Type checker fails to identify type from reference

[anderseknert]

No error reported

package p

a := "foo"
s := sum([1, a])

This should fail as sum only accepts numeric values. However, it doesn't. When the value is used directly, the type checker correctly reports the error.

Error reported

package p

s := sum([1, "foo"])

Playground

Could be that there are more examples where the type isn't correctly inferred — I haven't looked into that. This was just something that I hit when working on Regal this evening.

[anderseknert]

Updated title as this also passes the type checker, so it's not just rule references that aren't identified:

allow := s if {
    a := "foo"
    s := sum([1, a])
}

[anderseknert]

While I haven’t done a proper bisect, testing this out with some OPA binaries I had laying around, this bug is at least not a recent regression.

OPA v0.17.0(!!) correctly identifies this as a type error, but not OPA v0.30.0 or anything later I ran with. I did not test any version between those two, but I don't think it matters much. I'm surprised this hasn't been reported in all this time though! Fixing it would be great, as I'm sure those new to Rego and all the built-in functions are going to spend even more time than I did trying to understand what they did wrong.