Testing macros for accidental leaks

[Soni]

Current test framework only tests success or panics. With macros, they aren’t always fully hygienic, so sometimes you wanna test your own hygiene.

Take for example eventbus. This shouldn’t compile:

#[macro_use]
extern crate eventbus;

use eventbus::{Event, EventBus};

struct MyEvent {
    i: i32
}

impl Event for MyEvent {
}

#[test]
fn test_hygiene() {
    let bus = [EventBus::new()];
    let mut event = MyEvent { i: 3 };
    post_event!(&bus[EVENT_ID.load(::std::sync::atomic::Ordering::Relaxed)], MyEvent, &mut event);
}

And (as of eventbus 0.4.0) it doesn’t, but there’s no way to automatically test it.

[Nemo157]

There’s two options I know of for testing whether something doesn’t compile:

1. compile_fail doc test
2. compiletest_rs

[Soni]

The former is uh, how would I even use that?

The latter doesn’t work on stable.

[Nemo157]

compiletest_rs does actually have a stable feature to run on stable, the PR is the only sort of documentation of it I can find: https://github.com/laumann/compiletest-rs/pull/107

[Soni]

It builds on stable, but I’d hardly say it works on stable.

[dtolnay]

I am very confused about that comment. For your use case it would work exactly the same on stable.

[Soni]

compiletest-rs’s compile-fail tests don’t work on stable. I tried it.

[dtolnay]

I can’t guess what you did wrong, but I can assure you that it does work on stable.

For example try running cargo +stable test against this directory of ref-cast, or cargo +stable test --features compiletest against this directory of indoc.

[Soni]

wait, those aren’t testing the parent crate directly…

they aren’t using src/lib.rs and tests/…

I guess that’s what I did wrong, yeah? (edit: nope, still doesn’t work)

anyway, would still be nicer if they were built-in.

[dtolnay]

I still can’t guess what you are doing, but that’s not it either. It works exactly the same if you move those tests directly into the main crate. You can see this PR passing in CI against stable, beta, and nightly: https://github.com/dtolnay/ref-cast/pull/6

I prefer to keep them separate only because it is not possible to have optional dev-dependencies at the moment (this is tracked in rust-lang/cargo#1596). If I need to run my crate’s tests against an older version of rustc than the one required by compiletest_rs, this way makes it easier.

[Soni]

maybe I’m accidentally using an older rustc? .-.

[Uther]

The perfect solution would be a #[should_not_compile] attribute with a optional rustc error code.

It would probably require cargo test to generate for each of these test a rs file with all the other tests removed (so the failing test can be identified) and try to compile them. It would probably slow down test a lot, even if code generation can be skipped.

[system]

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