implementation's when clause treats unknowns as true

[sanderr]

The when clause for an implementation treats Unknown values as if they were true, i.e. it emits the implementation. This is not consistent with the behavior of if. Example model that illustrates both behaviors below.

entity A:
    string name
    bool condition
end
implement A using conditional when self.condition
implement A using always

implementation conditional for A:
    std::print(f"implementation triggered for {self.name}!")
end
implementation always for A:
    if self.condition:
        std::print(f"if body triggered for {self.name}!")
    end
end


unknown = std::get_env("THIS_ENV_VAR_DOES_NOT_EXIST")

A(name="true", condition=true)
A(name="false", condition=false)
A(name="unknown", condition=unknown)

The output is

implementation triggered for true!
implementation triggered for unknown!
if body triggered for true!

[sanderr]

Confirmed for iso 7.0.0 (and master at the time of writing). Have not tried for any versions older than that.