Safe handle removed file while incremental invalidation.

pkg/analyzer/lib/src/context/context.dart

 // Copyright (c) 2015, 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 analyzer.src.context.context;
 
 import 'dart:async';
 import 'dart:collection';
 
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 1870 matching lines @@
           Source librarySource = source;
           // Try to find an old unit which has element model.
           CacheEntry unitEntry =
               getCacheEntry(new LibrarySpecificUnit(librarySource, source));
           CompilationUnit oldUnit = RESOLVED_UNIT_RESULTS
               .skipWhile((result) => result != RESOLVED_UNIT2)
               .map(unitEntry.getValue)
               .firstWhere((unit) => unit != null, orElse: () => null);
           // If we have the old unit, we can try to update it.
           if (oldUnit != null) {
-            CompilationUnit newUnit = parseCompilationUnit(source);
-            IncrementalCompilationUnitElementBuilder builder =
-                new IncrementalCompilationUnitElementBuilder(oldUnit, newUnit);
-            builder.build();
-            CompilationUnitElementDelta unitDelta = builder.unitDelta;
-            if (!unitDelta.hasDirectiveChange) {
-              unitEntry.setValueIncremental(
-                  COMPILATION_UNIT_CONSTANTS, builder.unitConstants, false);
-              DartDelta dartDelta = new DartDelta(source);
-              unitDelta.addedDeclarations.forEach(dartDelta.elementChanged);
-              unitDelta.removedDeclarations.forEach(dartDelta.elementChanged);
-              unitDelta.classDeltas.values.forEach(dartDelta.classChanged);
-              entry.setState(CONTENT, CacheState.INVALID, delta: dartDelta);
-              return;
+            // Safely parse the source.
+            CompilationUnit newUnit;
+            try {
+              newUnit = parseCompilationUnit(source);
+            } catch (_) {
+              // The source might have been removed by this time.
+              // We cannot perform incremental invalidation.
+            }
+            // If the new unit was parsed successfully, continue.
+            if (newUnit != null) {
+              IncrementalCompilationUnitElementBuilder builder =
+                  new IncrementalCompilationUnitElementBuilder(
+                      oldUnit, newUnit);
+              builder.build();
+              CompilationUnitElementDelta unitDelta = builder.unitDelta;
+              if (!unitDelta.hasDirectiveChange) {
+                unitEntry.setValueIncremental(
+                    COMPILATION_UNIT_CONSTANTS, builder.unitConstants, false);
+                DartDelta dartDelta = new DartDelta(source);
+                unitDelta.addedDeclarations.forEach(dartDelta.elementChanged);
+                unitDelta.removedDeclarations.forEach(dartDelta.elementChanged);
+                unitDelta.classDeltas.values.forEach(dartDelta.classChanged);
+                entry.setState(CONTENT, CacheState.INVALID, delta: dartDelta);
+                return;
+              }
             }
           }
         }
       }
       entry.setState(CONTENT, CacheState.INVALID);
       entry.setState(MODIFICATION_TIME, CacheState.INVALID);
       entry.setState(SOURCE_KIND, CacheState.INVALID);
     }
     for (WorkManager workManager in workManagers) {
       workManager.applyChange(
@@ skipping 361 matching lines @@
     }
     DartSdk sdk = factory.dartSdk;
     if (sdk == null) {
       throw new ArgumentError(
           "The source factory for an SDK analysis context must have a DartUriResolver");
     }
     return new AnalysisCache(
         <CachePartition>[AnalysisEngine.instance.partitionManager.forSdk(sdk)]);
   }
 }