Hide inference hints. Fixes #24563.

BUG=
R=jmesserly@google.com

Review URL: https://codereview.chromium.org/1498573002 .

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

@@ -267,6 +267,9 @@ class AnalysisContextImpl implements InternalAnalysisContext {
         (this._options.lint && !options.lint) ||
         this._options.preserveComments != options.preserveComments ||
         this._options.strongMode != options.strongMode ||
+        ((options is AnalysisOptionsImpl)
+            ? this._options.strongModeHints != options.strongModeHints
+            : false) ||
         this._options.enableStrictCallChecks !=
             options.enableStrictCallChecks ||
         this._options.enableGenericMethods != options.enableGenericMethods ||
@@ -290,6 +293,9 @@ class AnalysisContextImpl implements InternalAnalysisContext {
     this._options.lint = options.lint;
     this._options.preserveComments = options.preserveComments;
     this._options.strongMode = options.strongMode;
+    if (options is AnalysisOptionsImpl) {
+      this._options.strongModeHints = options.strongModeHints;
+    }
     if (needsRecompute) {
       for (WorkManager workManager in workManagers) {
         workManager.onAnalysisOptionsChanged();

pkg/analyzer/lib/src/generated/engine.dart

@@ -1170,6 +1170,9 @@ class AnalysisContextImpl implements InternalAnalysisContext {
         (this._options.hint && !options.hint) ||
         this._options.preserveComments != options.preserveComments ||
         this._options.strongMode != options.strongMode ||
+        ((options is AnalysisOptionsImpl)
+            ? this._options.strongModeHints != options.strongModeHints
+            : false) ||
         this._options.enableStrictCallChecks !=
             options.enableStrictCallChecks ||
         this._options.enableSuperMixins != options.enableSuperMixins;
@@ -1206,6 +1209,9 @@ class AnalysisContextImpl implements InternalAnalysisContext {
     this._options.lint = options.lint;
     this._options.preserveComments = options.preserveComments;
     this._options.strongMode = options.strongMode;
+    if (options is AnalysisOptionsImpl) {
+      this._options.strongModeHints = options.strongModeHints;
+    }
     _generateImplicitErrors = options.generateImplicitErrors;
     _generateSdkErrors = options.generateSdkErrors;
     if (needsRecompute) {
@@ -6461,6 +6467,14 @@ class AnalysisOptionsImpl implements AnalysisOptions {
    */
   bool strongMode = false;
 
+  /**
+   * A flag indicating whether strong-mode inference hints should be
+   * used.  This flag is not exposed in the interface, and should be
+   * replaced by something more general.
+   */
+  // TODO(leafp): replace this with something more general
+  bool strongModeHints = false;
+
   /**
    * Initialize a newly created set of analysis options to have their default
    * values.
@@ -6488,6 +6502,9 @@ class AnalysisOptionsImpl implements AnalysisOptions {
     lint = options.lint;
     preserveComments = options.preserveComments;
     strongMode = options.strongMode;
+    if (options is AnalysisOptionsImpl) {
+      strongModeHints = options.strongModeHints;
+    }
   }
 
   /**
@@ -6510,6 +6527,9 @@ class AnalysisOptionsImpl implements AnalysisOptions {
     lint = options.lint;
     preserveComments = options.preserveComments;
     strongMode = options.strongMode;
+    if (options is AnalysisOptionsImpl) {
+      strongModeHints = options.strongModeHints;
+    }
   }
 
   bool get analyzeFunctionBodies {

pkg/analyzer/lib/src/generated/resolver.dart

@@ -5771,6 +5771,11 @@ class InferenceContext {
    */
   final AnalysisErrorListener _errorListener;
 
+  /**
+   * If true, emit hints when types are inferred
+   */
+  final bool _inferenceHints;
+
   /**
    * Type provider, needed for type matching.
    */
@@ -5792,8 +5797,8 @@ class InferenceContext {
    */
   List<DartType> _returnStack = <DartType>[];
 
-  InferenceContext._(
-      this._errorListener, TypeProvider typeProvider, this._typeSystem)
+  InferenceContext._(this._errorListener, TypeProvider typeProvider,
+      this._typeSystem, this._inferenceHints)
       : _typeProvider = typeProvider,
         _rules = new TypeRules(typeProvider);
 
