Issue 20144. Reset propagated type if one of the 'if' branches changes it to a different one.

pkg/analyzer/test/generated/resolver_test.dart

 // Copyright (c) 2014, 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 engine.resolver_test;
 
 import 'dart:collection';
 
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/element.dart';
@@ skipping 12731 matching lines @@
     ReturnStatement statement = body.block.statements[1] as ReturnStatement;
     SimpleIdentifier identifier = statement.expression as SimpleIdentifier;
     InterfaceType propagatedType = identifier.propagatedType as InterfaceType;
     expect(propagatedType.element, same(typeProvider.mapType.element));
     List<DartType> typeArguments = propagatedType.typeArguments;
     expect(typeArguments, hasLength(2));
     expect(typeArguments[0], same(typeProvider.dynamicType));
     expect(typeArguments[1], same(typeProvider.dynamicType));
   }
 
+  void test_mergePropagatedTypes_afterIfThen_different() {
+    _assertTypeOfMarkedExpression(r'''
+main() {
+  var v = 0;
+  if (v != null) {
+    v = '';
+  }
+  return v; // marker
+}''', null, null);
+  }
+
+  void test_mergePropagatedTypes_afterIfThen_same() {
+    _assertTypeOfMarkedExpression(r'''
+main() {
+  var v = 1;
+  if (v != null) {
+    v = 2;
+  }
+  return v; // marker
+}''', null, typeProvider.intType);
+  }
+
+  void test_mergePropagatedTypes_afterIfThenElse_different() {
+    _assertTypeOfMarkedExpression(r'''
+main() {
+  var v = 1;
+  if (v != null) {
+    v = 2;
+  } else {
+    v = '3';
+  }
+  return v; // marker
+}''', null, null);
+  }
+
+  void test_mergePropagatedTypes_afterIfThenElse_same() {
+    _assertTypeOfMarkedExpression(r'''
+main() {
+  var v = 1;
+  if (v != null) {
+    v = 2;
+  } else {
+    v = 3;
+  }
+  return v; // marker
+}''', null, typeProvider.intType);
+  }
+
   void test_mergePropagatedTypesAtJoinPoint_4() {
     // https://code.google.com/p/dart/issues/detail?id=19929
     _assertTypeOfMarkedExpression(r'''
 f5(x) {
   var y = [];
   if (x) {
     y = 0;
   } else {
     return y;
   }
@@ skipping 238 matching lines @@
    * @param expectedStaticType if non-null, check actual static type is equal to this.
    * @param expectedPropagatedType if non-null, check actual static type is equal to this.
    * @throws Exception
    */
   void _assertTypeOfMarkedExpression(String code, DartType expectedStaticType,
       DartType expectedPropagatedType) {
     SimpleIdentifier identifier = _findMarkedIdentifier(code, "; // marker");
     if (expectedStaticType != null) {
       expect(identifier.staticType, expectedStaticType);
     }
-    if (expectedPropagatedType != null) {
-      expect(identifier.propagatedType, expectedPropagatedType);
-    }
+    expect(identifier.propagatedType, expectedPropagatedType);
   }
 
   /**
    * Return the `SimpleIdentifier` marked by `marker`. The source code must have no
    * errors and be verifiable.
    *
    * @param code source code to analyze.
    * @param marker marker identifying sought after expression in source code.
    * @return expression marked by the marker.
    * @throws Exception
@@ skipping 665 matching lines @@
         // check propagated type
         FunctionType propagatedType = node.propagatedType as FunctionType;
         expect(propagatedType.returnType, test.typeProvider.stringType);
       } on AnalysisException catch (e, stackTrace) {
         thrownException[0] = new CaughtException(e, stackTrace);
       }
     }
     return null;
   }
 }