Avoid excessive file system watches for --server

[chklauser]

Fixes #1468 (dotnet-csharpier --server accidentally installs file system watches for the entire directory.)

We configure the server to run against a temporary, empty directory instead, so that the file system watcher that does get installed only has to watch a single, empty directory.

This also means that the server won't pick up the default appsettings.json files in the working directory. We probably don't want this anyway because these appsettings could be intended for the user's solution, not for csharpier.

Alternative approaches are discussed in #1468

[belav]

Thanks for the thorough explanation of the issue!

I wasn't sure how the file watcher uses the project directory as the content root and had the thought that a possible fix would be to set the working directory of the process to the same directory that the csharpier process exists in.

rider does not set a working directory at all. So if the default behavior of rider is to run the process from the project root that could explain how it ends up as the content root.

vscode does specifically set the project directory as the working directory when starting the process. That was changed in #543 but I'm not exactly sure why it was needed.

I think it's worth checking if setting the working directory to the same directory as the csharpier process solves this problem. It means the issue can be fixed by just updating the extensions. When a file is formatted the path of that file is passed to the server, so I am fairly certain we can get anything we need using that path.

If that doesn't work I'd be inclined have the extensions disable csharpier server on linux for versions without this fix.

[chklauser]

Yes, I can confirm that it is the working directory that gets used as the default content root (checked with strace). So if the extensions would set the process working directory to the same directory as the dotnet-csharpier executable, the file system watches wouldn't be that much of a problem.

I still see a bunch watches for directories in the ~/.cache/csharpier/$version/ directory, .store with different subdirectories for languages and .net versions. Unnecessary work still happens. But at least those directories won't experience massive changes (such as git checkouts) while you are working.

But I ultimately don't have a strong opinion on how exactly the issue gets fixed. I have created an issue #1468 with the problem description above (in case there are going to be multiple PRs).