Code Contracts in Visual Studio 2017

At the moment, the Code Contracts project has not caught up to Visual Studio 2017. As a work-around, you can copy a file from the install for Visual Studio 2015 into the proper place and it will allow the projects to build. It will not, however, enable the tab for setting the options in the Project Properties. For that you will still need to open the project in Visual Studio 2015.

The word Community will need to be replaced by the specific version of Visual Studio you have installed, Community, Professional, etc., in the script that follows.

This can be placed into a batch file (fixcontracts.bat) that can be checked into the project. Run the batch file as an administrator.

xcopy /y "C:\Program Files (x86)\MSBuild\14.0\Microsoft.Common.Targets\ImportAfter\CodeContractsAfter.targets" "C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\MSBuild\15.0\Microsoft.Common.targets\ImportAfter\"
setx /m TargetFrameworkSDKToolsDirectory "C:\Program Files (x86)\Microsoft SDKs\Windows\v10.0A\bin\NETFX 4.7 Tools\\"
pause

The line with TargetFrameworkSDKToolsDirectory sets a system environment variable to point to a directory where it can find sn.exe that re-signs the executable after adding the contracts. The defaults inside the targets file do not find sn.exe correctly (at least in some of my environments) without this variable. The two slashes at the end are not a mistake; the first escapes the second and only seems to be needed when preceding a quote mark. If you need to adjust this variable later, you can type System in the taskbar search box, then click the  Advanced system settings item, then click the Environment Variables button and edit it in the dialog that appears.
Contracts won't work with the .Net Framework 4.7, at least until they do a new release, so stick with 4.6 at the latest.