Issue 25542. If an element does not have its own documentation, use the documentation from the over…

pkg/analysis_server/lib/src/computer/computer_hover.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // 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.
 
 library computer.hover;
 
 import 'package:analysis_server/plugin/protocol/protocol.dart'
     show HoverInformation;
+import 'package:analysis_server/src/computer/computer_overrides.dart';
 import 'package:analysis_server/src/utilities/documentation.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/element.dart';
 
 /**
  * A computer for the hover at the specified offset of a Dart [CompilationUnit].
  */
 class DartUnitHoverComputer {
   final CompilationUnit _unit;
@@ skipping 43 matching lines @@
           if (containingClass != null) {
             hover.containingClassDescription = containingClass.displayName;
           }
           // containing library
           LibraryElement library = element.library;
           if (library != null) {
             hover.containingLibraryName = library.name;
             hover.containingLibraryPath = library.source.fullName;
           }
         }
-
         // documentation
         hover.dartdoc = _computeDocumentation(element);
       }
       // parameter
       hover.parameter = _safeToString(expression.bestParameterElement);
       // types
       if (element == null || element is VariableElement) {
         hover.staticType = _safeToString(expression.staticType);
       }
       hover.propagatedType = _safeToString(expression.propagatedType);
       // done
       return hover;
     }
     // not an expression
     return null;
   }
 
   String _computeDocumentation(Element element) {
     if (element is ParameterElement) {
       element = element.enclosingElement;
     }
-    return removeDartDocDelimiters(element.documentationComment);
+    // The documentation of the element itself.
+    if (element.documentationComment != null) {
+      return removeDartDocDelimiters(element.documentationComment);
+    }
+    // Look for documentation comments of overridden members.
+    OverriddenElements overridden = findOverriddenElements(element);
+    for (Element superElement in []
+      ..addAll(overridden.superElements)
+      ..addAll(overridden.interfaceElements)) {
+      String rawDoc = superElement.documentationComment;
+      if (rawDoc != null) {
+        Element interfaceClass = superElement.enclosingElement;
+        return removeDartDocDelimiters(rawDoc) +
+            '\n\nCopied from `${interfaceClass.displayName}`.';
+      }
+    }
+    return null;
   }
 
   static _safeToString(obj) => obj != null ? obj.toString() : null;
 }