Roslyn CTP: asynchronously search for `return null;` among all sources of solution.

Roslyn-SearchForReturnNull.cs

// load workspace, i.e. solution from Visual Studio
using(var workspace = Workspace.LoadSolution(solutionPath))
{
	// save a reference to original state
	var origianlSolution = workspace.CurrentSolution;
		
	// build syntax root and semantic model asynchronously in parallel 
	// for all documents from all projects 
	returnNulls =
			origianlSolution
				.Projects
				.AsParallel()
					.AsUnordered()
				.WithCancellation(cancellationToken)
				.SelectMany(project => project.Documents)
				.Select(document => document.GetSyntaxRootAsync(cancellationToken))
				// calculate complexity for all methods in parallel
				.SelectMany(syntaxRootAsync => 
							FindReturnNull(syntaxRootAsync, cancellationToken).Result)
				.ToArray();
		
	// throw an exception if more then 1 minute passed since start
	cancellationToken.ThrowIfCancellationRequested();
}

// statements for `return null;`
private static readonly Func<StatementSyntax, bool> returnNullStatement =
        PredicateBuilder
  			.True<StatementSyntax>()
        		.And(s => s is ReturnStatementSyntax)
			.And(s => (s as ReturnStatementSyntax).Expression != null)
			.And(s => (s as ReturnStatementSyntax).Expression.Kind == SyntaxKind.NullLiteralExpression)
                .Compile();

// process descendant nodes of syntaxRoot
private static async Task<IEnumerable<ReturnNull>> FindReturnNull(
                            Task<CommonSyntaxNode> syntaxRootAsync,
                            CancellationToken cancellationToken)
{
    return
        (await syntaxRootAsync)
        	.DescendantNodes()
        	.OfType<ReturnStatementSyntax>()
		.Where(returnNull => returnNullStatement(returnNull))
        	.Select(returnNull =>
                        new ReturnNull
                        {
                        	TypeIdentifier = GetParentSyntax<TypeDeclarationSyntax>(returnNull).Identifier.ValueText,
				SourcesSample = returnNull.ToString(),
				FilePath = returnNull.GetLocation().SourceTree.FilePath,
				SourceLine = returnNull
        					.GetLocation().SourceTree
        					.GetLineSpan(returnNull.Span, true, cancellationToken)
        						.StartLinePosition.Line + 1
                        });
}

Full sample is at github