Weird error when iterating over object

[sparkprime]

$ jsonnet -e '[x for x in {a: "foo"}]'
RUNTIME ERROR: Object index must be string, got double.
                thunk <x>
        <cmdline>:1:2   thunk <array_element>
        During manifestation

[sparkprime]

Probably the code is doing x[i] for i in std.range(0, std.length({a: "foo"})} and length of an object is the number of keys. Best thing to do right now is to put an explicit check in that it's an array and not an object.