Parts. Fix enclosingElement3 for nested parts.

Change-Id: Ifa71541f928fe96139a08c8b5cdc1527e819eac2
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/378577
Reviewed-by: Phil Quitslund <[email protected]>
Commit-Queue: Konstantin Shcheglov <[email protected]>

Author: scheglov

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

@@ -844,17 +844,12 @@ class CompilationUnitElementImpl extends UriReferencedElementImpl
 
   @override
   CompilationUnitElementImpl? get enclosingElement3 {
-    switch (libraryOrAugmentationElement) {
-      case LibraryElementImpl library:
-        if (identical(library.definingCompilationUnit, this)) {
-          return null;
-        }
-        return library.definingCompilationUnit;
-      default:
-        return (libraryOrAugmentationElement.enclosingElement3
-                as LibraryOrAugmentationElementImpl)
-            .definingCompilationUnit;
+    if (libraryOrAugmentationElement is LibraryAugmentationElementImpl) {
+      return (libraryOrAugmentationElement.enclosingElement
+              as LibraryOrAugmentationElementImpl)
+          .definingCompilationUnit;
     }
+    return super.enclosingElement3 as CompilationUnitElementImpl?;
   }
 
   @override

pkg/analyzer/test/src/summary/elements/part_include_test.dart

@@ -139,14 +139,14 @@ library
           enclosingElement: <testLibrary>::@fragment::package:test/a.dart
     <testLibrary>::@fragment::package:test/a11.dart
       enclosingElement: <testLibrary>
-      enclosingElement3: <testLibraryFragment>
+      enclosingElement3: <testLibrary>::@fragment::package:test/a.dart
       classes
         class A11 @24
           reference: <testLibrary>::@fragment::package:test/a11.dart::@class::A11
           enclosingElement: <testLibrary>::@fragment::package:test/a11.dart
     <testLibrary>::@fragment::package:test/a12.dart
       enclosingElement: <testLibrary>
-      enclosingElement3: <testLibraryFragment>
+      enclosingElement3: <testLibrary>::@fragment::package:test/a.dart
       classes
         class A12 @24
           reference: <testLibrary>::@fragment::package:test/a12.dart::@class::A12
@@ -167,14 +167,14 @@ library
           unit: <testLibrary>::@fragment::package:test/b12.dart
     <testLibrary>::@fragment::package:test/b11.dart
       enclosingElement: <testLibrary>
-      enclosingElement3: <testLibraryFragment>
+      enclosingElement3: <testLibrary>::@fragment::package:test/b.dart
       classes
         class B11 @24
           reference: <testLibrary>::@fragment::package:test/b11.dart::@class::B11
           enclosingElement: <testLibrary>::@fragment::package:test/b11.dart
     <testLibrary>::@fragment::package:test/b12.dart
       enclosingElement: <testLibrary>
-      enclosingElement3: <testLibraryFragment>
+      enclosingElement3: <testLibrary>::@fragment::package:test/b.dart
       classes
         class B12 @24
           reference: <testLibrary>::@fragment::package:test/b12.dart::@class::B12