GetFileDependsOnNETStandard holds handles to assemblies after it returns

I believe this is the root cause of https://github.com/NuGet/Home/issues/5609.

I’ve been looking at this with @mishra14.

It appears that GetFileDependsOnNETStandard, introduced to support .NET Standard 2.0 in VS 15.3, holds locks on files longer than it should.

It appears to close the handle to the files it’s inspecting, but we can observe through the debugger that they don’t get closed immediately–stepping over that line and running a handle.exe search shows the handle still open.

When devenv.exe is started from an environment with set ImplicitlyExpandNETStandardFacades=false, project creation succeeds. That property disables calling GetDependsOnNETStandard.

[ericstj]

I see. I suspect we’re missing this: https://github.com/Microsoft/msbuild/blob/cc5661488dba7c2a25ad1555fee08a9237a2414b/src/Tasks/AssemblyDependency/AssemblyInformation.cs#L500-L503

So in the finally block add:

if (assemblyImport != null)
{
    Marshal.ReleaseComObject(assemblyImport);
}
if (metadataDispenser != null)
{
    Marshal.ReleaseComObject(metadataDispenser);
}

[livarcocc]

I see that @ericstj has fixed this issue already. As such I am going to close it. If that’s not the case, just comment and we can re-activate.