Add some tests for the CLI completion

tests/completions.sh

@@ -0,0 +1,48 @@
+source common.sh
+
+cd "$TEST_ROOT"
+
+mkdir -p dep && pushd dep
+cat <<EOF > flake.nix
+{
+    outputs = i: { };
+}
+EOF
+popd
+mkdir -p foo && pushd foo
+cat <<EOF > flake.nix
+{
+    inputs.a.url = "path:$(realpath ../dep)";
+
+    outputs = i: {
+        sampleOutput = 1;
+    };
+}
+EOF
+
+popd
+
+# Test the completion of a subcommand
+[[ $(printf "normal\nbuild\t\n") == $(NIX_GET_COMPLETIONS=1 nix buil) ]]
+[[ $(printf "normal\nmetadata\t\n") == $(NIX_GET_COMPLETIONS=2 nix flake metad) ]]
+
+# Filename completion
+[[ $(printf "filenames\n./foo\t\n") == $(NIX_GET_COMPLETIONS=2 nix build ./f) ]]
+[[ $(printf "filenames\n") == $(NIX_GET_COMPLETIONS=2 nix build ./nonexistent) ]]
+
+# Input override completion
+[[ $(printf "normal\na\t\n") == $(NIX_GET_COMPLETIONS=4 nix build ./foo --override-input '') ]]
+
+# Cli flag completion
+NIX_GET_COMPLETIONS=2 nix build --log-form | grep -- "--log-format"
+
+# Config option completion
+## With `--option`
+NIX_GET_COMPLETIONS=3 nix build --option allow-import-from | grep -- "allow-import-from-derivation"
+## As a cli flag – not working atm
+# NIX_GET_COMPLETIONS=2 nix build --allow-import-from | grep -- "allow-import-from-derivation"
+
+
+# Attr path completions
+[[ $(printf "attrs\n./foo#sampleOutput\t\n") == $(NIX_GET_COMPLETIONS=2 nix eval ./foo\#sam) ]]
+[[ $(printf "attrs\noutputs\t\n") == $(NIX_GET_COMPLETIONS=4 nix eval --file ./foo/flake.nix outp) ]]

tests/local.mk

@@ -102,6 +102,7 @@ nix_tests = \
   suggestions.sh \
   store-ping.sh \
   fetchClosure.sh \
+  completion.sh \
   impure-derivations.sh
 
 ifeq ($(HAVE_LIBCPUID), 1)