Don't panic on std::env::vars() when env is null.

[BurntPizza]

Fixes#53200.

Reviewer(s):

• Do I need to do any #[cfg()] here?
• Is this use of libc ok for a dev-dependency?

[rust-highfive]

r? @joshtriplett

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[joshtriplett]

The change itself seems completely reasonable to me; good catch.

I don't know whether you can use libc here. And even if you can, does the test get isolated such that the use of clearenv doesn't affect other tests?

[BurntPizza]

It seems to, it runs first anyway, and they all pass. That was a concern for me as well.

[BurntPizza]

The only other thing is trusting environ() to return a non-null. I haven't looked at docs for stuff like _NSGetEnviron, and it hasn't been an issue but it still gives me some heeby-jeebies.

[joshtriplett]

Wouldn't other tests (not just the environment tests) get compiled into the same binary? I'm concerned about the tests being fragile.

[BurntPizza]

The binary that runs is build/x86_64-unknown-linux-gnu/stage1-std/x86_64-unknown-linux-gnu/release/deps/env-a962c0d6d7770051 (when doing ./x.py test --stage 1 src/libstd) so I don't think so.
Should I save-and-restore the env?

[joshtriplett]

@BurntPizza Ah, OK. No objection in that case, but I don't know if you can use libc here.

[BurntPizza]

The main Cargo.toml for libstd uses the same libc_shim import as a regular dependency, so I think it's ok.
cc @alexcrichton Could you or someone who would know weigh in on this?

[alexcrichton]

Thanks for the PR! The dev-dependency here should work out fine but @joshtriplett is right in that this shouldn't be executing in the main body of tests. Rather can a new entirely standalone program be added to src/test/run-pass to execute this test? That also avoids the need to have a libc dev-dep.

Finally I do think that this'll need a #[cfg(target_os = "linux")] marker probably, it likely won't pass on Windows and some other obscure platforms here and there.

[BurntPizza]

Rebased with changes.

[alexcrichton]

@bors: r+

Thanks!

[bors]

📌 Commit c9aca02 has been approved by alexcrichton