Improve propagation in binary expressions

pkg/analyzer/test/generated/resolver_test.dart

Index: pkg/analyzer/test/generated/resolver_test.dart
diff --git a/pkg/analyzer/test/generated/resolver_test.dart b/pkg/analyzer/test/generated/resolver_test.dart
index e07053da689a29c39eb0d6bb72d028d2f4538a55..da0245a7b677ffbb3fbd1c7b7976dc617c7404c9 100644
--- a/pkg/analyzer/test/generated/resolver_test.dart
+++ b/pkg/analyzer/test/generated/resolver_test.dart
@@ -10111,6 +10111,17 @@ class StaticTypeAnalyzerTest extends EngineTestCase {
     _listener.assertNoErrors();
   }
 
+  void test_visitBinaryExpression_minusID_propagated() {
+    // a - b
+    BinaryExpression node = AstFactory.binaryExpression(
+        _propagatedVariable(_typeProvider.intType, 'a'), TokenType.MINUS,
+        _propagatedVariable(_typeProvider.doubleType, 'b'));
+    node.propagatedElement = getMethod(_typeProvider.numType, "+");
+    _analyze(node);
+    expect(node.propagatedType, same(_typeProvider.doubleType));
+    _listener.assertNoErrors();
+  }
+
   void test_visitBinaryExpression_notEquals() {
     // 2 != 3
     Expression node = AstFactory.binaryExpression(
@@ -10137,6 +10148,17 @@ class StaticTypeAnalyzerTest extends EngineTestCase {
     _listener.assertNoErrors();
   }
 
+  void test_visitBinaryExpression_plusII_propagated() {
+    // a + b
+    BinaryExpression node = AstFactory.binaryExpression(
+        _propagatedVariable(_typeProvider.intType, 'a'), TokenType.PLUS,
+        _propagatedVariable(_typeProvider.intType, 'b'));
+    node.propagatedElement = getMethod(_typeProvider.numType, "+");
+    _analyze(node);
+    expect(node.propagatedType, same(_typeProvider.intType));
+    _listener.assertNoErrors();
+  }
+
   void test_visitBinaryExpression_slash() {
     // 2 / 2
     BinaryExpression node = AstFactory.binaryExpression(
@@ -11104,6 +11126,25 @@ class StaticTypeAnalyzerTest extends EngineTestCase {
       StaticTypeAnalyzer.flattenFutures(_typeProvider, type);
 
   /**
+   * Return a simple identifier that has been resolved to a variable element with the given type.
+   *
+   * @param type the type of the variable being represented
+   * @param variableName the name of the variable
+   * @return a simple identifier that has been resolved to a variable element with the given type
+   */
+  SimpleIdentifier _propagatedVariable(
+      InterfaceType type, String variableName) {
+    SimpleIdentifier identifier = AstFactory.identifier3(variableName);
+    VariableElementImpl element =
+        ElementFactory.localVariableElement(identifier);
+    element.type = type;
+    identifier.staticType = _typeProvider.dynamicType;
+    identifier.propagatedElement = element;
+    identifier.propagatedType = type;
+    return identifier;
+  }
+
+  /**
    * Return an integer literal that has been resolved to the correct type.
    *
    * @param value the value of the literal