If a class's type parameters split, force the clauses to split too.

lib/src/front_end/piece_factory.dart

@@ -805,55 +805,48 @@ mixin PieceFactory {
   void writeImport(NamespaceDirective directive, Token keyword,
       {Token? deferredKeyword, Token? asKeyword, SimpleIdentifier? prefix}) {
     pieces.withMetadata(directive.metadata, () {
-      if (directive.configurations.isEmpty && asKeyword == null) {
-        // If there are no configurations or prefix (the common case), just
-        // write the import directly inline.
+      // Build a piece for the directive itself.
+      var directivePiece = pieces.build(() {
         pieces.token(keyword);
         pieces.space();
         pieces.visit(directive.uri);
-      } else {
-        // Otherwise, allow splitting between the configurations and prefix.
-        var sections = [
-          pieces.build(() {
-            pieces.token(keyword);
-            pieces.space();
-            pieces.visit(directive.uri);
-          })
-        ];
-
-        for (var configuration in directive.configurations) {
-          sections.add(nodePiece(configuration));
-        }
+      });
 
-        if (asKeyword != null) {
-          sections.add(pieces.build(() {
-            pieces.token(deferredKeyword, spaceAfter: true);
-            pieces.token(asKeyword);
-            pieces.space();
-            pieces.visit(prefix!);
-          }));
-        }
+      // Include any `if` clauses.
+      var clauses = <Piece>[];
+      for (var configuration in directive.configurations) {
+        clauses.add(nodePiece(configuration));
+      }
 
-        pieces.add(InfixPiece(const [], sections));
+      // Include the `as` clause.
+      if (asKeyword != null) {
+        clauses.add(pieces.build(() {
+          pieces.token(deferredKeyword, spaceAfter: true);
+          pieces.token(asKeyword);
+          pieces.space();
+          pieces.visit(prefix!);
+        }));
       }
 
-      if (directive.combinators.isNotEmpty) {
-        var combinators = <Piece>[];
-        for (var combinatorNode in directive.combinators) {
-          switch (combinatorNode) {
-            case HideCombinator(hiddenNames: var names):
-            case ShowCombinator(shownNames: var names):
-              combinators.add(InfixPiece(const [], [
-                tokenPiece(combinatorNode.keyword),
-                for (var name in names)
-                  tokenPiece(name.token, commaAfter: true),
-              ]));
-            default:
-              throw StateError('Unknown combinator type $combinatorNode.');
-          }
+      // Include the `show` and `hide` clauses.
+      for (var combinatorNode in directive.combinators) {
+        switch (combinatorNode) {
+          case HideCombinator(hiddenNames: var names):
+          case ShowCombinator(shownNames: var names):
+            clauses.add(InfixPiece(const [], [
+              tokenPiece(combinatorNode.keyword),
+              for (var name in names) tokenPiece(name.token, commaAfter: true),
+            ]));
+          default:
+            throw StateError('Unknown combinator type $combinatorNode.');
         }
+      }
 
-        pieces.add(ClausePiece(combinators));
+      // If there are clauses, include them.
+      if (clauses.isNotEmpty) {
+        pieces.add(ClausePiece(directivePiece, clauses));
+      } else {
+        pieces.add(directivePiece);
       }
 
       pieces.token(directive.semicolon);
@@ -1245,16 +1238,12 @@ mixin PieceFactory {
             [if (nativeClause.name case var name?) name]);
       }
 
-      ClausePiece? clausesPiece;
       if (clauses.isNotEmpty) {
-        clausesPiece = ClausePiece(clauses,
+        header = ClausePiece(header, clauses,
             allowLeadingClause: extendsClause != null || onClause != null);
       }
 
-      var bodyPiece = body();
-
-      pieces
-          .add(TypePiece(header, clausesPiece, bodyPiece, bodyType: bodyType));
+      pieces.add(TypePiece(header, body(), bodyType: bodyType));
     });
   }
 

lib/src/piece/clause.dart

@@ -65,6 +65,10 @@ class ClausePiece extends Piece {
   /// State where we split between the clauses but not before the first one.
   static const State _betweenClauses = State(1);
 
+  /// The leading construct the clauses are applied to: a class declaration,
+  /// import directive, etc.
+  final Piece _header;
+
   final List<Piece> _clauses;
 
   /// If `true`, then we're allowed to split between the clauses without
@@ -80,7 +84,7 @@ class ClausePiece extends Piece {
   ///     }
   final bool _allowLeadingClause;
 
-  ClausePiece(this._clauses, {bool allowLeadingClause = false})
+  ClausePiece(this._header, this._clauses, {bool allowLeadingClause = false})
       : _allowLeadingClause = allowLeadingClause && _clauses.length > 1;
 
