Problem

When a build.rs script emits cargo:rerun-if-env-changed, it is not re-run when the value of the specified variable is changed via the env configuration.

Steps

build.rs:

pub fn main() {
    println!("cargo:rerun-if-env-changed=FOO");
    if let Ok(foo) = std::env::var("FOO") {
        assert!(&foo != "bad");
    }
}

.cargo/config.toml:

[env]
FOO = "good"

1. Run cargo build, it succeeds.
2. Change .cargo/config.toml to this:

[env]
FOO = "bad"

3. Run cargo build again, and it uses the cached build and succeeds. It should run build.rs again, and it should fail.

Workaround

4. Run FOO=bar cargo build, ignore the result.
5. Run cargo build again, now it runs build.rs with FOO=bad from the config and fails as expected.

Possible Solution(s)

No response

Notes

No response

Version

cargo 1.58.0 (7f08ace4f 2021-11-24)
release: 1.58.0
commit-hash: 7f08ace4f1305de7f3b1b0e2f765911957226bd4
commit-date: 2021-11-24
host: x86_64-unknown-linux-gnu
libgit2: 1.3.0 (sys:0.13.23 vendored)
libcurl: 7.80.0-DEV (sys:0.4.51+curl-7.80.0 vendored ssl:OpenSSL/1.1.1l)
os: Debian 11 (bullseye) [64-bit]