mirror of https://github.com/rust-lang/book
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36 KiB
Markdown
1000 lines
36 KiB
Markdown
<!-- DO NOT EDIT THIS FILE.
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This file is periodically generated from the content in the `/src/`
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directory, so all fixes need to be made in `/src/`.
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-->
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[TOC]
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# More About Cargo and Crates.io
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So far, we’ve used only the most basic features of Cargo to build, run, and
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test our code, but it can do a lot more. In this chapter, we’ll discuss some of
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its other, more advanced features to show you how to do the following:
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* Customize your build through release profiles.
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* Publish libraries on *https://crates.i**o*.
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* Organize large projects with workspaces.
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* Install binaries from *https://crates.io*.
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* Extend Cargo using custom commands.
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Cargo can do even more than the functionality we cover in this chapter, so for
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a full explanation of all its features, see its documentation at
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*https://doc.rust-lang.org/cargo*.
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## Customizing Builds with Release Profiles
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In Rust, *release profiles* are predefined and customizable profiles with
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different configurations that allow a programmer to have more control over
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various options for compiling code. Each profile is configured independently of
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the others.
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Cargo has two main profiles: the `dev` profile Cargo uses when you run `cargo
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build`, and the `release` profile Cargo uses when you run `cargo build
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--release`. The `dev` profile is defined with good defaults for development,
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and the `release` profile has good defaults for release builds.
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These profile names might be familiar from the output of your builds:
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```
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$ cargo build
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Finished dev [unoptimized + debuginfo] target(s) in 0.0s
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$ cargo build --release
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Finished release [optimized] target(s) in 0.0s
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```
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The `dev` and `release` are these different profiles used by the compiler.
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Cargo has default settings for each of the profiles that apply when you haven’t
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explicitly added any `[profile.*]` sections in the project’s *Cargo.toml* file.
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By adding `[profile.*]` sections for any profile you want to customize, you
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override any subset of the default settings. For example, here are the default
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values for the `opt-level` setting for the `dev` and `release` profiles:
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Filename: Cargo.toml
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```
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[profile.dev]
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opt-level = 0
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[profile.release]
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opt-level = 3
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```
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The `opt-level` setting controls the number of optimizations Rust will apply to
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your code, with a range of 0 to 3. Applying more optimizations extends
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compiling time, so if you’re in development and compiling your code often,
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you’ll want fewer optimizations to compile faster even if the resultant code
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runs slower. The default `opt-level` for `dev` is therefore `0`. When you’re
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ready to release your code, it’s best to spend more time compiling. You’ll only
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compile in release mode once, but you’ll run the compiled program many times,
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so release mode trades longer compile time for code that runs faster. That is
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why the default `opt-level` for the `release` profile is `3`.
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You can override a default setting by adding a different value for it in
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*Cargo.toml*. For example, if we want to use optimization level 1 in the
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development profile, we can add these two lines to our project’s *Cargo.toml*
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file:
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Filename: Cargo.toml
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```
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[profile.dev]
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opt-level = 1
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```
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This code overrides the default setting of `0`. Now when we run `cargo build`,
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Cargo will use the defaults for the `dev` profile plus our customization to
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`opt-level`. Because we set `opt-level` to `1`, Cargo will apply more
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optimizations than the default, but not as many as in a release build.
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For the full list of configuration options and defaults for each profile, see
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Cargo’s documentation at
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*https://doc.rust-lang.org/cargo/reference/profiles.html*.
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## Publishing a Crate to Crates.io
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We’ve used packages from *https://crates.io* as dependencies of our project,
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but you can also share your code with other people by publishing your own
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packages. The crate registry at *https://crates.io* distributes the source code
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of your packages, so it primarily hosts code that is open source.
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Rust and Cargo have features that make your published package easier for people
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to find and use. We’ll talk about some of these features next and then explain
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how to publish a package.
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### Making Useful Documentation Comments
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Accurately documenting your packages will help other users know how and when to
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use them, so it’s worth investing the time to write documentation. In Chapter
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3, we discussed how to comment Rust code using two slashes, `//`. Rust also has
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a particular kind of comment for documentation, known conveniently as a
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*documentation comment*, that will generate HTML documentation. The HTML
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displays the contents of documentation comments for public API items intended
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for programmers interested in knowing how to *use* your crate as opposed to how
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your crate is *implemented*.
