As others have noted, Microsoft hasn't prioritized Code Contracts and its long-term support remains unclear (though there has been some ongoing discussion about language-level integration via Roslyn).
As of March 11th, 2017, however, community contributor Yaakov has, at least, updated the source code to include the Visual Studio 2017 build targets (thank you!). This version provides support for both static checking during compilation, as well as run-time validation using CCRewrite.
Note: This build does not provide configuration support via the project's properties pane. As such, code contracts will need to be configured by manually adding the appropriate properties to the csproj file. See @crimbo's answer below for a comprehensive list of properties.
Unfortunately, while these updates have been merged into the master code branch, they are neither reflected in Marketplace distribution or the official NuGet Package. As such, you need to download and compile the source code from the repository (which is easy; just use the supplied BuildCC.bat file).
Important: The static analysis for Code Contracts has a hard-coded dependency on .NET 3.5, which is no longer installed by default in either Windows 10 or Visual Studio 2017. As such, you'll want to ensure this "feature" is enabled (or download it separately); otherwise, you'll get a compile-time error.
Alternatively, as of June 15th, 2017—and later updated on February 6th, 2018—contributor Igor Bek has included this update in his NuGet Package, so the simplest approach is to just add CodeContracts.MSBuild to your packages.config via:
Install-Package CodeContracts.MSBuild -Version 1.12.0
Background: Igor Bek first put this package together as a proof-of-concept for the Code Contracts team, and it was later the basis for the official NuGet package (in v1.10.10126.2). Since Microsoft hasn't updated the official NuGet package, his is now the most up-to-date.
Given the current state of support, I wouldn't encourage people to adopt Code Contracts for new projects, but this should provide backward compatibility for developers who have already invested into Code Contracts for existing .NET Framework projects.
