Command::env()/env_remove() freeze the parent's environment

[oconnor663]

An example:

use std::process::Command;
use std::env;

fn main() {
    // Create a command to echo $foo.
    let mut c = Command::new("bash");
    c.arg("-c").arg("echo $foo");

    // Set an unrelated variable. This caches the current environment.
    c.env("UNRELATED_VARIABLE", "junk");

    // Define $foo in the parent. This has no effect on the child,
    // because of the line above!
    env::set_var("foo", "FOO IS DEFINED!!!");

    c.spawn().unwrap();
}

This program will run echo $foo, which prints an empty line because $foo is not defined in the child. But if we delete the line that sets $UNRELATED_VARIABLE and run again, we see FOO IS DEFINED!!! in the child's output.

The problem is that (at least in the unix implementation) the init_env_map function caches the parent's environment the first time it's called. My preferred behavior would be that Command never caches anything from the parent, and instead reads the environment at the time the child is spawned. Does anyone know of code relying on the current behavior?

[alexcrichton]

cc #28975, a similar issue

[oconnor663]

Definitely a dupe. I'll close this one.