   @override
@@ -89,7 +93,10 @@ class ClausePiece extends Piece {
 
   @override
   bool allowNewlineInChild(State state, Piece child) {
-    if (_allowLeadingClause && child == _clauses.first) {
+    if (child == _header) {
+      // If the header splits, force the clauses to split too.
+      return state == State.split;
+    } else if (_allowLeadingClause && child == _clauses.first) {
       // A split inside the first clause forces a split before the keyword.
       return state == State.split;
     } else {
@@ -101,6 +108,8 @@ class ClausePiece extends Piece {
 
   @override
   void format(CodeWriter writer, State state) {
+    writer.format(_header);
+
     writer.pushIndent(Indent.expression);
 
     for (var clause in _clauses) {
@@ -123,6 +132,7 @@ class ClausePiece extends Piece {
 
   @override
   void forEachChild(void Function(Piece piece) callback) {
+    callback(_header);
     _clauses.forEach(callback);
   }
 }

lib/src/piece/type.dart

@@ -2,27 +2,23 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 import '../back_end/code_writer.dart';
-import 'clause.dart';
 import 'piece.dart';
 
 /// Piece for a type declaration with a body containing members.
 ///
 /// Used for class, enum, and extension declarations.
 class TypePiece extends Piece {
-  /// The leading keywords and modifiers, type name, and type parameters.
+  /// The leading keywords and modifiers, type name, type parameters, and any
+  /// other `extends`, `with`, etc. clauses.
   final Piece _header;
 
-  /// The `extends`, `with`, and/or `implements` clauses, if there are any.
-  final ClausePiece? _clauses;
-
   /// The `native` clause, if any, and the type body.
   final Piece _body;
 
   /// What kind of body the type has.
   final TypeBodyType _bodyType;
 
-  TypePiece(this._header, this._clauses, this._body,
-      {required TypeBodyType bodyType})
+  TypePiece(this._header, this._body, {required TypeBodyType bodyType})
       : _bodyType = bodyType;
 
   @override
@@ -47,18 +43,13 @@ class TypePiece extends Piece {
   @override
   void format(CodeWriter writer, State state) {
     writer.format(_header);
-    if (_clauses case var clauses?) {
-      writer.format(clauses);
-    }
-
     if (_bodyType != TypeBodyType.semicolon) writer.space();
     writer.format(_body);
   }
 
   @override
   void forEachChild(void Function(Piece piece) callback) {
     callback(_header);
-    if (_clauses case var clauses?) callback(clauses);
     callback(_body);
   }
 }

test/tall/declaration/class_clause.unit

@@ -251,4 +251,21 @@ class C extends A
         B<
           LongTypeArgument,
           AnotherLongType
-        > {}
+        > {}
+>>> Split in class type parameters forces clause to split.
+class C<LongTypeParameter, AnotherLongType> extends Other {}
+<<<
+class C<
+  LongTypeParameter,
+  AnotherLongType
+>
+    extends Other {}
+>>> Split in class type parameters forces clauses to split.
+class C<LongTypeParameter, AnotherLongType> extends Other with Mixin {}
+<<<
+class C<
+  LongTypeParameter,
+  AnotherLongType
+>
+    extends Other
+    with Mixin {}

test/tall/declaration/extension.unit

@@ -35,7 +35,8 @@ extension Extension<LongTypeParameter, Another> on BaseClass {}
 extension Extension<
   LongTypeParameter,
   Another
-> on BaseClass {}
+>
+    on BaseClass {}
 >>> Unnamed.
 extension on String {}
 <<<

test/tall/declaration/extension_type.unit

@@ -48,7 +48,8 @@ extension type LongExtensionType(LongTypeName a) implements Something {
 <<<
 extension type LongExtensionType(
   LongTypeName a,
-) implements Something {
+)
+    implements Something {
   method() {
     ;
   }

test/tall/regression/other/misc.unit

@@ -19,4 +19,21 @@ SomeVeryLongReturnType someFunctionName(
         })
         .then(________traverseDeps_depender__deps_);
   }
+}
+>>> Split in long type parameter clause.
+abstract class StreamNotifierProviderBase<
+  NotifierT extends AsyncNotifierBase<T>,
+  T
+> extends ProviderWithNotifier<AsyncValue<T>, NotifierT>
+    with FutureModifier<T> {
+  // ...
+}
+<<<
+abstract class StreamNotifierProviderBase<
+  NotifierT extends AsyncNotifierBase<T>,
+  T
+>
+    extends ProviderWithNotifier<AsyncValue<T>, NotifierT>
+    with FutureModifier<T> {
+  // ...
 }