[cfe] Generate covariant checks in pattern matching

Closes #52192

Change-Id: Iaac816273fb80eaf166fc300b2b3367f1a592d3f
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/302223
Commit-Queue: Johnni Winther <johnniwinther@google.com>
Reviewed-by: Chloe Stefantsova <cstefantsova@google.com>

pkg/kernel/lib/src/ast/patterns.dart

@@ -1088,6 +1088,11 @@ class NamedPattern extends Pattern {
   /// This is set during inference.
   DartType? resultType;
 
+  /// When used in an object pattern, this is set to `true` if the field value
+  /// needs to be checked against the [resultType]. This is needed for fields
+  /// whose type contain covariant types that occur in non-covariant positions.
+  bool checkReturn = false;
+
   /// When used in an object pattern, this holds the record on which the
   /// property for this pattern is read.
   ///

pkg/kernel/lib/src/equivalence.dart

@@ -4917,6 +4917,9 @@ class EquivalenceStrategy {
     if (!checkNamedPattern_resultType(visitor, node, other)) {
       result = visitor.resultOnInequivalence;
     }
+    if (!checkNamedPattern_checkReturn(visitor, node, other)) {
+      result = visitor.resultOnInequivalence;
+    }
     if (!checkNamedPattern_recordType(visitor, node, other)) {
       result = visitor.resultOnInequivalence;
     }
@@ -9149,6 +9152,12 @@ class EquivalenceStrategy {
     return visitor.checkNodes(node.resultType, other.resultType, 'resultType');
   }
 
+  bool checkNamedPattern_checkReturn(
+      EquivalenceVisitor visitor, NamedPattern node, NamedPattern other) {
+    return visitor.checkValues(
+        node.checkReturn, other.checkReturn, 'checkReturn');
+  }
+
   bool checkNamedPattern_recordType(
       EquivalenceVisitor visitor, NamedPattern node, NamedPattern other) {
     return visitor.checkNodes(node.recordType, other.recordType, 'recordType');