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<main>
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<h1 id="rust-新版解读--184--const-能力拓展"><a class="header" href="#rust-新版解读--184--const-能力拓展">Rust 新版解读 | 1.84 | Const 能力拓展</a></h1>
|
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<blockquote>
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<p>Rust 1.84 官方 release doc: <a href="https://blog.rust-lang.org/2025/01/09/Rust-1.84.0.html">Announcing Rust 1.84.0 | 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 1.84 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="cargo-在依赖版本选择中考虑-rust-版本"><a class="header" href="#cargo-在依赖版本选择中考虑-rust-版本">Cargo 在依赖版本选择中考虑 Rust 版本</a></h2>
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|
|
<p>1.84.0 稳定了支持最低 Rust 版本（MSRV, minimum supported Rust version）的解析器，该解析器优先选择与项目声明的 MSRV （<code>Cargo.toml</code> 里的 <code>package.rust_version</code>） 兼容的依赖版本。通过支持 MSRV 的版本选择，维护者可以减少支持旧工具链的工作量，因为不再需要为每个依赖手动选择旧版本。</p>
|
|
|
<p>你可以通过 <code>.cargo/config.toml</code> 启用支持 MSRV 的解析器：</p>
|
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|
<pre><code class="language-toml">[resolver]
|
|
|
incompatible-rust-versions = "fallback"
|
|
|
</code></pre>
|
|
|
<p>然后在添加依赖时：</p>
|
|
|
<pre><code class="language-bash">$ cargo add clap
|
|
|
Updating crates.io index
|
|
|
warning: ignoring clap@4.5.23 (which requires rustc 1.74) to maintain demo's rust-version of 1.60
|
|
|
Adding clap v4.0.32 to dependencies
|
|
|
Updating crates.io index
|
|
|
Locking 33 packages to latest Rust 1.60 compatible versions
|
|
|
Adding clap v4.0.32 (available: v4.5.23, requires Rust 1.74)
|
|
|
</code></pre>
|
|
|
<p>在 CI 中<a href="https://doc.rust-lang.org/cargo/guide/continuous-integration.html#verifying-latest-dependencies">验证最新依赖</a>时，你可以覆盖此行为：</p>
|
|
|
<pre><code class="language-bash">$ CARGO_RESOLVER_INCOMPATIBLE_RUST_VERSIONS=allow cargo update
|
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Updating crates.io index
|
|
|
Locking 12 packages to latest compatible versions
|
|
|
Updating clap v4.0.32 -> v4.5.23
|
|
|
</code></pre>
|
|
|
<p>你也可以通过在 <code>Cargo.toml</code> 清单文件中设置 <a href="https://doc.rust-lang.org/cargo/reference/resolver.html#resolver-versions"><code>package.resolver = "3"</code></a> 来启用此功能，但这需要将 MSRV 提升到 1.84。对于使用 Rust 2024 的项目（将在 1.85 中稳定），新的解析器将默认启用。</p>
|
|
|
<p>这为库作者在决定采用新 Rust 工具链功能的策略时提供了更大的灵活性。以前，库采用新 Rust 工具链的功能会迫使使用旧 Rust 版本的下游用户要么升级工具链，要么手动选择与工具链兼容的旧版本库（并避免运行 <code>cargo update</code>）。现在，这些用户将能够自动使用与其旧工具链兼容的旧库版本。</p>
|
|
|
<p>有关决定 MSRV 策略时的更多注意事项，请参阅<a href="https://doc.rust-lang.org/cargo/reference/rust-version.html#setting-and-updating-rust-version">文档</a>。</p>
|
|
|
<h2 id="新-trait-求解器的迁移开始"><a class="header" href="#新-trait-求解器的迁移开始">新 trait 求解器的迁移开始</a></h2>
|
|
|
<p>Rust 编译器正在迁移到新的 trait 求解器实现。下一代 trait 求解器是 Rust 类型系统核心组件的重新实现。它不仅负责检查 trait 边界（例如 <code>Vec<T>: Clone</code>）是否成立，还被类型系统的许多其他部分使用，例如规范化（确定 <code><Vec<T> as IntoIterator>::Item</code> 的基础类型）和类型等价（检查 <code>T</code> 和 <code>U</code> 是否相同）。</p>
|
|
|
<p>在 1.84 中，新求解器用于检查 trait 实现的一致性。从高层次来看，一致性负责确保在考虑其他 crate 中尚未编写或不可见的代码时，给定类型的 trait 实现最多只有一个。</p>
|
|
|
<p>此稳定化修复了旧实现中的一些主要理论上的正确性问题，导致可能会报告以前未报告的“trait 冲突实现”错误。根据 <a href="https://github.com/rust-lang/crater/">Crater</a> 对可用代码的评估，我们预计受影响的模式非常罕见。此次稳定版本还提高了我们证明实现不重叠的能力，在某些情况下允许编写更多代码。</p>
|
|
|
<p>有关更多详细信息，请参阅之前的<a href="https://blog.rust-lang.org/inside-rust/2024/12/04/trait-system-refactor-initiative.html">博客文章</a>和<a href="https://github.com/rust-lang/rust/pull/130654">稳定报告</a>。</p>
|
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<h2 id="严格来源-api"><a class="header" href="#严格来源-api">严格来源 API</a></h2>
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|
<p>在 Rust 中，<a href="https://rust-lang.github.io/rfcs/3559-rust-has-provenance.html">指针不仅仅是“整数”或“地址”</a>。例如，“释放后使用”是未定义行为，即使你“幸运”并且在读取/写入之前重新分配了释放的内存。另一个例子是，通过从 <code>&i32</code> 引用派生的指针写入是未定义行为，即使通过不同指针写入同一地址是合法的。这里的底层模式是，指针的计算方式很重要，而不仅仅是计算结果的地址。因此，我们说指针具有<strong>来源</strong>：要完全描述 Rust 中与指针相关的未定义行为，我们不仅需要知道指针指向的地址，还需要跟踪它是从哪些其他指针“派生”的。</p>
|
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<p>大多数情况下，程序员不需要过多担心来源，指针的派生方式非常清晰。然而，当将指针转换为整数并返回时，结果指针的来源是不明确的。在此版本中，Rust 添加了一组 API，可以在许多情况下替代整数指针转换的使用，从而避免此类转换固有的歧义。特别是，现在可以在不将指针转换为整数(或反方向将整数转换成指针)的情况下实现使用对齐指针的最低有效位存储额外信息的模式。这使得代码更易于推理，更易于编译器分析，并且还有益于像 <a href="https://github.com/rust-lang/miri">Miri</a> 这样的工具和像 <a href="https://www.cl.cam.ac.uk/research/security/ctsrd/cheri/">CHERI</a> 这样的架构，旨在检测和诊断指针滥用。</p>
|
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|
<p>有关更多详细信息，请参阅标准库中关于<a href="https://doc.rust-lang.org/std/ptr/index.html#provenance">来源</a>的文档。</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，包括上述 <code>provenance</code> 相关 API，参考<a href="https://blog.rust-lang.org/2025/01/09/Rust-1.84.0.html#stabilized-apis">原Blog</a></p>
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