When using RX 2 Contract Assemblies from the RXX project, Static Analyzer doesn't seem to understand contracts on the observable creation methods

Question

When I use methods such as:

IObservable<T> Observable.Create<T>(Func<IObserver<T>,IDisposable>);
IObservable<T> Observable.Defer<T>(Func<IObservable<T>);
IObservable<T2> Observable.Using<T1,T2>(Func<T1>,Func<T1,IObserver<T2>,IObservable<T2>>)

The Analyzer cannot prove that their return value is not NULL, even though in the contract assembly they have a contract.Ensures on them:

public static IObservable<TValue> Defer<TValue>(Func<IObservable<TValue>> observableFactory)
{
Contract.Requires(observableFactory != null, null, "observableFactory != null");
Contract.Ensures(Contract.Result<IObservable<TValue>>() != null, null, "Contract.Result<IObservable<TValue>>() != null");
return null;
}

Here are some examples:

"ensures unproven: Contract.Result<IObservable<object>>() != null"

        private IObservable<object> ExecuteObservableService<TRequestDto, TResponseDto>(TRequestDto request)
            where TResponseDto : class, IObservable<object>
            where TRequestDto : class
        {
            Contract.Requires(request != null);
            Contract.Ensures(Contract.Result<IObservable<object>>() != null);

            return Observable.Using(_serviceFactory.GetService<TRequestDto, TResponseDto>, service => service.Instance.Execute(request));
        }

"ensures unproven: Contract.Result<IObservable<ProjectorResult>>() != null"

        /// <inheritdoc/>
        public IObservable<ProjectorResult> Project(IProjector[] projectors, Func<long, IObservable<Commit>> queryCommits)
        {
            return Observable.Create<ProjectorResult>(observer => ProjectionistObservable(observer, projectors, queryCommits));
        }

"requires unproven: source != null" (it is complaining about the "Requires" rule for the .Where operator)

            return Observable
                .Defer(async () => _zookeeperClient.WatchData(await GetJobPathAsync(request.WorkflowId, request.JobId).NoContext()))
                .Where(data => data != null && data.Count() >= 8)

The last example proves that the analyzer is using the contract assembly (since it is complaining about a Requires within the Where method.

Any ideas how to fix this?

Answer 1

Hi,

I've run into the same problem as well.  It's one of the reasons that I never published the contract assemblies for Rx 2.0 as a separate download.

I assume the issue has something to do with the fact that I created the contract assemblies by hand.  There must be some subtle difference between these assemblies and contract assemblies that are generated by the CC tools.  The contract assemblies that I had created for Rx 1.0 worked fine.  I combed over the new contract assemblies carefully, comparing them to existing contract assemblies that ship with CC, but I couldn't find any obvious differences.  I tried several small adjustments to match the attributes in FCL contract assemblies, but nothing has worked.

The issue may go away once I add the contracts directly to the Rx library and let CC generate contract assemblies from the source, but it's only a work-in-progress:

http://rx.codeplex.com/SourceControl/network/forks/davedev/RxCodeContracts

Note that I've actually made some progress already, I just haven't checked it in yet.

- Dave

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http://davesexton.com/blog