Impicit return type is not checked in readonly-array

[jonaskello]

if the function has return [1, 2, 3] without explicit return type that needs to be checked too.

[jonaskello]

Turns out this is quite hard to detect. It is easy in this case:

return [1, 2, 3];

But it gets harder if you have a return statement like this:

return [1, 2, 3] === [1, 2, 3];

To detect it properly we probably need to have full type-checking but that will slow down performance. Perhaps it is better to skip implicit return type checking and instead recommend that the this built-in rule is enabled:

"typedef": [true, "call-signature"]

That will ensure that all functions have an explicit return type and will avoid the problem of returning mutable things implicitly.