KT-175: infer nullability in then block from if condition

if (x != null) {
    // x is non-null here
}

compiler/frontend/src/org/jetbrains/jet/lang/resolve/calls/CallResolver.java

@@ -652,7 +652,7 @@ public class CallResolver {
             List<JetExpression> argumentExpressions = resolvedArgument.getArgumentExpressions();
             for (JetExpression argumentExpression : argumentExpressions) {
                 ExpressionTypingServices temporaryServices = new ExpressionTypingServices(semanticServices, candidateCall.getTrace());
-                JetType type = temporaryServices.getType(scope, argumentExpression, parameterType);
+                JetType type = temporaryServices.getType(scope, argumentExpression, parameterType, dataFlowInfo);
                 if (type == null) {
                     candidateCall.argumentHasNoType();
                 }

compiler/frontend/src/org/jetbrains/jet/lang/types/expressions/ExpressionTypingServices.java

@@ -53,10 +53,15 @@ public class ExpressionTypingServices {
 
     @Nullable
     public JetType getType(@NotNull final JetScope scope, @NotNull JetExpression expression, @NotNull JetType expectedType) {
+        return getType(scope, expression, expectedType, DataFlowInfo.EMPTY);
+    }
+
+    @Nullable
+    public JetType getType(@NotNull final JetScope scope, @NotNull JetExpression expression, @NotNull JetType expectedType, DataFlowInfo dataFlowInfo) {
         ExpressionTypingContext context = ExpressionTypingContext.newContext(
                 semanticServices,
                 new HashMap<JetPattern, DataFlowInfo>(), new HashMap<JetPattern, List<VariableDescriptor>>(), new LabelResolver(),
-                trace, scope, DataFlowInfo.EMPTY, expectedType, FORBIDDEN, false
+                trace, scope, dataFlowInfo, expectedType, FORBIDDEN, false
         );
         return expressionTypingFacade.getType(expression, context);
     }

compiler/testData/checkerWithErrorTypes/quick/InferNullabilityInThenBlock.jet

@@ -0,0 +1,11 @@
+
+fun ff(a: String) = 1
+
+fun gg() {
+    val a: String? = ""
+
+    if (a != null) {
+        ff(a)
+    }
+}
+