Index signature schema key type with union of literals not evaluated

[diefans]

Bug Report

I want to constrain the keys of an index schema against a type alias (union with literals). Using this type for values works as expected, but using this type to constrain the key of index signature schemas does not work.

I know that I can create a "check" in the schema to validate against a set of strings, but then the question arises, how to constrain the check against the type _foo without duplicating the definition of _foo.

I also played with other types for the key e.g. int and kcl throws an error ("invalid index signature key type: 'int'"), which suggests that only strings are allowed, but that would make specifying a type for the key obsolete at all...

1. Minimal reproduce step (Required)

type _foo = "foo" | "bar"

schema IndexSignature:
    [..._foo]: any

IndexSignature {
    foo = "foo"
    # this should throw an error
    baz: "baz"
}

2. What did you expect to see? (Required)

something like ^ expected str(foo) | str(bar), got str(baz)

3. What did you see instead (Required)

foo: foo
baz: baz

4. What is your KCL components version? (Required)

0.11.0-linux-amd64