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, 43 insertions, 0 deletions

diff --git a/tests/functional/eval.sh b/tests/functional/eval.sh
new file mode 100644
index 000000000..b81bb1e2c
--- /dev/null
+++ b/tests/functional/eval.sh
@@ -0,0 +1,43 @@
+source common.sh
+
+clearStore
+
+testStdinHeredoc=$(nix eval -f - <<EOF
+{
+  bar = 3 + 1;
+  foo = 2 + 2;
+}
+EOF
+)
+[[ $testStdinHeredoc == '{ bar = 4; foo = 4; }' ]]
+
+nix eval --expr 'assert 1 + 2 == 3; true'
+
+[[ $(nix eval int -f "./eval.nix") == 123 ]]
+[[ $(nix eval str -f "./eval.nix") == '"foo"' ]]
+[[ $(nix eval str --raw -f "./eval.nix") == 'foo' ]]
+[[ "$(nix eval attr -f "./eval.nix")" == '{ foo = "bar"; }' ]]
+[[ $(nix eval attr --json -f "./eval.nix") == '{"foo":"bar"}' ]]
+[[ $(nix eval int -f - < "./eval.nix") == 123 ]]
+[[ "$(nix eval --expr '{"assert"=1;bar=2;}')" == '{ "assert" = 1; bar = 2; }' ]]
+
+# Check if toFile can be utilized during restricted eval
+[[ $(nix eval --restrict-eval --expr 'import (builtins.toFile "source" "42")') == 42 ]]
+
+nix-instantiate --eval -E 'assert 1 + 2 == 3; true'
+[[ $(nix-instantiate -A int --eval "./eval.nix") == 123 ]]
+[[ $(nix-instantiate -A str --eval "./eval.nix") == '"foo"' ]]
+[[ "$(nix-instantiate -A attr --eval "./eval.nix")" == '{ foo = "bar"; }' ]]
+[[ $(nix-instantiate -A attr --eval --json "./eval.nix") == '{"foo":"bar"}' ]]
+[[ $(nix-instantiate -A int --eval - < "./eval.nix") == 123 ]]
+[[ "$(nix-instantiate --eval -E '{"assert"=1;bar=2;}')" == '{ "assert" = 1; bar = 2; }' ]]
+
+# Check that symlink cycles don't cause a hang.
+ln -sfn cycle.nix $TEST_ROOT/cycle.nix
+(! nix eval --file $TEST_ROOT/cycle.nix)
+
+# Check that relative symlinks are resolved correctly.
+mkdir -p $TEST_ROOT/xyzzy $TEST_ROOT/foo
+ln -sfn ../xyzzy $TEST_ROOT/foo/bar
+printf 123 > $TEST_ROOT/xyzzy/default.nix
+[[ $(nix eval --impure --expr "import $TEST_ROOT/foo/bar") = 123 ]]