Fix for invalidating results of a target being removed.

pkg/analyzer/lib/src/task/dart.dart

Index: pkg/analyzer/lib/src/task/dart.dart
diff --git a/pkg/analyzer/lib/src/task/dart.dart b/pkg/analyzer/lib/src/task/dart.dart
index 13af33f185b0d2b2dcb9675a1f7d853a78ad144b..9dc108257b24214576011c40a6aec86e73c1ad97 100644
--- a/pkg/analyzer/lib/src/task/dart.dart
+++ b/pkg/analyzer/lib/src/task/dart.dart
@@ -1302,42 +1302,40 @@ class BuildLibraryElementTask extends SourceBasedAnalysisTask {
         PartDirective partDirective = directive;
         StringLiteral partUri = partDirective.uri;
         Source partSource = partDirective.source;
-        if (context.exists(partSource)) {
-          hasPartDirective = true;
-          CompilationUnit partUnit = partUnitMap[partSource];
-          CompilationUnitElementImpl partElement = partUnit.element;
-          partElement.uriOffset = partUri.offset;
-          partElement.uriEnd = partUri.end;
-          partElement.uri = partDirective.uriContent;
-          //
-          // Validate that the part contains a part-of directive with the same
-          // name as the library.
-          //
-          String partLibraryName =
-              _getPartLibraryName(partSource, partUnit, directivesToResolve);
-          if (partLibraryName == null) {
-            errors.add(new AnalysisError(librarySource, partUri.offset,
-                partUri.length, CompileTimeErrorCode.PART_OF_NON_PART,
-                [partUri.toSource()]));
-          } else if (libraryNameNode == null) {
-            if (partsLibraryName == _UNKNOWN_LIBRARY_NAME) {
-              partsLibraryName = partLibraryName;
-            } else if (partsLibraryName != partLibraryName) {
-              partsLibraryName = null;
-            }
-          } else if (libraryNameNode.name != partLibraryName) {
-            errors.add(new AnalysisError(librarySource, partUri.offset,
-                partUri.length, StaticWarningCode.PART_OF_DIFFERENT_LIBRARY, [
-              libraryNameNode.name,
-              partLibraryName
-            ]));
+        hasPartDirective = true;
+        CompilationUnit partUnit = partUnitMap[partSource];
+        CompilationUnitElementImpl partElement = partUnit.element;
+        partElement.uriOffset = partUri.offset;
+        partElement.uriEnd = partUri.end;
+        partElement.uri = partDirective.uriContent;
+        //
+        // Validate that the part contains a part-of directive with the same
+        // name as the library.
+        //
+        String partLibraryName =
+            _getPartLibraryName(partSource, partUnit, directivesToResolve);
+        if (partLibraryName == null) {
+          errors.add(new AnalysisError(librarySource, partUri.offset,
+              partUri.length, CompileTimeErrorCode.PART_OF_NON_PART,
+              [partUri.toSource()]));
+        } else if (libraryNameNode == null) {
+          if (partsLibraryName == _UNKNOWN_LIBRARY_NAME) {
+            partsLibraryName = partLibraryName;
+          } else if (partsLibraryName != partLibraryName) {
+            partsLibraryName = null;
           }
-          if (entryPoint == null) {
-            entryPoint = _findEntryPoint(partElement);
-          }
-          directive.element = partElement;
-          sourcedCompilationUnits.add(partElement);
+        } else if (libraryNameNode.name != partLibraryName) {
+          errors.add(new AnalysisError(librarySource, partUri.offset,
+              partUri.length, StaticWarningCode.PART_OF_DIFFERENT_LIBRARY, [
+            libraryNameNode.name,
+            partLibraryName
+          ]));
+        }
+        if (entryPoint == null) {
+          entryPoint = _findEntryPoint(partElement);
         }
+        directive.element = partElement;
+        sourcedCompilationUnits.add(partElement);
       }
     }
     if (hasPartDirective && libraryNameNode == null) {