, *, complex_subscript: bool, mode: Mode) -> str:  # no
         elif (
             prevp.type == token.STAR
             and parent_type(prevp) == syms.star_expr
-            and parent_type(prevp.parent) == syms.subscriptlist
+            and (
+                parent_type(prevp.parent) == syms.subscriptlist
+                or (
+                    Preview.pep646_typed_star_arg_type_var_tuple in mode
+                    and parent_type(prevp.parent) == syms.tname_star
+                )
+            )
         ):
-            # No space between typevar tuples.
+            # No space between typevar tuples or unpacking them.
             return NO
 
         elif prevp.type in VARARGS_SPECIALS:

src/black/resources/black.schema.json

@@ -90,7 +90,8 @@
           "is_simple_lookup_for_doublestar_expression",
           "docstring_check_for_newline",
           "remove_redundant_guard_parens",
-          "parens_for_long_if_clauses_in_case_block"
+          "parens_for_long_if_clauses_in_case_block",
+          "pep646_typed_star_arg_type_var_tuple"
         ]
       },
       "description": "Enable specific features included in the `--unstable` style. Requires `--preview`. No compatibility guarantees are provided on the behavior or existence of any unstable features."

tests/data/cases/preview_pep646_typed_star_arg_type_var_tuple.py

@@ -0,0 +1,8 @@
+# flags: --minimum-version=3.11 --preview
+
+
+def fn(*args: *tuple[*A, B]) -> None:
+    pass
+
+
+fn.__annotations__

tests/test_black.py

@@ -906,6 +906,9 @@ def test_get_features_used(self) -> None:
         self.check_features_used("a[*b]", {Feature.VARIADIC_GENERICS})
         self.check_features_used("a[x, *y(), z] = t", {Feature.VARIADIC_GENERICS})
         self.check_features_used("def fn(*args: *T): pass", {Feature.VARIADIC_GENERICS})
+        self.check_features_used(
+            "def fn(*args: *tuple[*T]): pass", {Feature.VARIADIC_GENERICS}
+        )
 
         self.check_features_used("with a: pass", set())
         self.check_features_used("with a, b: pass", set())