See Diagnostic Design-Time Builds.
When you build the solution either in Visual Studio or via the command-line, a trace listener is hooked up to output CPS tracing to the Debug category of the Output Window under the RoslynDev Visual Studio instance. You can use this to diagnose lots of issues, such as failing rules or missing snapshots.
You can increase the verbosity of what is output to the window by changing the verbosity level in ManagedProjectSystemPackage.DebuggingTraceListener.
You can see the active capabilities for a given project, by turning on the DiagnoseCapabilities capability:
<ItemGroup>
<ProjectCapability Include="DiagnoseCapabilities"/>
</ItemGroup>This will add a node in Solution Explorer that will list the current 'active' capabilities:
