Rule: use-object-keys

[anderseknert]

Another rule in the "let's use a built-in for that" series. Whenever a set comprehension is used to collect the keys from an object, we should recommend using object.keys instead, as it's easier to read, and less "imperative".

Avoid

package policy

keys := {k | some k, _ in input.object}

# or

keys := {k | some k; input.object[k]}

Prefer

package policy

keys := object.keys(input.object)

Most often, we can't really tell the type of the input used in a comprehension like this statically. Meaning that something like:

{user | some user, _ in users}

...could be collecting indices of an array, or "key" values from a set. However, collecting array indices into a set seems unlikely / pointless, and collecting values from a set into another set with no further processing is equally pointless. Obviously, we'll need to ensure that only the simples form matches, not when more things happen in the comprehension.