Respect the magic trailing comma in starred type parameter lists

CHANGES.md

@@ -19,6 +19,9 @@
 
 - Fix crash when a standalone comment sits between tokens of a comprehension or lambda
   (#5144)
+- Respect the magic trailing comma in a PEP 695 type parameter list containing a
+  `*TypeVarTuple` or `**ParamSpec`, which previously collapsed back onto one line
+  (#5244)
 - Fix crash when a comment-only `# fmt: off`/`# fmt: on` block is followed by a `with`
   statement after another standalone comment (#5189)
 - Fix a crash when splitting `case case if ...` match patterns at very small line

src/black/nodes.py

@@ -73,6 +73,8 @@
     syms.trailer,  # single argument to call
     syms.typedargslist,
     syms.varargslist,  # lambdas
+    syms.typevartuple,  # star in a PEP 695 type parameter list
+    syms.paramspec,  # double star in a PEP 695 type parameter list
 }
 UNPACKING_PARENTS: Final = {
     syms.atom,  # single element of a list or set literal

tests/data/cases/type_params.py

@@ -13,6 +13,12 @@ def it_gets_worse[WhatIsTheLongestTypeVarNameYouCanThinkOfEnoughToMakeBlackSplit
 
 def magic[Trailing, Comma,](): pass
 
+def magic_starred[T, *Ts, **P,](): pass
+
+class MagicStarred[T, *Ts, **P,]: pass
+
+type MagicStarredAlias[T, *Ts, **P,] = int
+
 def weird_syntax[T: lambda: 42, U: a or b](): pass
 
 def name_3[name_0: aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa if aaaaaaaaaaa else name_3](): pass
@@ -62,6 +68,29 @@ def magic[
     pass
 
 
+def magic_starred[
+    T,
+    *Ts,
+    **P,
+]():
+    pass
+
+
+class MagicStarred[
+    T,
+    *Ts,
+    **P,
+]:
+    pass
+
+
+type MagicStarredAlias[
+    T,
+    *Ts,
+    **P,
+] = int
+
+
 def weird_syntax[T: lambda: 42, U: a or b]():
     pass