9896beb5b5
I attempted to implement the lint in two steps. My first attempt was a default-warn lint about *all* unused results. While this attempt did indeed find many possible bugs, I felt that the false-positive rate was too high to be turned on by default for all of Rust. My second attempt was to make unused-result a default-allow lint, but allow certain types to opt-in to the notion of "you must use this". For example, the Result type is now flagged with #[must_use]. This lint about "must use" types is warn by default (it's different from unused-result). The unused_must_use lint had a 100% hit rate in the compiler, but there's not that many places that return Result right now. I believe that this lint is a crucial step towards moving away from conditions for I/O (because all I/O will return Result by default). I'm worried that this lint is a little too specific to Result itself, but I believe that the false positive rate for the unused_result lint is too high to make it useful when turned on by default.
41 lines
1.1 KiB
Rust
41 lines
1.1 KiB
Rust
// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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#[deny(unused_result, unused_must_use)];
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#[allow(dead_code)];
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#[must_use]
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enum MustUse { Test }
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fn foo<T>() -> T { fail!() }
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fn bar() -> int { return foo::<int>(); }
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fn baz() -> MustUse { return foo::<MustUse>(); }
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#[allow(unused_result)]
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fn test() {
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foo::<int>();
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foo::<MustUse>(); //~ ERROR: unused result which must be used
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}
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#[allow(unused_result, unused_must_use)]
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fn test2() {
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foo::<int>();
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foo::<MustUse>();
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}
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fn main() {
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foo::<int>(); //~ ERROR: unused result
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foo::<MustUse>(); //~ ERROR: unused result which must be used
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let _ = foo::<int>();
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let _ = foo::<MustUse>();
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}
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