Flag `env!` macro usage in build scripts

[d-e-s-o]

What it does

I am not sure if lints can or should make assumptions about the file they are defined in, but it would be good to flag usage of the env! (and option_env!) macro in build scripts. In all likelihood this is wrong. It certainly is wrong for CARGO_* variables [0].

Advantage

It is easy to miss this wrong usage, as it may not break immediately.

Drawbacks

None that I can think of.

Example

env!("CARGO_PKG_VERSION")

Could be written as:

std::env::var("CARGO_PKG_VERSION").expect("CARGO_PKG_VERSION variable not set")

Comparison with existing lints

Not aware of existing lints doing something similar.

Additional Context

No response