mango: fix validation of use_index

The `binary:split/2` function will split the input only at the
first occurrence of the pattern which is not suitable for
identifying each part of the index name, therefore validating it.
Add the `global` option to fully break the index name into parts
and let the related validation logic work as expected.

src/mango/src/mango_error.erl

@@ -253,6 +253,12 @@ info(mango_opts, {invalid_bulk_docs, Val}) ->
             [Val]
         )
     };
+info(mango_opts, {invalid_index_name, Val}) ->
+    {
+        400,
+        <<"invalid_index_name">>,
+        fmt("Invalid index name: ~w", [Val])
+    };
 info(mango_opts, {invalid_ejson, Val}) ->
     {
         400,

src/mango/src/mango_opts.erl

@@ -262,7 +262,7 @@ validate_bulk_docs(Else) ->
     ?MANGO_ERROR({invalid_bulk_docs, Else}).
 
 validate_use_index(IndexName) when is_binary(IndexName) ->
-    case binary:split(IndexName, <<"/">>) of
+    case binary:split(IndexName, <<"/">>, [global]) of
         [DesignId] ->
             {ok, [DesignId]};
         [<<"_design">>, DesignId] ->

src/mango/test/05-index-selection-test.py

@@ -211,6 +211,16 @@ def test_explain_sort_reverse(self):
         )
         self.assertEqual(resp_explain["index"]["type"], "json")
 
+    def test_use_index_with_invalid_name(self):
+        for index in ["foo/bar/baz", ["foo", "bar", "baz"]]:
+            with self.subTest(index=index):
+                try:
+                    self.db.find({"manager": True}, use_index=index)
+                except Exception as e:
+                    self.assertEqual(e.response.status_code, 400)
+                else:
+                    raise AssertionError("did not fail on invalid index name")
+
     def test_use_index_without_fallback(self):
         with self.subTest(use_index="valid"):
             docs = self.db.find(