821d50aa0c
Warn about unused expressions with closure or generator type. This follows
existing precedence of must use annotations present on `FnOnce`, `FnMut`, `Fn`
traits, which already indirectly apply to closures in some cases, e.g.,:
```rust
fn f() -> impl FnOnce() {
|| {}
}
fn main() {
// an existing warning: unused implementer of `std::ops::FnOnce` that must be used:
f();
// a new warning: unused closure that must be used:
|| {};
}
```
41 lines
1002 B
Rust
41 lines
1002 B
Rust
// Test that closures and generators are "must use" types.
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// edition:2018
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#![feature(async_closure)]
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#![feature(const_in_array_repeat_expressions)]
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#![feature(generators)]
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#![deny(unused_must_use)]
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fn unused() {
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|| { //~ ERROR unused closure that must be used
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println!("Hello!");
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};
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async {}; //~ ERROR unused implementer of `std::future::Future` that must be used
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|| async {}; //~ ERROR unused closure that must be used
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async || {}; //~ ERROR unused closure that must be used
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[Box::new([|| {}; 10]); 1]; //~ ERROR unused array of boxed arrays of closures that must be used
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[|| { //~ ERROR unused array of generators that must be used
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yield 42u32;
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}; 42];
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vec![|| "a"].pop().unwrap(); //~ ERROR unused closure that must be used
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let b = false;
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|| true; //~ ERROR unused closure that must be used
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println!("{}", b);
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}
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fn ignored() {
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let _ = || {};
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let _ = || yield 42;
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}
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fn main() {
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unused();
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ignored();
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}
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