The parameter of synthetic setters should inherit 'covariant'.

pkg/analyzer/lib/src/summary/idl.dart

Index: pkg/analyzer/lib/src/summary/idl.dart
diff --git a/pkg/analyzer/lib/src/summary/idl.dart b/pkg/analyzer/lib/src/summary/idl.dart
index 3f365dc1673ea54729eaa65dda61e5067d0f4472..b59f7a169c000df065e1bd2d69870ca4a6e16f5c 100644
--- a/pkg/analyzer/lib/src/summary/idl.dart
+++ b/pkg/analyzer/lib/src/summary/idl.dart
@@ -824,9 +824,9 @@ abstract class LinkedUnit extends base.SummaryClass {
   List<int> get constCycles;
 
   /**
-   * List of slot ids (referring to [UnlinkedParam.inheritsCovariantSlot])
-   * corresponding to parameters that inherit `@covariant` behavior from a base
-   * class.
+   * List of slot ids (referring to [UnlinkedParam.inheritsCovariantSlot] or
+   * [UnlinkedVariable.inheritsCovariantSlot]) corresponding to parameters
+   * that inherit `@covariant` behavior from a base class.
    */
   @Id(3)
   List<int> get parametersInheritingCovariant;
@@ -3224,6 +3224,17 @@ abstract class UnlinkedVariable extends base.SummaryClass {
   int get inferredTypeSlot;
 
   /**
+   * If this is an instance non-final field, a nonzero slot id which is unique
+   * within this compilation unit.  If this id is found in
+   * [LinkedUnit.parametersInheritingCovariant], then the parameter of the
+   * synthetic setter inherits `@covariant` behavior from a base class.
+   *
+   * Otherwise, zero.
+   */
+  @Id(15)
+  int get inheritsCovariantSlot;
+
+  /**
    * The synthetic initializer function of the variable.  Absent if the variable
    * does not have an initializer.
    */