What does "dot slash dot" (./.) mean in a Nix expression? - nix

Question

Wherever I see flake-compat used, it is a variation of
(import (fetchTarball https://github.com/edolstra/flake-compat/archive/master.tar.gz) {
src = ./.;
}).shellNix
It is obviously a path that refers to the current directory which can be proven with a simple test:
[~/testdir]$ ll .
total 24
drwxr-xr-x 2 toraritte users 4096 Jul 21 21:56 ./
drwx------ 7 toraritte users 20480 Jul 15 23:13 ../
-rw-r--r-- 1 toraritte users 0 Jul 21 21:56 lofa
[~/testdir]$ ll ./.
total 24
drwxr-xr-x 2 toraritte users 4096 Jul 21 21:56 ./
drwx------ 7 toraritte users 20480 Jul 15 23:13 ../
-rw-r--r-- 1 toraritte users 0 Jul 21 21:56 lofa
So why not simply use .?

Answer 1

From 5.2.1 Values section of the Nix manual (emphasis mine):
Paths, e.g., /bin/sh or ./builder.sh. A path must contain at least one
slash to be recognised as such.
For instance, builder.sh is not a
path: it's parsed as an expression that selects the attribute sh from
the variable builder. If the file name is relative, i.e., if it does
not begin with a slash, it is made absolute at parse time relative to
the directory of the Nix expression that contained it. For instance,
if a Nix expression in /foo/bar/bla.nix refers to ../xyzzy/fnord.nix,
the absolute path is /foo/xyzzy/fnord.nix.