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Documentation comments use three slashes, `///`, instead of two and support
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Markdown notation for formatting the text. Place documentation comments just
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before the item they’re documenting. Listing 14-1 shows documentation comments
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for an `add_one` function in a crate named `my_crate`.
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Filename: src/lib.rs
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```
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/// Adds one to the number given.
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///
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/// # Examples
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///
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/// ```
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/// let arg = 5;
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/// let answer = my_crate::add_one(arg);
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///
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/// assert_eq!(6, answer);
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/// ```
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pub fn add_one(x: i32) -> i32 {
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x + 1
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}
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```
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Listing 14-1: A documentation comment for a function
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Here, we give a description of what the `add_one` function does, start a
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section with the heading `Examples`, and then provide code that demonstrates
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how to use the `add_one` function. We can generate the HTML documentation from
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this documentation comment by running `cargo doc`. This command runs the
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`rustdoc` tool distributed with Rust and puts the generated HTML documentation
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in the *target/doc* directory.
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For convenience, running `cargo doc --open` will build the HTML for your
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current crate’s documentation (as well as the documentation for all of your
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crate’s dependencies) and open the result in a web browser. Navigate to the
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`add_one` function and you’ll see how the text in the documentation comments is
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rendered, as shown in Figure 14-1.
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Figure 14-1: HTML documentation for the `add_one` function
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#### Commonly Used Sections
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We used the `# Examples` Markdown heading in Listing 14-1 to create a section
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in the HTML with the title “Examples.” Here are some other sections that crate
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authors commonly use in their documentation:
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* **Panics**: The scenarios in which the function being documented could panic.
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Callers of the function who don’t want their programs to panic should make sure
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they don’t call the function in these situations.
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* **Errors**: If the function returns a `Result`, describing the kinds of
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errors that might occur and what conditions might cause those errors to be
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returned can be helpful to callers so they can write code to handle the
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different kinds of errors in different ways.
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* **Safety**: If the function is `unsafe` to call (we discuss unsafety in
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Chapter 19), there should be a section explaining why the function is unsafe
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and covering the invariants that the function expects callers to uphold.
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Most documentation comments don’t need all of these sections, but this is a
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good checklist to remind you of the aspects of your code users will be
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interested in knowing about.
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#### Documentation Comments as Tests
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Adding example code blocks in your documentation comments can help demonstrate
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how to use your library, and doing so has an additional bonus: running `cargo
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test` will run the code examples in your documentation as tests! Nothing is
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better than documentation with examples. But nothing is worse than examples
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that don’t work because the code has changed since the documentation was
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written. If we run `cargo test` with the documentation for the `add_one`
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function from Listing 14-1, we will see a section in the test results that
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looks like this:
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```
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Doc-tests my_crate
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running 1 test
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test src/lib.rs - add_one (line 5) ... ok
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test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0
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filtered out; finished in 0.27s
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```
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Now, if we change either the function or the example so the `assert_eq!` in the
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example panics and run `cargo test` again, we’ll see that the doc tests catch
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that the example and the code are out of sync with each other!
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#### Commenting Contained Items
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The doc comment `//!` adds documentation to the item that *contains* the
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comments rather than to the items *following* the comments. We typically use
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these doc comments inside the crate root file (*src/lib.rs* by convention) or
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inside a module to document the crate or the module as a whole.
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For example, to add documentation that describes the purpose of the `my_crate`
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crate that contains the `add_one` function, we add documentation comments that
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start with `//!` to the beginning of the *src/lib.rs* file, as shown in Listing
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14-2.
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Filename: src/lib.rs
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```
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//! # My Crate
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//!
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//! `my_crate` is a collection of utilities to make performing
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//! certain calculations more convenient.
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/// Adds one to the number given.
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--snip--
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```
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Listing 14-2: Documentation for the `my_crate` crate as a whole
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Notice there isn’t any code after the last line that begins with `//!`. Because
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we started the comments with `//!` instead of `///`, we’re documenting the item
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that contains this comment rather than an item that follows this comment. In
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this case, that item is the *src/lib.rs* file, which is the crate root. These
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comments describe the entire crate.
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When we run `cargo doc --open`, these comments will display on the front page
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of the documentation for `my_crate` above the list of public items in the
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crate, as shown in Figure 14-2.
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Figure 14-2: Rendered documentation for `my_crate`, including the comment
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describing the crate as a whole
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Documentation comments within items are useful for describing crates and
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modules especially. Use them to explain the overall purpose of the container to
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help your users understand the crate’s organization.
