User Story: Using literals in function call

[Emilgardis]

Lint explanation

In cross there is a function which when called with a literal is most often wrong.

Example code

pub fn bool_from_envvar(envvar: &str) -> bool {
    if let Ok(value) = bool::from_str(envvar) {
        value
    } else if let Ok(value) = i32::from_str(envvar) {
        value != 0
    } else {
        !envvar.is_empty()
    }
}

// correct
bool_from_envvar(std::env::var("FOO")?);

// incorrect
bool_from_envvar("FOO");

Notes

Being able to say "this parameter on this function should not be from a literal" would be helpful here.

[Alexhuszagh]

It might also be worth mentioning that for certain cases, only 0, 1, true, false are allowed, or another set of accepted values (we couldn't do that in our application due to backwards compatibility concerns).

[xFrednet]

Thank you for the user story. Testing for literals and allowing specific literals is definitely planned :)