I'd very much want to understand the full intent and scenarios here; if this is resolving down to the real file system, that's probably not ideal.

What problem are we trying to solve, and how does this fix address it?

The intent is to remove the .. from the paths given to the AdditionalFiles.

An example could be e.g.

    <AdditionalFiles Include="../../proto/base.proto" />
    <AdditionalFiles Include="../../proto/interface/rpc.proto" ImportPaths="../" />

These would be added to AdditionalFilesFileSystem as:

• {repo dir}/src/App/../../proto/base.proto
• {repo dir}/src/App/../../proto/interface/rpc.proto

rpc.proto relies on imported definitions from base.proto. An import path has to be added. If I'm not mistaken the generator tries to find base.proto (in the virtual file system) at the same path as rpc.proto. Next, it tries to go through the import paths.

As the example is presented, it will try to look for base.proto at {repo dir}/proto/ which is where it is located. In the look-up logic the path will look like this: {repo dir}/proto/base.proto. When trying to find the path in the virtual file system, it will end up doing this comparison: {repo dir}/src/App/../../proto/base.proto == {repo dir}/proto/base.proto which won't work.