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< h1 id = "依赖覆盖" > < a class = "header" href = "#依赖覆盖" > 依赖覆盖< / a > < / h1 >
< p > 依赖覆盖对于本地开发来说，是很常见的，大部分原因都是我们希望在某个包发布到 < code > crates.io< / code > 之前使用它，例如：< / p >
< ul >
< li > 你正在同时开发一个包和一个项目，而后者依赖于前者，你希望能在该项目中对正在开发的包进行测试< / li >
< li > 你引入的一个依赖包在 < code > master< / code > 分支发布了新的代码，恰好修复了某个 bug， < / li >
< li > 你即将发布一个包的新版本，为了确保新版本正常工作，你需要对其进行集成测试< / li >
< li > 你为项目的某个依赖包提了一个 PR 并解决了一个重要 bug， < code > master< / code > 分支，但是时间不等人，因此你决定先使用自己修改的版本，等未来合并后，再继续使用官方版本< / li >
< / ul >
< p > 下面我们来具体看看类似的问题该如何解决。< / p >
< blockquote >
< p > 上一章节中我们讲了如果通过< a href = "https://course.rs/cargo/reference/specify-deps/intro.html#多引用方式混合" > 多种引用方式< / a > 来引入一个包，其实这也是一种依赖覆盖。< / p >
< / blockquote >
< h2 id = "测试-bugfix-版本" > < a class = "header" href = "#测试-bugfix-版本" > 测试 bugfix 版本< / a > < / h2 >
< p > 假设我们有一个项目正在使用 < a href = "https://crates.io/crates/uuid" > < code > uuid< / code > < / a > 依赖包，但是却不幸地发现了一个 bug， < / p >
< p > 我们项目的 < code > Cargo.toml< / code > 内容如下：< / p >
< pre > < code class = "language-toml" > [package]
name = "my-library"
version = "0.1.0"
[dependencies]
uuid = "0.8.2"
< / code > < / pre >
< p > 为了修复 < code > bug< / code > ，首先需要将 < code > uuid< / code > 的源码克隆到本地，笔者是克隆到和项目同级的目录下:< / p >
< pre > < code class = "language-shell" > git clone https://github.com/uuid-rs/uuid
< / code > < / pre >
< p > 下面，修改项目的 < code > Cargo.toml< / code > 添加以下内容以引入本地克隆的版本:< / p >
< pre > < code class = "language-toml" > [patch.crates-io]
uuid = { path = "../uuid" }
< / code > < / pre >
< p > 这里我们使用自己修改过的 < code > patch< / code > 来覆盖来自 < code > crates.io< / code > 的版本，由于克隆下来的 < code > uuid< / code > 目录和我们的项目同级，因此通过相对路径 “../uuid” 即可定位到。< / p >
< p > 在成功为 < code > uuid< / code > 打了本地补丁后，现在尝试在项目下运行 < code > cargo build< / code > ，但是却报错了，而且报错内容有一些看不太懂：< / p >
< pre > < code class = "language-shell" > $ cargo build
Updating crates.io index
warning: Patch `uuid v1.0.0-alpha.1 (/Users/sunfei/development/rust/demos/uuid)` was not used in the crate graph.
Check that the patched package version and available features are compatible
with the dependency requirements. If the patch has a different version from
what is locked in the Cargo.lock file, run `cargo update` to use the new
version. This may also occur with an optional dependency that is not enabled.
< / code > < / pre >
< p > 具体原因比较复杂，但是仔细观察，会发现克隆下来的 < code > uuid< / code > 的版本是 < code > v1.0.0-alpha.1< / code > (在 < code > "../uuid/Cargo.toml"< / code > 中可以查看)，然后我们本地引入的 < code > uuid< / code > 版本是 < code > 0.8.2< / code > ，根据之前讲过的 < code > crates.io< / code > 的< a href = "https://course.rs/cargo/reference/specify-deps/intro.html#从-cratesio-引入依赖包" > 版本规则< / a > ，这两者是不兼容的，< code > 0.8.2< / code > 只能升级到 < code > 0.8.z< / code > ，例如 < code > 0.8.3< / code > 。< / p >
< p > 既然如此，我们先将 “../uuid/Cargo.toml” 中的 < code > version = "1.0.0-alpha.1"< / code > 修改为 < code > version = "0.8.3"< / code > ，然后看看结果先:< / p >
< pre > < code class = "language-shell" > $ cargo build
Updating crates.io index
Compiling uuid v0.8.3 (/Users/sunfei/development/rust/demos/uuid)
< / code > < / pre >
< p > 大家注意到最后一行了吗？我们成功使用本地的 < code > 0.8.3< / code > 版本的 < code > uuid< / code > 作为最新的依赖，因此也侧面证明了，补丁 < code > patch< / code > 的版本也必须遵循相应的版本兼容规则！< / p >
< p > 如果修改后还是有问题，大家可以试试以下命令，指定版本进行更新:< / p >
< pre > < code class = "language-shell" > % cargo update -p uuid --precise 0.8.3
Updating crates.io index
Updating uuid v0.8.3 (/Users/sunfei/development/rust/demos/uuid) -> v0.8.3
< / code > < / pre >
