programmingrust / antisamples

Test programs that should not compile.

Programming Rust Antisamples

This repository contains some tests for the code in our book, Programming Rust.

These tests are a little unusual: none of them compile. In fact, if any do compile and run, it's a bug! These are the tests for code samples in our book that are there to illustrate errors. The tests check that rustc agrees they are erroneous. They also help us notice when a new rustc version has different error messages, so we can update the book.

We're publishing these so that you can copy and paste our anti-examples into play.rust-lang.org and tinker with them. (You could also copy them out of the book, but often what's in the book is just a fragment, not a complete program.)

Whenever you see a compiler error message in the book:

use std::thread;

fn start_sorting_thread(mut cities: Vec<City>, stat: Statistic)
    -> thread::JoinHandle<Vec<City>>
{
    let key_fn = |city: &City| -> i64 { -city.get_statistic(stat) };

    thread::spawn(|| {
        cities.sort_by_key(key_fn);
        cities
    })
}

Again, the closure key_fn contains a reference to stat. But this time, Rust can't guarantee that the reference is used safely. Rust therefore rejects this program:

error[E0373]: closure may outlive the current function, but it borrows `stat`,
              which is owned by the current function
  --> closures_sort_thread.rs:33:18
   |
33 | let key_fn = |city: &City| -> i64 { -city.get_statistic(stat) };
   |              ^^^^^^^^^^^^^^^^^^^^                       ^^^^
   |              |                                      `stat` is borrowed here
   |              may outlive borrowed value `stat`

you'll find the filename in the error message (rustc prints it right after an arrow, -->):

  --> closures_sort_thread.rs:33:18

The source file will be under either tests/compile-fail or (rarely) tests/parse-fail.

In this case, it's tests/compile-fail/closures_sort_thread.rs.

Happy hacking!

—@jimblandy & @jorendorff

How to run^* these tests

^*(of course they do not actually "run", as such)

You probably don't care about this unless you're working on the book. These tests use the compiletest_rs crate, which requires Nightly Rust. To set up Nightly Rust:

$ rustup install nightly

To run the tests:

$ cargo test

License

The example code in this directory and its subdirectories is licensed under the terms of the MIT license. See LICENSE-MIT for details.