Issue 6399. Don't fall back to 'dynamic' when variable has explicit type.

compiler/javatests/com/google/dart/compiler/type/TypeAnalyzerCompilerTest.java

Index: compiler/javatests/com/google/dart/compiler/type/TypeAnalyzerCompilerTest.java
diff --git a/compiler/javatests/com/google/dart/compiler/type/TypeAnalyzerCompilerTest.java b/compiler/javatests/com/google/dart/compiler/type/TypeAnalyzerCompilerTest.java
index 39797f3a86db5fbe87bbd5769e4d6e942db9a6f6..92c941d23c75d4a9478d7919a41cc47f7cda840a 100644
--- a/compiler/javatests/com/google/dart/compiler/type/TypeAnalyzerCompilerTest.java
+++ b/compiler/javatests/com/google/dart/compiler/type/TypeAnalyzerCompilerTest.java
@@ -2409,8 +2409,7 @@ public class TypeAnalyzerCompilerTest extends CompilerTestCase {
   }
 
   /**
-   * When single variable has conflicting type constraints, right now we don't try to unify them,
-   * instead we fall back to "dynamic".
+   * When single variable has conflicting type constraints, we use union of types.
    */
   public void test_typesPropagation_ifIsType_conflictingTypes() throws Exception {
     analyzeLibrary(
@@ -2421,7 +2420,7 @@ public class TypeAnalyzerCompilerTest extends CompilerTestCase {
         "  }",
         "}",
         "");
-    assertInferredElementTypeString(testUnit, "v1", "dynamic");
+    assertInferredElementTypeString(testUnit, "v1", "[int, String]");
   }
 
   public void test_typesPropagation_ifIsType_negation() throws Exception {
@@ -2769,6 +2768,38 @@ public class TypeAnalyzerCompilerTest extends CompilerTestCase {
     assertInferredElementTypeString(testUnit, "b3", "dynamic");
   }
 
+  /**
+   * When variable has explicit type, we should not fall to 'dynamic', we need to keep this type.
+   * <p>
+   * http://code.google.com/p/dart/issues/detail?id=6399
+   */
+  public void test_typesPropagation_assertIsType_hasExplicitType() throws Exception {
+    analyzeLibrary(
+        "class A {}",
+        "class B extends A {}",
+        "class C extends B {}",
+        "main() {",
+        "  B v;",
+        "  if (v is A) {",
+        "    var v1 = v;",
+        "  }",
+        "  if (v is B) {",
+        "    var v2 = v;",
+        "  }",
+        "  if (v is C) {",
+        "    var v3 = v;",
+        "  }",
+        "  if (v is String) {",
+        "    var v4 = v;",
+        "  }",
+        "}",
+        "");
+    assertInferredElementTypeString(testUnit, "v1", "B");
+    assertInferredElementTypeString(testUnit, "v2", "B");
+    assertInferredElementTypeString(testUnit, "v3", "C");
+    assertInferredElementTypeString(testUnit, "v4", "[B, String]");
+  }
+
   public void test_typesPropagation_field_inClass_final() throws Exception {
     analyzeLibrary(
         "// filler filler filler filler filler filler filler filler filler filler",