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### Exporting a Convenient Public API with pub use
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The structure of your public API is a major consideration when publishing a
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crate. People who use your crate are less familiar with the structure than you
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are and might have difficulty finding the pieces they want to use if your crate
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has a large module hierarchy.
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In Chapter 7, we covered how to make items public using the `pub` keyword, and
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how to bring items into a scope with the `use` keyword. However, the structure
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that makes sense to you while you’re developing a crate might not be very
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convenient for your users. You might want to organize your structs in a
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hierarchy containing multiple levels, but then people who want to use a type
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you’ve defined deep in the hierarchy might have trouble finding out that type
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exists. They might also be annoyed at having to enter `use`
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`my_crate::`some_module`::`another_module`::`UsefulType`;` rather than `use`
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`my_crate::`UsefulType`;`.
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The good news is that if the structure *isn’t* convenient for others to use
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from another library, you don’t have to rearrange your internal organization:
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instead, you can re-export items to make a public structure that’s different
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from your private structure by using `pub use`. *Re-exporting* takes a public
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item in one location and makes it public in another location, as if it were
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defined in the other location instead.
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For example, say we made a library named `art` for modeling artistic concepts.
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Within this library are two modules: a `kinds` module containing two enums
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named `PrimaryColor` and `SecondaryColor` and a `utils` module containing a
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function named `mix`, as shown in Listing 14-3.
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Filename: src/lib.rs
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```
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//! # Art
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//!
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//! A library for modeling artistic concepts.
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pub mod kinds {
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/// The primary colors according to the RYB color model.
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pub enum PrimaryColor {
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Red,
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Yellow,
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Blue,
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}
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/// The secondary colors according to the RYB color model.
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pub enum SecondaryColor {
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Orange,
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Green,
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Purple,
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}
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}
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pub mod utils {
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use crate::kinds::*;
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/// Combines two primary colors in equal amounts to create
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/// a secondary color.
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pub fn mix(
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c1: PrimaryColor,
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c2: PrimaryColor,
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) -> SecondaryColor {
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--snip--
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}
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}
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```
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Listing 14-3: An `art` library with items organized into `kinds` and `utils`
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modules
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Figure 14-3 shows what the front page of the documentation for this crate
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generated by `cargo doc` would look like.
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Figure 14-3: Front page of the documentation for `art` that lists the `kinds`
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and `utils` modules
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Note that the `PrimaryColor` and `SecondaryColor` types aren’t listed on the
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front page, nor is the `mix` function. We have to click `kinds` and `utils` to
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see them.
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Another crate that depends on this library would need `use` statements that
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bring the items from `art` into scope, specifying the module structure that’s
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currently defined. Listing 14-4 shows an example of a crate that uses the
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`PrimaryColor` and `mix` items from the `art` crate.
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Filename: src/main.rs
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```
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use art::kinds::PrimaryColor;
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use art::utils::mix;
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fn main() {
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let red = PrimaryColor::Red;
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let yellow = PrimaryColor::Yellow;
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mix(red, yellow);
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}
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```
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Listing 14-4: A crate using the `art` crate’s items with its internal structure
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exported
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The author of the code in Listing 14-4, which uses the `art` crate, had to
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figure out that `PrimaryColor` is in the `kinds` module and `mix` is in the
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`utils` module. The module structure of the `art` crate is more relevant to
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developers working on the `art` crate than to those using it. The internal
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structure doesn’t contain any useful information for someone trying to
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understand how to use the `art` crate, but rather causes confusion because
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developers who use it have to figure out where to look, and must specify the
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module names in the `use` statements.
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To remove the internal organization from the public API, we can modify the
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`art` crate code in Listing 14-3 to add `pub use` statements to re-export the
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items at the top level, as shown in Listing 14-5.
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Filename: src/lib.rs
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```
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//! # Art
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//!
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//! A library for modeling artistic concepts.
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pub use self::kinds::PrimaryColor;
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pub use self::kinds::SecondaryColor;
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pub use self::utils::mix;
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pub mod kinds {
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--snip--
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}
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pub mod utils {
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--snip--
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}
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```
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Listing 14-5: Adding `pub use` statements to re-export items
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The API documentation that `cargo doc` generates for this crate will now list
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and link re-exports on the front page, as shown in Figure 14-4, making the
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`PrimaryColor` and `SecondaryColor` types and the `mix` function easier to find.
