Fix cache corruption in incremental resolver

pkg/analyzer/test/generated/incremental_resolver_test.dart

Index: pkg/analyzer/test/generated/incremental_resolver_test.dart
diff --git a/pkg/analyzer/test/generated/incremental_resolver_test.dart b/pkg/analyzer/test/generated/incremental_resolver_test.dart
index 5c52f176d18ffb7bf8479351fc83de08194bc62a..9ee7ea183e1d5f3e57322c7b85c419529ebfb01c 100644
--- a/pkg/analyzer/test/generated/incremental_resolver_test.dart
+++ b/pkg/analyzer/test/generated/incremental_resolver_test.dart
@@ -3501,11 +3501,7 @@ class B {
     }
     _checkCacheEntries(cache);
 
-    try {
-      assertSameResolution(unit, fullNewUnit);
-    } on IncrementalResolutionMismatch catch (mismatch) {
-      fail(mismatch.message);
-    }
+    assertSameResolution(unit, fullNewUnit);
     // errors
     List<AnalysisError> newFullErrors =
         analysisContext.getErrors(source).errors;
@@ -4849,11 +4845,44 @@ class B extends A {}
     }
   }
 
-  void _assertCacheResults({bool expectCachePostConstantsValid: true}) {
+  void test_updateFunctionToForLoop() {
+    _resolveUnit(r'''
+class PlayDrag {
+  final List<num> times = new List<num>();
+
+  PlayDrag.start() {}
+
+  void update(num pos) {
+    fo (int i = times.length - 2; i >= 0; i--) {}
+  }
+}
+''');
+
+    _updateAndValidate(
+        r'''
+class PlayDrag {
+  final List<num> times = new List<num>();
+
+  PlayDrag.start() {}
+
+  void update(num pos) {
+    for (int i = times.length - 2; i >= 0; i--) {}
+  }
+}
+''',
+        expectLibraryUnchanged: false);
+  }
+
+  void _assertCacheResults(
+      {bool expectLibraryUnchanged: true,
+      bool expectCachePostConstantsValid: true}) {
     _assertCacheSourceResult(TOKEN_STREAM);
     _assertCacheSourceResult(SCAN_ERRORS);
     _assertCacheSourceResult(PARSED_UNIT);
     _assertCacheSourceResult(PARSE_ERRORS);
+    if (!expectLibraryUnchanged) {
+      return;
+    }
     _assertCacheSourceResult(LIBRARY_ELEMENT1);
     _assertCacheSourceResult(LIBRARY_ELEMENT2);
     _assertCacheSourceResult(LIBRARY_ELEMENT3);
@@ -4943,6 +4972,7 @@ class B extends A {}
 
   void _updateAndValidate(String newCode,
       {bool expectedSuccess: true,
+      bool expectLibraryUnchanged: true,
       bool expectCachePostConstantsValid: true,
       bool compareWithFull: true,
       bool runTasksBeforeIncremental: true}) {
@@ -4955,7 +4985,9 @@ class B extends A {}
     _resetWithIncremental(true);
     analysisContext2.setContents(source, newCode);
     CompilationUnit newUnit = resolveCompilationUnit(source, oldLibrary);
-    expect(logger.hasError, isFalse);
+    if (logger.hasError) {
+      fail("logged an error: ${logger.lastError}");
+    }
     List<AnalysisError> newErrors = analysisContext.computeErrors(source);
     LineInfo newLineInfo = analysisContext.getLineInfo(source);
     // check for expected failure
@@ -4966,6 +4998,7 @@ class B extends A {}
     // The cache must still have enough results to make the incremental
     // resolution useful.
     _assertCacheResults(
+        expectLibraryUnchanged: expectLibraryUnchanged,
         expectCachePostConstantsValid: expectCachePostConstantsValid);
     // The existing CompilationUnit[Element] should be updated.
     expect(newUnit, same(oldUnit));
@@ -5255,7 +5288,9 @@ class _Edit {
 }
 
 class _TestLogger implements logging.Logger {
-  bool hasError = false;
+  Object lastError;
+
+  bool get hasError => lastError != null;
 
   @override
   void enter(String name) {}
@@ -5268,7 +5303,7 @@ class _TestLogger implements logging.Logger {
 
   @override
   void logException(Object exception, [Object stackTrace]) {
-    hasError = true;
+    lastError = exception;

[Brian Wilkerson, 2016/02/16 15:10:48]

Seems like it would be useful to also capture the stack trace so that we could
include it in the failure message. Also, perhaps replace `hasError` with an
`expectNoErrors` method that calls `fail` directly because that would ensure
that we're always including the extra debugging information.

[skybrian, 2016/02/17 01:23:41]

Done.

   }
 
   @override