< p > 修复 bug 后，我们可以提交 pr 给 < code > uuid< / code > ，一旦 pr 被合并到了 < code > master< / code > 分支，你可以直接通过以下方式来使用补丁:< / p >
< pre > < code class = "language-toml" > [patch.crates-io]
uuid = { git = 'https://github.com/uuid-rs/uuid' }
< / code > < / pre >
< p > 等未来新的内容更新到 < code > crates.io< / code > 后，大家就可以移除这个补丁，直接更新 < code > [dependencies]< / code > 中的 < code > uuid< / code > 版本即可！< / p >
< h2 id = "使用未发布的小版本" > < a class = "header" href = "#使用未发布的小版本" > 使用未发布的小版本< / a > < / h2 >
< p > 还是 < code > uuid< / code > 包，这次假设我们要为它新增一个特性，同时我们已经修改完毕，在本地测试过，并提交了相应的 pr， < code > crates.io< / code > 之前继续使用。< / p >
< p > 再做一个假设，对于 < code > uuid< / code > 来说，目前 < code > crates.io< / code > 上的版本是 < code > 1.0.0< / code > ，在我们提交了 pr 并合并到 < code > master< / code > 分支后，< code > master< / code > 上的版本变成了 < code > 1.0.1< / code > ，这意味着未来 < code > crates.io< / code > 上的版本也将变成 < code > 1.0.1< / code > 。< / p >
< p > 为了使用新加的特性，同时当该包在未来发布到 < code > crates.io< / code > 后，我们可以自动使用 < code > crates.io< / code > 上的新版本，而无需再使用 < code > patch< / code > 补丁，可以这样修改 < code > Cargo.toml< / code > ： < / p >
< pre > < code class = "language-toml" > [package]
name = "my-library"
version = "0.1.0"
[dependencies]
uuid = "1.0.1"
[patch.crates-io]
uuid = { git = 'https://github.com/uuid-rs/uuid' }
< / code > < / pre >
< p > 注意，我们将 < code > [dependencies]< / code > 中的 < code > uuid< / code > 版本提前修改为 < code > 1.0.1< / code > ，由于该版本在 < code > crates.io< / code > 尚未发布，因此 < code > patch< / code > 版本会被使用。< / p >
< p > 现在，我们的项目是基于 < code > patch< / code > 版本的 < code > uuid< / code > 来构建，也就是从 < code > gihtub< / code > 的 < code > master< / code > 分支中拉取最新的 < code > commit< / code > 来构建。一旦未来 < code > crates.io< / code > 上有了 < code > 1.0.1< / code > 版本，那项目就会继续基于 < code > crates.io< / code > 来构建，此时，< code > patch< / code > 就可以删除了。< / p >
< h4 id = "间接使用-patch" > < a class = "header" href = "#间接使用-patch" > 间接使用 < code > patch< / code > < / a > < / h4 >
< p > 现在假设项目 < code > A< / code > 的依赖是 < code > B< / code > 和 < code > uuid< / code > ，而 < code > B< / code > 的依赖也是 < code > uuid< / code > ，此时我们可以让 < code > A< / code > 和 < code > B< / code > 都使用来自 < code > GitHub< / code > 的 < code > patch< / code > 版本，配置如下:< / p >
< pre > < code class = "language-toml" > [package]
name = "my-binary"
version = "0.1.0"
[dependencies]
my-library = { git = 'https://example.com/git/my-library' }
uuid = "1.0.1"
[patch.crates-io]
uuid = { git = 'https://github.com/uuid-rs/uuid' }
< / code > < / pre >
< p > 如上所示，< code > patch< / code > 不仅仅对于 < code > my-binary< / code > 项目有用，对于 < code > my-binary< / code > 的依赖 < code > my-library< / code > 来说，一样可以间接生效。< / p >
< h4 id = "非-cratesio-的-patch" > < a class = "header" href = "#非-cratesio-的-patch" > 非 crates.io 的 patch< / a > < / h4 >
< p > 若我们想要覆盖的依赖并不是来自 < code > crates.io< / code > ，就需要对 < code > [patch]< / code > 做一些修改。例如依赖是 < code > git< / code > 仓库，然后使用本地路径来覆盖它:< / p >
< pre > < code class = "language-toml" > [patch."https://github.com/your/repository"]
my-library = { path = "../my-library/path" }
< / code > < / pre >
< p > easy， < / p >
< h2 id = "使用未发布的大版本" > < a class = "header" href = "#使用未发布的大版本" > 使用未发布的大版本< / a > < / h2 >
< p > 现在假设我们要发布一个大版本 < code > 2.0.0< / code > ，与之前类似，可以将 < code > Cargo.toml< / code > 修改如下:< / p >
< pre > < code class = "language-toml" > [dependencies]
uuid = "2.0"
[patch.crates-io]
uuid = { git = "https://github.com/uuid-rs/uuid", branch = "2.0.0" }
< / code > < / pre >
< p > 此时 < code > 2.0< / code > 版本在 < code > crates.io< / code > 上还不存在，因此我们使用了 < code > patch< / code > 版本且指定了 < code > branch = "2.0.0"< / code > 。< / p >