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Figure 14-4: The front page of the documentation for `art` that lists the
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re-exports
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The `art` crate users can still see and use the internal structure from Listing
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14-3 as demonstrated in Listing 14-4, or they can use the more convenient
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structure in Listing 14-5, as shown in Listing 14-6.
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Filename: src/main.rs
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```
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use art::mix;
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use art::PrimaryColor;
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fn main() {
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--snip--
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}
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```
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Listing 14-6: A program using the re-exported items from the `art` crate
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|
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In cases where there are many nested modules, re-exporting the types at the top
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level with `pub use` can make a significant difference in the experience of
|
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people who use the crate. Another common use of `pub use` is to re-export
|
||
definitions of a dependency in the current crate to make that crate’s
|
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definitions part of your crate’s public API.
|
||
|
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Creating a useful public API structure is more of an art than a science, and
|
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you can iterate to find the API that works best for your users. Choosing `pub
|
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use` gives you flexibility in how you structure your crate internally and
|
||
decouples that internal structure from what you present to your users. Look at
|
||
some of the code of crates you’ve installed to see if their internal structure
|
||
differs from their public API.
|
||
|
||
### Setting Up a Crates.io Account
|
||
|
||
Before you can publish any crates, you need to create an account on
|
||
*https://crates.io* and get an API token. To do so, visit the home page at
|
||
*https://crates.io* and log in via a GitHub account. (The GitHub account is
|
||
currently a requirement, but the site might support other ways of creating an
|
||
account in the future.) Once you’re logged in, visit your account settings at
|
||
*https://crates.io/me* and retrieve your API key. Then run the `cargo login`
|
||
command with your API key, like this:
|
||
|
||
```
|
||
$ cargo login abcdefghijklmnopqrstuvwxyz012345
|
||
```
|
||
|
||
This command will inform Cargo of your API token and store it locally in
|
||
*~/.cargo/credentials*. Note that this token is a *secret*: do not share it
|
||
with anyone else. If you do share it with anyone for any reason, you should
|
||
revoke it and generate a new token on *https://crates.io*.
|
||
|
||
### Adding Metadata to a New Crate
|
||
|
||
Let’s say you have a crate you want to publish. Before publishing, you’ll need
|
||
to add some metadata in the `[package]` section of the crate’s *Cargo.toml*
|
||
file.
|
||
|
||
Your crate will need a unique name. While you’re working on a crate locally,
|
||
you can name a crate whatever you’d like. However, crate names on
|
||
*https://crates.io* are allocated on a first-come, first-served basis. Once a
|
||
crate name is taken, no one else can publish a crate with that name. Before
|
||
attempting to publish a crate, search for the name you want to use. If the name
|
||
has been used, you will need to find another name and edit the `name` field in
|
||
the *Cargo.toml* file under the `[package]` section to use the new name for
|
||
publishing, like so:
|
||
|
||
Filename: Cargo.toml
|
||
|
||
```
|
||
[package]
|
||
name = "guessing_game"
|
||
```
|
||
|
||
Even if you’ve chosen a unique name, when you run `cargo publish` to publish
|
||
the crate at this point, you’ll get a warning and then an error:
|
||
|
||
```
|
||
$ cargo publish
|
||
Updating crates.io index
|
||
warning: manifest has no description, license, license-file, documentation,
|
||
homepage or repository.
|
||
See https://doc.rust-lang.org/cargo/reference/manifest.html#package-metadata
|
||
for more info.
|
||
--snip--
|
||
error: failed to publish to registry at https://crates.io
|
||
|
||
Caused by:
|
||
the remote server responded with an error: missing or empty metadata fields:
|
||
description, license. Please see https://doc.rust-
|
||
lang.org/cargo/reference/manifest.html for how to upload metadata
|
||
```
|
||
|
||
This results in an error because you’re missing some crucial information: a
|
||
description and license are required so people will know what your crate does
|
||
and under what terms they can use it. In *Cargo.toml*, add a description that’s
|
||
just a sentence or two, because it will appear with your crate in search
|
||
results. For the `license` field, you need to give a *license identifier
|
||
value*. The Linux Foundation’s Software Package Data Exchange (SPDX) at
|
||
*http://spdx.org/licenses* lists the identifiers you can use for this value.
|
||
For example, to specify that you’ve licensed your crate using the MIT License,
|
||
add the `MIT` identifier:
|
||
|
||
Filename: Cargo.toml
|
||
|
||
```
|
||
[package]
|
||
name = "guessing_game"
|
||
license = "MIT"
|
||
```
|
||
|
||
If you want to use a license that doesn’t appear in the SPDX, you need to place
|
||
the text of that license in a file, include the file in your project, and then
|
||
use `license-file` to specify the name of that file instead of using the
|
||
`license` key.
