Inconsistent copy of transitive assembly references with FastUpToDate build about project-system HOT 4 OPEN

@drewnoakes for investigation

from project-system.

@govert thank you for the detailed repro. That's very helpful. We will take a look asap.

In ClassLibrary1.csproj, add an assembly reference to the output of ClassLibrary2. This adds a Reference item with its HintPath.

Why use a Reference instead of a ProjectReference? Referencing the output of another project in this way is not supported. For one thing, it hides the build order dependency from the build system. It's possible that the bug here is just a race condition.

from project-system.

In our actual case, we were just referencing an external library (for which we did not have a project, solution or NuGet package) on its own. But when writing up the repro, I tried picking some random assembly from a NuGet package, but that was harder to explain in the write-up than just to add another project and use its output.
The point is not that the extra reference is from a project that is part of the solution, or how it is built. It's just an assembly that is outside the solution and projects and pulled in as a <Reference> item with a HintPath (not sure that's important) into a ProjectReferenced library project. Then the FUTD build transitively copies the extra assembly, inconsistent with a normal build.

(An extra quirk in our case was that the assembly .dll file had been renamed, so the internal assembly name did not match the .dll file name. But that seemed incidental too, and not needed to reproduce the extra copy.)

from project-system.

I tried it now and referencing a library from a NuGet package in the C:\Users\<User>\.NuGet\Packages cache, or another faraway location, does not cause the copy under FUTD build. Then copying that same library to a directory under the solution directory does causes the FUTD problem again. So, the location relative to the solution file (or ConsoleApp project ?) seems important, but nothing about the assembly itself.

from project-system.