[analysis_server] AddExplicitCast to handle toSet

Bug: #49896
Change-Id: I8fdbe33c3e0c5af9f39324b7c537a85a55a918d1
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/259700
Commit-Queue: Brian Wilkerson <brianwilkerson@google.com>
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>

pkg/analysis_server/lib/src/services/correction/dart/add_explicit_cast.dart

@@ -49,8 +49,7 @@ class AddExplicitCast extends CorrectionProducer {
       // because it's nullable, in which case a cast won't fix the problem.
       return;
     }
-    // TODO(brianwilkerson) Handle `toSet` in a manner similar to the below.
-    if (target.isToListMethodInvocation) {
+    if (target.isToListMethodInvocation || target.isToSetMethodInvocation) {
       var targetTarget = (target as MethodInvocation).target;
       if (targetTarget != null) {
         var targetTargetType = targetTarget.typeOrThrow;
@@ -71,12 +70,11 @@ class AddExplicitCast extends CorrectionProducer {
     final target_final = target;
 
     var needsParentheses = target.precedence < Precedence.postfix;
-    if (((fromType.isDartCoreIterable || fromType.isDartCoreList) &&
-            toType is InterfaceType &&
-            toType.isDartCoreList) ||
-        (fromType.isDartCoreSet &&
-            toType is InterfaceType &&
-            toType.isDartCoreSet)) {
+    if (toType is InterfaceType &&
+        (((fromType.isDartCoreIterable || fromType.isDartCoreList) &&
+                toType.isDartCoreList) ||
+            (fromType.isDartCoreIterable || fromType.isDartCoreSet) &&
+                toType.isDartCoreSet)) {
       if (target.isCastMethodInvocation) {
         // TODO(brianwilkerson) Consider updating the type arguments to the
         // `cast` invocation.

pkg/analysis_server/lib/src/utilities/extensions/ast.dart

@@ -180,7 +180,7 @@ extension ExpressionExtensions on Expression {
   }
 
   /// Return `true` if this expression is an invocation of the method `toList`
-  /// from either `Iterable` or `List`.
+  /// from `Iterable`.
   bool get isToListMethodInvocation {
     if (this is MethodInvocation) {
       var element = (this as MethodInvocation).methodName.staticElement;
@@ -188,6 +188,16 @@ extension ExpressionExtensions on Expression {
     }
     return false;
   }
+
+  /// Return `true` if this expression is an invocation of the method `toSet`
+  /// from `Iterable`.
+  bool get isToSetMethodInvocation {
+    if (this is MethodInvocation) {
+      var element = (this as MethodInvocation).methodName.staticElement;
+      return element is MethodElement && element.isToSetMethod;
+    }
+    return false;
+  }
 }
 
 extension FunctionBodyExtensions on FunctionBody {

pkg/analysis_server/lib/src/utilities/extensions/element.dart

@@ -79,8 +79,8 @@ extension MethodElementExtensions on MethodElement {
         definingClass.isDartCoreSet;
   }
 
-  /// Return `true` if this element represents the method `toList` from either
-  /// `Iterable` or `List`.
+  /// Return `true` if this element represents the method `toList` from
+  /// `Iterable`.
   bool get isToListMethod {
     if (name != 'toList') {
       return false;
@@ -89,6 +89,19 @@ extension MethodElementExtensions on MethodElement {
     if (definingClass is! ClassElement) {
       return false;
     }
-    return definingClass.isDartCoreIterable || definingClass.isDartCoreList;
+    return definingClass.isDartCoreIterable;
+  }
+
+  /// Return `true` if this element represents the method `toSet` from
+  /// `Iterable`.
+  bool get isToSetMethod {
+    if (name != 'toSet') {
+      return false;
+    }
+    var definingClass = enclosingElement3;
+    if (definingClass is! ClassElement) {
+      return false;
+    }
+    return definingClass.isDartCoreIterable;
   }
 }

pkg/analysis_server/test/src/services/correction/fix/add_explicit_cast_test.dart

@@ -76,6 +76,27 @@ class B {}
 ''');
   }
 
+  Future<void> test_assignment_iterable_to_set() async {
+    await resolveTestCode('''
+f(List<A> a) {
+  Set<B> b;
+  b = a.where((e) => e is B).toSet();
+  print(b);
+}
+class A {}
+class B {}
+''');
+    await assertHasFix('''
+f(List<A> a) {
+  Set<B> b;
+  b = a.where((e) => e is B).cast<B>().toSet();
+  print(b);
+}
+class A {}
+class B {}
+''');
+  }
+
   Future<void> test_assignment_list() async {
     await resolveTestCode('''
 f(List<A> a) {