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<main>
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<h1 id="rust-新版解读--181--expect-lint"><a class="header" href="#rust-新版解读--181--expect-lint">Rust 新版解读 | 1.81 | <code>expect</code> lint</a></h1>
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<blockquote>
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<p>Rust 1.81 官方 release doc: <a href="https://blog.rust-lang.org/2024/09/05/Rust-1.81.0.html">Announcing Rust 1.81.0 | Rust Blog</a></p>
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</blockquote>
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<p>通过 <a href="https://www.rust-lang.org/tools/install">rustup</a> 安装的同学可以使用以下命令升级到 1.81 版本:</p>
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<pre><code class="language-shell">$ rustup update stable
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</code></pre>
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<h2 id="coreerrorerror"><a class="header" href="#coreerrorerror"><code>core::error::Error</code></a></h2>
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<p>1.81 版本稳定了 <code>core::error::Error</code> trait，允许在 core 中使用 Error trait，使得库可以在 #![no_std] 环境中使用。这主要是为了让 Rust 生态系统能够在不同的环境中标准化相同的 Error trait，无论库的目标环境是什么。</p>
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<h2 id="新的排序实现"><a class="header" href="#新的排序实现">新的排序实现</a></h2>
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<p>标准库中的稳定和不稳定排序实现都已更新为新算法，提高了运行时性能和编译时间。</p>
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<p>此外，新的排序算法都会尝试检测 <code>Ord</code> 的不正确实现，这些实现会阻止它们能够产生有意义的排序结果，并且现在会在这些情况下 panic，而不是返回实际上是随机排列的数据。遇到这些 panic 的用户应该审查他们的排序实现，以确保它们满足 <a href="https://doc.rust-lang.org/nightly/std/cmp/trait.PartialOrd.html"><code>PartialOrd</code></a> 和 <a href="https://doc.rust-lang.org/nightly/std/cmp/trait.Ord.html"><code>Ord</code></a> 的要求。</p>
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<h2 id="expectlint"><a class="header" href="#expectlint"><code>#[expect(lint)]</code></a></h2>
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<p>1.81 版本引入了一个新的 lint 级别 <code>expect</code>，允许显式地指定一个特定的 lint <strong>应该发生</strong>，并在没有发生时发出警告。这个功能的预期用例是暂时消除一个 lint，无论是由于 lint 实现错误还是正在进行的重构，同时希望在不再需要 lint 时得到通知。</p>
|
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<p>例如，如果您正在移动代码库以符合通过 Clippy lint 强制执行的新限制，比如 <a href="https://rust-lang.github.io/rust-clippy/stable/index.html#/undocumented_unsafe_blocks"><code>undocumented_unsafe_blocks</code></a>，您可以在过渡期间使用 <code>#[expect(clippy::undocumented_unsafe_blocks)]</code>，确保一旦所有的 unsafe 块都被文档化，您可以选择拒绝 lint 以强制执行它。</p>
|
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<p>Clippy 还有两个 lint 来强制使用这个特性，并帮助迁移现有的属性：</p>
|
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<p><a href="https://rust-lang.github.io/rust-clippy/master/index.html#/allow_attributes"><code>clippy::allow_attributes</code></a> 限制 <code>#[allow]</code> 属性，鼓励使用 <code>#[expect]</code> 或将 <code>#[allow]</code> 属性迁移到 <code>#[expect]</code>
|
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|
<a href="https://rust-lang.github.io/rust-clippy/master/index.html#/allow_attributes_without_reason"><code>clippy::allow_attributes_without_reason</code></a> 要求为 <code>#[allow]</code> 属性提供原因</p>
|
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<h2 id="lint-reasons"><a class="header" href="#lint-reasons"><code>Lint reasons</code></a></h2>
|
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<p>更改 lint 级别通常是出于某种特定原因。例如，如果代码在没有浮点支持的环境中运行，您可以使用 Clippy 如 <code>#![deny(clippy::float_arithmetic)]</code> 来阻止此类使用。然而，如果项目中的新开发人员看到这个 lint，他们可能需要在 deny 的注释里（如果有的话）寻找原因。从 Rust 1.81 开始，他们可以直接在编译器消息中得到通知：</p>
|
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<pre><code class="language-bash">error: floating-point arithmetic detected
|
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--> src/lib.rs:4:5
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4 | a + b
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| ^^^^^
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= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#float_arithmetic
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= note: no hardware float support
|
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note: the lint level is defined here
|
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--> src/lib.rs:1:9
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1 | #![deny(clippy::float_arithmetic, reason = "no hardware float support")]
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| ^^^^^^^^^^^^^^^^^^^^^^^^
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</code></pre>
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<h2 id="others"><a class="header" href="#others">Others</a></h2>
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<p>其它更新细节，和稳定的 API 列表，参考<a href="https://blog.rust-lang.org/2024/09/05/Rust-1.81.0.html#stabilized-apis">原Blog</a></p>
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