@@ -5837,7 +5842,7 @@ class InferenceContext {
    */
   void recordInference(Expression node, DartType type) {
     StaticInfo info = InferredType.create(_rules, node, type);
-    if (info == null) {
+    if (!_inferenceHints || info == null) {
       return;
     }
     AnalysisError error = info.toAnalysisError();
@@ -10695,8 +10700,13 @@ class ResolverVisitor extends ScopedVisitor {
     }
     this.elementResolver = new ElementResolver(this);
     this.typeSystem = definingLibrary.context.typeSystem;
-    this.inferenceContext =
-        new InferenceContext._(errorListener, typeProvider, typeSystem);
+    bool strongModeHints = false;
+    AnalysisOptions options = definingLibrary.context.analysisOptions;
+    if (options is AnalysisOptionsImpl) {
+      strongModeHints = options.strongModeHints;
+    }
+    this.inferenceContext = new InferenceContext._(
+        errorListener, typeProvider, typeSystem, strongModeHints);
     if (typeAnalyzerFactory == null) {
       this.typeAnalyzer = new StaticTypeAnalyzer(this);
     } else {

pkg/analyzer/test/generated/resolver_test.dart

@@ -12587,6 +12587,18 @@ class StrongModeDownwardsInferenceTest extends ResolverTestCase {
     expect(functionReturnValue(4).staticType, typeProvider.stringType);
   }
 
+  void test_inference_hints() {
+    Source source = addSource(r'''
+      void main () {
+        var x = 3;
+        List<int> l0 = [];
+     }
+   ''');
+    LibraryElement library = resolve2(source);
+    assertNoErrors(source);
+    verify([source]);
+  }
+
   void test_instanceCreation() {
     String code = r'''
       class A<S, T> {
@@ -13819,25 +13831,6 @@ class TypeOverrideManagerTest extends EngineTestCase {
 
 @reflectiveTest
 class TypePropagationTest extends ResolverTestCase {
-  void test_invocation_target_prefixed() {
-    addNamedSource(
-        '/helper.dart',
-        '''
-library helper;
-int max(int x, int y) => 0;
-''');
-    String code = '''
-import 'helper.dart' as helper;
-main() {
-  helper.max(10, 10); // marker
-}''';
-    SimpleIdentifier methodName =
-        _findMarkedIdentifier(code, "(10, 10); // marker");
-    MethodInvocation methodInvoke = methodName.parent;
-    expect(methodInvoke.methodName.staticElement, isNotNull);
-    expect(methodInvoke.methodName.propagatedElement, isNull);
-  }
-
   void fail_mergePropagatedTypesAtJoinPoint_1() {
     // https://code.google.com/p/dart/issues/detail?id=19929
     _assertTypeOfMarkedExpression(
@@ -14657,6 +14650,25 @@ main() {
     }
   }
 
+  void test_invocation_target_prefixed() {
+    addNamedSource(
+        '/helper.dart',
+        '''
+library helper;
+int max(int x, int y) => 0;
+''');
+    String code = '''
+import 'helper.dart' as helper;
+main() {
+  helper.max(10, 10); // marker
+}''';
+    SimpleIdentifier methodName =
+        _findMarkedIdentifier(code, "(10, 10); // marker");
+    MethodInvocation methodInvoke = methodName.parent;
+    expect(methodInvoke.methodName.staticElement, isNotNull);
+    expect(methodInvoke.methodName.propagatedElement, isNull);
+  }
+
   void test_is_conditional() {
     Source source = addSource(r'''
 class A {}

pkg/analyzer/test/src/task/strong/strong_test_helper.dart

@@ -63,6 +63,7 @@ void testChecker(String name, Map<String, String> testFiles) {
     AnalysisEngine.instance.useTaskModel = true;
     var context = AnalysisEngine.instance.createAnalysisContext();
     context.analysisOptions.strongMode = true;
+    context.analysisOptions.strongModeHints = true;
 
     context.sourceFactory = new SourceFactory([
       new MockDartSdk(mockSdkSources, reportMissing: true).resolver,