Elements. Add PrefixElementExtension.asElement2 and PrefixElement2Extension.asElement.

Change-Id: I76ae659a487392ddcfffa45c7cf2178ee8ca1b85
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/396623
Reviewed-by: Brian Wilkerson <[email protected]>
Commit-Queue: Konstantin Shcheglov <[email protected]>

Author: scheglov

pkg/analysis_server/lib/src/services/completion/dart/declaration_helper.dart

@@ -340,7 +340,7 @@ class DeclarationHelper {
         collector.addSuggestion(
           ImportPrefixSuggestion(
             libraryElement: importedLibrary.asElement2 as LibraryElement2,
-            prefixElement: prefixElement.asElement2 as PrefixElement2,
+            prefixElement: prefixElement.asElement2,
             matcherScore: matcherScore,
           ),
         );

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

@@ -9097,6 +9097,10 @@ class PrefixElementImpl2 extends ElementImpl2 implements PrefixElement2 {
     reference.element2 = this;
   }
 
+  PrefixElementImpl get asElement {
+    return imports.first.prefix!.element;
+  }
+
   @override
   Null get enclosingElement2 => null;
 

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

@@ -68,8 +68,6 @@ extension Element2OrNullExtension on Element2? {
         return element2.asElement;
       case NeverElementImpl2():
         return NeverElementImpl.instance;
-      case PrefixElementImpl():
-        return self;
       case SetterElementImpl():
         return self.firstFragment as Element;
       case TopLevelFunctionElementImpl():
@@ -333,6 +331,18 @@ extension ParameterElementExtension on ParameterElement {
   }
 }
 
+extension PrefixElement2Extension on PrefixElement2 {
+  PrefixElement get asElement {
+    return (this as PrefixElementImpl2).asElement;
+  }
+}
+
+extension PrefixElementExtension on PrefixElement {
+  PrefixElement2 get asElement2 {
+    return (this as PrefixElementImpl).element2;
+  }
+}
+
 extension TypeParameterElement2Extension on TypeParameterElement2 {
   TypeParameterElement get asElement {
     return firstFragment as TypeParameterElement;