< h4 id = "间接使用-patch-1" > < a class = "header" href = "#间接使用-patch-1" > 间接使用 < code > patch< / code > < / a > < / h4 >
< p > 这里需要注意，< strong > 与之前的小版本不同，大版本的 < code > patch< / code > 不会发生间接的传递！< / strong > ，例如：< / p >
< pre > < code class = "language-toml" > [package]
name = "my-binary"
version = "0.1.0"
[dependencies]
my-library = { git = 'https://example.com/git/my-library' }
uuid = "1.0"
[patch.crates-io]
uuid = { git = 'https://github.com/uuid-rs/uuid', branch = '2.0.0' }
< / code > < / pre >
< p > 以上配置中, < code > my-binary< / code > 将继续使用 < code > 1.x.y< / code > 系列的版本，而 < code > my-library< / code > 将使用最新的 < code > 2.0.0< / code > patch。< / p >
< p > 原因是， ， < / p >
< h2 id = "多版本patch" > < a class = "header" href = "#多版本patch" > 多版本[patch]< / a > < / h2 >
< p > 在之前章节，我们介绍过如何使用 < code > package key< / code > 来< a href = "https://course.rs/cargo/reference/specify-deps/intro.html#在-cargotoml-中重命名依赖" > 重命名依赖包< / a > ，现在来看看如何使用它同时引入多个 < code > patch< / code > 。< / p >
< p > 假设，我们对 < code > serde< / code > 有两个新的 < code > patch< / code > 需求:< / p >
< ul >
< li > < code > serde< / code > 官方解决了一个 < code > bug< / code > 但是还没发布到 < code > crates.io< / code > ，我们想直接从 < code > git< / code > 仓库的最新 < code > commit< / code > 拉取版本 < code > 1.*< / code > < / li >
< li > 我们自己为 < code > serde< / code > 添加了新的功能，命名为 < code > 2.0.0< / code > 版本，并将该版本上传到自己的 < code > git< / code > 仓库中< / li >
< / ul >
< p > 为了满足这两个 < code > patch< / code > ，可以使用如下内容的 < code > Cargo.toml< / code > ： < / p >
< pre > < code class = "language-toml" > [patch.crates-io]
serde = { git = 'https://github.com/serde-rs/serde' }
serde2 = { git = 'https://github.com/example/serde', package = 'serde', branch = 'v2' }
< / code > < / pre >
< p > 第一行说明，第一个 < code > patch< / code > 从官方仓库 < code > main< / code > 分支的最新 < code > commit< / code > 拉取，而第二个则从我们自己的仓库拉取 < code > v2< / code > 分支，同时将其重命名为 < code > serde2< / code > 。< / p >
< p > 这样，在代码中就可以分别通过 < code > serde< / code > 和 < code > serde2< / code > 引用不同版本的依赖库了。< / p >
< h2 id = "通过path来覆盖依赖" > < a class = "header" href = "#通过path来覆盖依赖" > 通过[path]来覆盖依赖< / a > < / h2 >
< p > 有时我们只是临时性地对一个项目进行处理，因此并不想去修改它的 < code > Cargo.toml< / code > 。此时可以使用 < code > Cargo< / code > 提供的路径覆盖方法: < strong > 注意，这个方法限制较多，如果可以，还是要使用 [patch]< / strong > 。< / p >
< p > 与 < code > [patch]< / code > 修改 < code > Cargo.toml< / code > 不同，路径覆盖修改的是 < code > Cargo< / code > 自身的< a href = "https://course.rs/cargo/guide/cargo-cache.html#cargo-home" > 配置文件< / a > < code > $Home/.cargo/config.toml< / code > :< / p >
< pre > < code class = "language-toml" > paths = ["/path/to/uuid"]
< / code > < / pre >
< p > < code > paths< / code > 数组中的元素是一个包含 < code > Cargo.toml< / code > 的目录(依赖包)，在当前例子中，由于我们只有一个 < code > uuid< / code > ，因此只需要覆盖它即可。目标路径可以是相对的，也是绝对的，需要注意，如果是相对路径，那是相对包含 < code > .cargo< / code > 的 < code > $Home< / code > 来说的。< / p >
< h2 id = "不推荐的replace" > < a class = "header" href = "#不推荐的replace" > 不推荐的[replace]< / a > < / h2 >
< blockquote >
< p > < code > [replace]< / code > 已经被标记为 < code > deprecated< / code > ，并将在未来被移除，请使用 < code > [patch]< / code > 替代< / p >
< / blockquote >
< p > 虽然不建议使用，但是如果大家阅读其它项目时依然可能会碰到这种用法:< / p >
< pre > < code class = "language-toml" > [replace]
"foo:0.1.0" = { git = 'https://github.com/example/foo' }
"bar:1.0.2" = { path = 'my/local/bar' }
< / code > < / pre >
< p > 语法看上去还是很清晰的，< code > [replace]< / code > 中的每一个 < code > key< / code > 都是 < code > Package ID< / code > 格式，通过这种写法可以在依赖图中任意挑选一个节点进行覆盖。< / p >
< / main >
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