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<main>
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<h1 id="rust-新版解读--172--feature启用提示"><a class="header" href="#rust-新版解读--172--feature启用提示">Rust 新版解读 | 1.72 | feature启用提示</a></h1>
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<blockquote>
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<p>Rust 1.72 官方 release doc: <a href="https://blog.rust-lang.org/2023/08/24/Rust-1.72.0.html">Announcing Rust 1.72.0 | 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 1.72 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="警告可能有用的-cfg-禁用项"><a class="header" href="#警告可能有用的-cfg-禁用项">警告可能有用的 <code>cfg</code> 禁用项</a></h2>
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<p>一直以来都支持的通过 <code>cfg</code> 条件编译部分代码，例如在开启特定 feature 时的函数，或者针对特定平台的逻辑。之前编译器会直接无视掉这些代码，现在会记录这些符号名称和对应的 <code>cfg</code> 条件，因此可以警告你正在调用一个特定 feature 下的函数，需要启用 feature：</p>
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<pre><code class="language-text"> Compiling my-project v0.1.0 (/tmp/my-project)
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error[E0432]: unresolved import `rustix::io_uring`
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--> src/main.rs:1:5
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1 | use rustix::io_uring;
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| ^^^^^^^^^^^^^^^^ no `io_uring` in the root
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note: found an item that was configured out
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--> /home/username/.cargo/registry/src/index.crates.io-6f17d22bba15001f/rustix-0.38.8/src/lib.rs:213:9
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213 | pub mod io_uring;
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| ^^^^^^^^
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= note: the item is gated behind the `io_uring` feature
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For more information about this error, try `rustc --explain E0432`.
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error: could not compile `my-project` (bin "my-project") due to previous error
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</code></pre>
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<h2 id="不受限制的常量计算时间"><a class="header" href="#不受限制的常量计算时间">不受限制的常量计算时间</a></h2>
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<p>之前为了避免用户自定义的常量在编译期间进行估算时，陷入死循环或占用无限制的时间，Rust 之前会限制用作常量计算的语句数目。然而一些特殊的有创造性的 Rust 代码还是会超过这个限制，进而产生编译错误；更糟糕的情况是，是否达到限制的是会随着用户调用库的不同而变化的。</p>
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<p>现在，可以在编译时执行无限制的常量计算。而为了避免长时间编译没有反馈，编译器会在编译时代码运行一段时间后发出一条消息，并在每次翻倍的一段时间后重复该消息。默认情况下，编译器还将在捕获无限循环的大量步骤后报错提示 <code>const_eval_long_run</code> ，但可以用 <code>allow(const_eval_long_run)</code> 允许特别长的常量计算。</p>
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<h2 id="clippy-lints-上升到-rustc"><a class="header" href="#clippy-lints-上升到-rustc">Clippy lints 上升到 rustc</a></h2>
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<p>几个原本由 Clippy 提供的 lints，提升到 rustc 里：</p>
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<ul>
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<li><a href="https://rust-lang.github.io/rust-clippy/rust-1.71.0/index.html#undropped_manually_drops"><code>clippy::undropped_manually_drops</code></a> => <a href="https://doc.rust-lang.org/1.72.0/rustc/lints/listing/deny-by-default.html#undropped-manually-drops"><code>undropped-manually-drops</code></a> (deny)
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<ul>
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<li>无作用的 <code>ManullyDrop</code></li>
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</ul>
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</li>
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<li><a href="https://rust-lang.github.io/rust-clippy/rust-1.71.0/index.html#invalid_utf8_in_unchecked"><code>clippy::invalid_utf8_in_unchecked</code></a> => <a href="https://doc.rust-lang.org/1.72.0/rustc/lints/listing/deny-by-default.html#invalid-from-utf8-unchecked"><code>invalid_from_utf8_unchecked</code></a> (deny) 或 <a href="https://doc.rust-lang.org/1.72.0/rustc/lints/listing/warn-by-default.html#invalid-from-utf8"><code>invalid_from_utf8</code></a> (warn)
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<ul>
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<li>检查调用 <code>std::str::from_utf8_unchecked</code> 和 <code>std::str::from_utf8_unchecked_mut</code> 转换不合法的 UTF-8 字面量，这会违反了 safety 前提，导致未定义行为</li>
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<li>检查 <code>std::str::from_utf8</code> 和 <code>std::str::from_utf8_mut</code> 转换不合法的 UTF-8 字面量，这会永远返回错误。</li>
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</ul>
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</li>
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<li><a href="https://rust-lang.github.io/rust-clippy/rust-1.71.0/index.html#cmp_nan"><code>clippy::cmp_nan</code></a> => <a href="https://doc.rust-lang.org/1.72.0/rustc/lints/listing/warn-by-default.html#invalid-nan-comparisons"><code>invalid_nan_comparisons</code></a> (warn)
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<ul>
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<li>检查使用 <code>f32::NAN</code> 或者 <code>f64::NAN</code> 参与比较，<code>NAN</code> 在比较时无任何意义，即使与自己比较也是无意义行为，建议使用 <code>is_nan()</code> 方法</li>
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</ul>
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</li>
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<li><a href="https://rust-lang.github.io/rust-clippy/rust-1.71.0/index.html#cast_ref_to_mut"><code>clippy::cast_ref_to_mut</code></a> => <a href="https://doc.rust-lang.org/1.72.0/rustc/lints/listing/allowed-by-default.html#invalid-reference-casting"><code>invalid_reference_casting</code></a> (allow)
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<ul>
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<li>检查不使用内部可变性的从 <code>&T</code> 到 <code>&mut T</code> 的转换，这会导致未定义行为。当前这个lint本身还有些问题，所以是 <code>allow</code> 级别，预计会在 1.73 版本修正后变为默认 <code>deny</code></li>
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</ul>
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</li>
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</ul>
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<h2 id="未来对-windows-的支持"><a class="header" href="#未来对-windows-的支持">未来对 Windows 的支持</a></h2>
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<p>未来的 release 版本里会放弃对 win10 以前的系统的官方支持，Rust 1.75 将成为最后一个支持 windows 7,8,8.1的版本，2024 年 2 月起的 rust 1.76 将仅支持 win10 及后续版本 （ target : tier-1 ）。详情见提案 <a href="https://github.com/rust-lang/compiler-team/issues/651">MCP 651</a></p>
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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/2023/08/24/Rust-1.72.0.html#stabilized-apis">原Blog</a></p>
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