Safety check incorrect for := and with

[tim-styra]

Expected Behavior

Both of the following rules should be safe. They only differ in that one assigns x := and the other assigns x =

package foo
bar {
    q := 1
    x = data.qux with input as q
}

package foo
bar {
    q := 1
    x := data.qux with input as q
}

Actual Behavior

First rule is safe. Second rule is unsafe:

error: compile error: 1 error occurred: t.rego:2: rego_unsafe_var_error: var q is unsafe

Steps to Reproduce the Problem

opa run with either one of the above modules.

Additional Info