path: flake reference has some weird behavior

[bryanhonof]

Describe the bug

When using the path: flake reference to point to flakes inside a git repo, it has some odd behavior.

Steps To Reproduce

$ pushd "$(mktemp -d)"
/var/folders/vw/ksgd_r_j51704dss486tzpmc0000gn/T/tmp.aMK4pdtqNS ~
$ git init
Initialized empty Git repository in /private/var/folders/vw/ksgd_r_j51704dss486tzpmc0000gn/T/tmp.aMK4pdtqNS/.git/
$ nix flake init
wrote: /private/var/folders/vw/ksgd_r_j51704dss486tzpmc0000gn/T/tmp.aMK4pdtqNS/flake.nix
$ nix build path:.
error (ignored): error: end of string reached
error:
       … while fetching the input 'path:.'

       error: file '/private/var/folders/vw/ksgd_r_j51704dss486tzpmc0000gn/T/tmp.aMK4pdtqNS/.git/fsmonitor--daemon.ipc' has an unsupported type
$ # Or
$ nix build path:$PWD
error (ignored): error: end of string reached
error:
       … while fetching the input 'path:/var/folders/vw/ksgd_r_j51704dss486tzpmc0000gn/T/tmp.aMK4pdtqNS'

       error: path '/var' is a symlink
$ nix build "path:$PWD/"
error (ignored): error: end of string reached
error:
       … while fetching the input 'path:/var/folders/vw/ksgd_r_j51704dss486tzpmc0000gn/T/tmp.aMK4pdtqNS/'

       error: path '/var' is a symlink
$ nix build "path:$(realpath $PWD)/"
error (ignored): error: end of string reached
error:
       … while fetching the input 'path:/private/var/folders/vw/ksgd_r_j51704dss486tzpmc0000gn/T/tmp.aMK4pdtqNS/'

       error: file '/private/var/folders/vw/ksgd_r_j51704dss486tzpmc0000gn/T/tmp.aMK4pdtqNS/.git/fsmonitor--daemon.ipc' has an unsupported type

Expected behavior

I would expect Nix to ignore paths that it can't read, or understand, instead of throwing an error.

nix-env --version output

$ nix-env --version
nix-env (Nix) 2.24.6

Additional context

I'm trying to use path: to get around the whole git+file: using HEAD as ref by default.
I'd like to not have to git add . every time I want to evaluate my flake when I'm iterating over it, hence trying to use path:.

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