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, 106 insertions, 0 deletions

diff --git a/tests/functional/fetchMercurial.sh b/tests/functional/fetchMercurial.sh
new file mode 100644
index 000000000..e6f8525c6
--- /dev/null
+++ b/tests/functional/fetchMercurial.sh
@@ -0,0 +1,106 @@
+source common.sh
+
+[[ $(type -p hq) ]] || skipTest "Mercurial not installed"
+
+clearStore
+
+# Intentionally not in a canonical form
+# See https://github.com/NixOS/nix/issues/6195
+repo=$TEST_ROOT/./hg
+
+rm -rf $repo ${repo}-tmp $TEST_HOME/.cache/nix
+
+hg init $repo
+echo '[ui]' >> $repo/.hg/hgrc
+echo 'username = Foobar <foobar@example.org>' >> $repo/.hg/hgrc
+
+# Set ui.tweakdefaults to ensure HGPLAIN is being set.
+echo 'tweakdefaults = True' >> $repo/.hg/hgrc
+
+echo utrecht > $repo/hello
+touch $repo/.hgignore
+hg add --cwd $repo hello .hgignore
+hg commit --cwd $repo -m 'Bla1'
+rev1=$(hg log --cwd $repo -r tip --template '{node}')
+
+echo world > $repo/hello
+hg commit --cwd $repo -m 'Bla2'
+rev2=$(hg log --cwd $repo -r tip --template '{node}')
+
+# Fetch an unclean branch.
+echo unclean > $repo/hello
+path=$(nix eval --impure --raw --expr "(builtins.fetchMercurial file://$repo).outPath")
+[[ $(cat $path/hello) = unclean ]]
+hg revert --cwd $repo --all
+
+# Fetch the default branch.
+path=$(nix eval --impure --raw --expr "(builtins.fetchMercurial file://$repo).outPath")
+[[ $(cat $path/hello) = world ]]
+
+# In pure eval mode, fetchGit without a revision should fail.
+[[ $(nix eval --impure --raw --expr "(builtins.readFile (fetchMercurial file://$repo + \"/hello\"))") = world ]]
+(! nix eval --raw --expr "builtins.readFile (fetchMercurial file://$repo + \"/hello\")")
+
+# Fetch using an explicit revision hash.
+path2=$(nix eval --impure --raw --expr "(builtins.fetchMercurial { url = file://$repo; rev = \"$rev2\"; }).outPath")
+[[ $path = $path2 ]]
+
+# In pure eval mode, fetchGit with a revision should succeed.
+[[ $(nix eval --raw --expr "builtins.readFile (fetchMercurial { url = file://$repo; rev = \"$rev2\"; } + \"/hello\")") = world ]]
+
+# Fetch again. This should be cached.
+mv $repo ${repo}-tmp
+path2=$(nix eval --impure --raw --expr "(builtins.fetchMercurial file://$repo).outPath")
+[[ $path = $path2 ]]
+
+[[ $(nix eval --impure --raw --expr "(builtins.fetchMercurial file://$repo).branch") = default ]]
+[[ $(nix eval --impure --expr "(builtins.fetchMercurial file://$repo).revCount") = 1 ]]
+[[ $(nix eval --impure --raw --expr "(builtins.fetchMercurial file://$repo).rev") = $rev2 ]]
+
+# But with TTL 0, it should fail.
+(! nix eval --impure --refresh --expr "builtins.fetchMercurial file://$repo")
+
+# Fetching with a explicit hash should succeed.
+path2=$(nix eval --refresh --raw --expr "(builtins.fetchMercurial { url = file://$repo; rev = \"$rev2\"; }).outPath")
+[[ $path = $path2 ]]
+
+path2=$(nix eval --refresh --raw --expr "(builtins.fetchMercurial { url = file://$repo; rev = \"$rev1\"; }).outPath")
+[[ $(cat $path2/hello) = utrecht ]]
+
+mv ${repo}-tmp $repo
+
+# Using a clean working tree should produce the same result.
+path2=$(nix eval --impure --raw --expr "(builtins.fetchMercurial $repo).outPath")
+[[ $path = $path2 ]]
+
+# Using an unclean tree should yield the tracked but uncommitted changes.
+mkdir $repo/dir1 $repo/dir2
+echo foo > $repo/dir1/foo
+echo bar > $repo/bar
+echo bar > $repo/dir2/bar
+hg add --cwd $repo dir1/foo
+hg rm --cwd $repo hello
+
+path2=$(nix eval --impure --raw --expr "(builtins.fetchMercurial $repo).outPath")
+[ ! -e $path2/hello ]
+[ ! -e $path2/bar ]
+[ ! -e $path2/dir2/bar ]
+[ ! -e $path2/.hg ]
+[[ $(cat $path2/dir1/foo) = foo ]]
+
+[[ $(nix eval --impure --raw --expr "(builtins.fetchMercurial $repo).rev") = 0000000000000000000000000000000000000000 ]]
+
+# ... unless we're using an explicit ref.
+path3=$(nix eval --impure --raw --expr "(builtins.fetchMercurial { url = $repo; rev = \"default\"; }).outPath")
+[[ $path = $path3 ]]
+
+# Committing should not affect the store path.
+hg commit --cwd $repo -m 'Bla3'
+
+path4=$(nix eval --impure --refresh --raw --expr "(builtins.fetchMercurial file://$repo).outPath")
+[[ $path2 = $path4 ]]
+
+echo paris > $repo/hello
+# Passing a `name` argument should be reflected in the output path
+path5=$(nix eval -vvvvv --impure --refresh --raw --expr "(builtins.fetchMercurial { url = \"file://$repo\"; name = \"foo\"; } ).outPath")
+[[ $path5 =~ -foo$ ]]