I'm trying to have Code Analysis going for my .NET Standard 2.0 class library. As described here, I've added a reference to Microsoft.CodeAnalysis.FxCopAnalyzers. At the beginning, everything looked good and I started getting CA* warnings when building the project. However, after a while, these warnings disappeared although I hadn't touched the code.
Only after closing VS 2017, deleting all bin directories, restarting VS 2017, I started getting back the CA* warnings. However, this doesn't seem to be the recipe to get them back: in my CI environment, the same thing happened. I lost the warnings after an unrelated commit and I still didn't manage to bring them back although I've cleaned the checkout directory completely.
I wonder what could be the reason that at moments the Code Analysis stops working. Unfortunately, I haven't figured out a way to reproduce this - thus my question.
As a matter of fact, I'm eager to understand why adding a NuGet to a project can modify the outcome of the compilation process at all. How does that magic work? Any pointers are welcome.
The new C# and VB compilers are based on Roslyn. Roslyn is an extensible compiler framework where a number of analyzers can run at different stages of the compilation process.
MsBuild will pass the analyzers references from the project file to the call to the Roslyn compiler, which will load these in turn and will execute them after the sources have been parsed and interpreted.
The NuGet packages have special metadata that ensures that these analyzers are added as a special type of reference to the MsBuild project file so that MsBuild can pass these along to the compiler.
This is hard to say. Some metadata of projects is stored. Setting the options to clear the workspace/working directory and start afresh may fix this. Setting the build.clean variable to all should help with that. Deleting the bin, obj and .vs folder as well as the packages folder and performing a nuget restore + build should bring you back into a usable state.
The new FxCop analyzer project still isn't complete and is still being updated. A bug in the analyzer infrastructure can cause the analysis to fail. Unfortunately, this is generally very hard to debug. Turning off rules one by one may help you find the culprit.
There seems to be an option built into Roslyn to enable ETW Logging, which should give you a lot more details, but this isn't very well documented.
In Visual Studio there is another thing that can break the analyzers, Visual Studio Extensions can load analyzers as well, which Visual Studio will then inject into the build process. These extensions are not part of your project and thus won't show up in source control in any way. Any recently updated extension could thus also be the culprit. Setting the MsBuild verbosity level to Diagnostics should show you which analyzers are passed to csc, which should help you figure out where your problem may be coming from.