Open
Description
AB#1245899 was a customer-visible regression that occurred because MSBuild used an older copy of System.Collections.Immutable than Roslyn, causing build-time failures in a task that referenced Roslyn.
The policy has been that Roslyn owns the Immutable version and everything should match it, but that was missed this time.
dotnet/roslyn#49336 adds a comment but that's not validation.
We should have validation that runs in an automated way that checks these versions (assembly version is probably sufficient; we can likely differ in prereleases most of the time as long as we all converge to runtime GA at VS GA).
It's not totally clear to @JoeRobich or me where this should go, so the first order of business is figuring that out.