In the Rust std, `set_var` and `remove_var` will correctly require using an `unsafe {}` block in the next edition (2024). The documentation does now mention the safety issue but obviously it was a mistake to make these functions safe originally (albeit a mistake even higher level languages have made).
There is a patch for glibc which makes `getenv` safe in more cases where the environment is modified but C still allows direct access to the environ so it can't be completely safe in the face of modification https://github.com/bminor/glibc/commit/7a61e7f557a97ab597d6f...
https://doc.rust-lang.org/stable/std/env/fn.set_var.html
There is a patch for glibc which makes `getenv` safe in more cases where the environment is modified but C still allows direct access to the environ so it can't be completely safe in the face of modification https://github.com/bminor/glibc/commit/7a61e7f557a97ab597d6f...