Put functional tests in `tests/functional`

I think it is bad for these reasons when `tests/` contains a mix of
functional and integration tests

 - Concepts is harder to understand, the documentation makes a good
   unit vs functional vs integration distinction, but when the
   integration tests are just two subdirs within `tests/` this is not
   clear.

 - Source filtering in the `flake.nix` is more complex. We need to
   filter out some of the dirs from `tests/`, rather than simply pick
   the dirs we want and take all of them. This is a good sign the
   structure of what we are trying to do is not matching the structure
   of the files.

With this change we have a clean:
```shell-session
$ git show 'HEAD:tests'
tree HEAD:tests

functional/
installer/
nixos/
```

(cherry picked from commit 68c81c737571794f7246db53fb4774e94fcf4b7e)

1 files changed, 64 insertions, 0 deletions

diff --git a/tests/functional/tarball.sh b/tests/functional/tarball.sh
new file mode 100644
index 000000000..6e621a28c
--- /dev/null
+++ b/tests/functional/tarball.sh
@@ -0,0 +1,64 @@
+source common.sh
+
+clearStore
+
+rm -rf $TEST_HOME
+
+tarroot=$TEST_ROOT/tarball
+rm -rf $tarroot
+mkdir -p $tarroot
+cp dependencies.nix $tarroot/default.nix
+cp config.nix dependencies.builder*.sh $tarroot/
+touch -d '@1000000000' $tarroot $tarroot/*
+
+hash=$(nix hash path $tarroot)
+
+test_tarball() {
+    local ext="$1"
+    local compressor="$2"
+
+    tarball=$TEST_ROOT/tarball.tar$ext
+    (cd $TEST_ROOT && tar cf - tarball) | $compressor > $tarball
+
+    nix-env -f file://$tarball -qa --out-path | grepQuiet dependencies
+
+    nix-build -o $TEST_ROOT/result file://$tarball
+
+    nix-build -o $TEST_ROOT/result '<foo>' -I foo=file://$tarball
+
+    nix-build -o $TEST_ROOT/result -E "import (fetchTarball file://$tarball)"
+    # Do not re-fetch paths already present
+    nix-build  -o $TEST_ROOT/result -E "import (fetchTarball { url = file:///does-not-exist/must-remain-unused/$tarball; sha256 = \"$hash\"; })"
+
+    nix-build  -o $TEST_ROOT/result -E "import (fetchTree file://$tarball)"
+    nix-build  -o $TEST_ROOT/result -E "import (fetchTree { type = \"tarball\"; url = file://$tarball; })"
+    nix-build  -o $TEST_ROOT/result -E "import (fetchTree { type = \"tarball\"; url = file://$tarball; narHash = \"$hash\"; })"
+    # Do not re-fetch paths already present
+    nix-build  -o $TEST_ROOT/result -E "import (fetchTree { type = \"tarball\"; url = file:///does-not-exist/must-remain-unused/$tarball; narHash = \"$hash\"; })"
+    expectStderr 102 nix-build  -o $TEST_ROOT/result -E "import (fetchTree { type = \"tarball\"; url = file://$tarball; narHash = \"sha256-xdKv2pq/IiwLSnBBJXW8hNowI4MrdZfW+SYqDQs7Tzc=\"; })" | grep 'NAR hash mismatch in input'
+
+    [[ $(nix eval --impure --expr "(fetchTree file://$tarball).lastModified") = 1000000000 ]]
+
+    nix-instantiate --strict --eval -E "!((import (fetchTree { type = \"tarball\"; url = file://$tarball; narHash = \"$hash\"; })) ? submodules)" >&2
+    nix-instantiate --strict --eval -E "!((import (fetchTree { type = \"tarball\"; url = file://$tarball; narHash = \"$hash\"; })) ? submodules)" 2>&1 | grep 'true'
+
+    nix-instantiate --eval -E '1 + 2' -I fnord=file://no-such-tarball.tar$ext
+    nix-instantiate --eval -E 'with <fnord/xyzzy>; 1 + 2' -I fnord=file://no-such-tarball$ext
+    (! nix-instantiate --eval -E '<fnord/xyzzy> 1' -I fnord=file://no-such-tarball$ext)
+
+    nix-instantiate --eval -E '<fnord/config.nix>' -I fnord=file://no-such-tarball$ext -I fnord=.
+
+    # Ensure that the `name` attribute isn’t accepted as that would mess
+    # with the content-addressing
+    (! nix-instantiate --eval -E "fetchTree { type = \"tarball\"; url = file://$tarball; narHash = \"$hash\"; name = \"foo\"; }")
+
+}
+
+test_tarball '' cat
+test_tarball .xz xz
+test_tarball .gz gzip
+
+rm -rf $TEST_ROOT/tmp
+mkdir -p $TEST_ROOT/tmp
+(! TMPDIR=$TEST_ROOT/tmp XDG_RUNTIME_DIR=$TEST_ROOT/tmp nix-env -f file://$(pwd)/bad.tar.xz -qa --out-path)
+(! [ -e $TEST_ROOT/tmp/bad ])