Issue 22962. Adding/removing method/accessor body is a declartion mismatch.

pkg/analyzer/lib/src/generated/element.dart

Index: pkg/analyzer/lib/src/generated/element.dart
diff --git a/pkg/analyzer/lib/src/generated/element.dart b/pkg/analyzer/lib/src/generated/element.dart
index 9a3574cbf59fd2480470cf076fea4a870b75ae56..eb46fe0a1c712120218d73bdb2e1e74c12f876fb 100644
--- a/pkg/analyzer/lib/src/generated/element.dart
+++ b/pkg/analyzer/lib/src/generated/element.dart
@@ -704,7 +704,8 @@ class ClassElementImpl extends ElementImpl implements ClassElement {
     if (isEnum) {
       return getNodeMatching((node) => node is EnumDeclaration);
     } else {
-      return getNodeMatching((node) => node is ClassDeclaration || node is ClassTypeAlias);
+      return getNodeMatching(
+          (node) => node is ClassDeclaration || node is ClassTypeAlias);
     }
   }
 
@@ -3238,6 +3239,12 @@ abstract class ExecutableElement implements Element {
   List<FunctionElement> get functions;
 
   /**
+   * Return `true` if this executable element is abstract.
+   * Executable elements are abstract if they are not external and have no body.
+   */
+  bool get isAbstract;
+
+  /**
    * Return `true` if this executable element has body marked as being
    * asynchronous.
    */
@@ -3382,6 +3389,9 @@ abstract class ExecutableElementImpl extends ElementImpl
   }
 
   @override
+  bool get isAbstract => hasModifier(Modifier.ABSTRACT);
+
+  @override
   bool get isAsynchronous => hasModifier(Modifier.ASYNCHRONOUS);
 
   @override
@@ -3537,6 +3547,9 @@ abstract class ExecutableMember extends Member implements ExecutableElement {
   }
 
   @override
+  bool get isAbstract => baseElement.isAbstract;
+
+  @override
   bool get isAsynchronous => baseElement.isAsynchronous;
 
   @override
@@ -7568,12 +7581,6 @@ abstract class Member implements Element {
  */
 abstract class MethodElement implements ClassMemberElement, ExecutableElement {
   /**
-   * Return `true` if this method is abstract. Methods are abstract if they are
-   * not external and have no body.
-   */
-  bool get isAbstract;
-
-  /**
    * Return the resolved [MethodDeclaration] node that declares this
    * [MethodElement].
    *
@@ -7624,9 +7631,6 @@ class MethodElementImpl extends ExecutableElementImpl implements MethodElement {
   ClassElement get enclosingElement => super.enclosingElement as ClassElement;
 
   @override
-  bool get isAbstract => hasModifier(Modifier.ABSTRACT);
-
-  @override
   bool get isOperator {
     String name = displayName;
     if (name.isEmpty) {
@@ -7698,9 +7702,6 @@ class MethodMember extends ExecutableMember implements MethodElement {
   ClassElement get enclosingElement => baseElement.enclosingElement;
 
   @override
-  bool get isAbstract => baseElement.isAbstract;
-
-  @override
   MethodDeclaration get node => baseElement.node;
 
   @override
@@ -8630,12 +8631,6 @@ abstract class PropertyAccessorElement implements ExecutableElement {
   PropertyAccessorElement get correspondingSetter;
 
   /**
-   * Return `true` if this accessor is abstract. Accessors are abstract if they
-   * are not external and have no body.
-   */
-  bool get isAbstract;
-
-  /**
    * Return `true` if this accessor represents a getter.
    */
   bool get isGetter;
@@ -8727,9 +8722,6 @@ class PropertyAccessorElementImpl extends ExecutableElementImpl
   }
 
   @override
-  bool get isAbstract => hasModifier(Modifier.ABSTRACT);
-
-  @override
   bool get isGetter => hasModifier(Modifier.GETTER);
 
   @override
@@ -8830,9 +8822,6 @@ class PropertyAccessorMember extends ExecutableMember
   Element get enclosingElement => baseElement.enclosingElement;
 
   @override
-  bool get isAbstract => baseElement.isAbstract;
-
-  @override
   bool get isGetter => baseElement.isGetter;
 
   @override