Nix path&git behavior

test.nix

#!/usr/bin/env bash

set -euo pipefail
set -x

rm -rf A B
mkdir -p A B

pushd A
echo foo > foo
cat <<EOF > flake.nix
{ outputs = { self }: { foo = builtins.readFile "\${self}/foo"; }; }
EOF
git init
git add flake.nix
popd

pushd B
cat <<EOF > flake.nix
{
  inputs.A.url = "$(realpath ../A)";

  outputs = { self, A }: {
    foo = A.foo;
  };
}
EOF
popd

# A#foo evaluatis iff A is taken as a `path:` input and not a `git+file:`input
nix eval "path:$(realpath A)"\#foo
( ! nix eval "git+file:$(realpath A)"\#foo )

# Cli arguments resolve a plain path pointing to a git repo to git+file
(! nix eval ./A\#foo)
# Same for flake inputs
(! nix eval ./B\#foo)
# builtins.getFlake don’t
nix eval --impure --expr '(builtins.getFlake "'$(realpath A)'").foo'
# Neither do the registry
nix registry add A "$(realpath A)" --option flake-registry "$PWD/registry.json"
nix eval ./B\#foo --option flake-registry "$PWD/registry.json" --override-input A A