|
||
|
||
Guidance on which license is appropriate for your project is beyond the scope
|
||
of this book. Many people in the Rust community license their projects in the
|
||
same way as Rust by using a dual license of `MIT OR Apache-2.0`. This practice
|
||
demonstrates that you can also specify multiple license identifiers separated
|
||
by `OR` to have multiple licenses for your project.
|
||
|
||
With a unique name, the version, your description, and a license added, the
|
||
*Cargo.toml* file for a project that is ready to publish might look like this:
|
||
|
||
Filename: Cargo.toml
|
||
|
||
```
|
||
[package]
|
||
name = "guessing_game"
|
||
version = "0.1.0"
|
||
edition = "2021"
|
||
description = "A fun game where you guess what number the
|
||
computer has chosen."
|
||
license = "MIT OR Apache-2.0"
|
||
|
||
[dependencies]
|
||
```
|
||
|
||
Cargo’s documentation at *https://doc.rust-lang.org/cargo* describes other
|
||
metadata you can specify to ensure that others can discover and use your crate
|
||
more easily.
|
||
|
||
### Publishing to Crates.io
|
||
|
||
Now that you’ve created an account, saved your API token, chosen a name for
|
||
your crate, and specified the required metadata, you’re ready to publish!
|
||
Publishing a crate uploads a specific version to *https://crates.io* for others
|
||
to use.
|
||
|
||
Be careful, because a publish is *permanent*. The version can never be
|
||
overwritten, and the code cannot be deleted. One major goal of Crates.io is to
|
||
act as a permanent archive of code so that builds of all projects that depend
|
||
on crates from *https://crates.io* will continue to work. Allowing version
|
||
deletions would make fulfilling that goal impossible. However, there is no
|
||
limit to the number of crate versions you can publish.
|
||
|
||
Run the `cargo publish` command again. It should succeed now:
|
||
|
||
```
|
||
$ cargo publish
|
||
Updating crates.io index
|
||
Packaging guessing_game v0.1.0 (file:///projects/guessing_game)
|
||
Verifying guessing_game v0.1.0 (file:///projects/guessing_game)
|
||
Compiling guessing_game v0.1.0
|
||
(file:///projects/guessing_game/target/package/guessing_game-0.1.0)
|
||
Finished dev [unoptimized + debuginfo] target(s) in 0.19s
|
||
Uploading guessing_game v0.1.0 (file:///projects/guessing_game)
|
||
```
|
||
|
||
Congratulations! You’ve now shared your code with the Rust community, and
|
||
anyone can easily add your crate as a dependency of their project.
|
||
|
||
### Publishing a New Version of an Existing Crate
|
||
|
||
When you’ve made changes to your crate and are ready to release a new version,
|
||
you change the `version` value specified in your *Cargo.toml* file and
|
||
republish. Use the Semantic Versioning rules at *http://semver.org* to decide
|
||
what an appropriate next version number is, based on the kinds of changes
|
||
you’ve made. Then run `cargo publish` to upload the new version.
|
||
|
||
### Deprecating Versions from Crates.io with cargo yank
|
||
|
||
Although you can’t remove previous versions of a crate, you can prevent any
|
||
future projects from adding them as a new dependency. This is useful when a
|
||
crate version is broken for one reason or another. In such situations, Cargo
|
||
supports yanking a crate version.
|
||
|
||
*Yanking* a version prevents new projects from depending on that version while
|
||
allowing all existing projects that depend on it to continue. Essentially, a
|
||
yank means that all projects with a *Cargo.lock* will not break, and any future
|
||
*Cargo.lock* files generated will not use the yanked version.
|
||
|
||
To yank a version of a crate, in the directory of the crate that you’ve
|
||
previously published, run `cargo yank` and specify which version you want to
|
||
yank. For example, if we’ve published a crate named `guessing_game` version
|
||
1.0.1 and we want to yank it, in the project directory for `guessing_game` we’d
|
||
run:
|
||
|
||
```
|
||
$ cargo yank --vers 1.0.1
|
||
Updating crates.io index
|
||
Yank guessing_game@1.0.1
|
||
```
|
||
|
||
By adding `--undo` to the command, you can also undo a yank and allow projects
|
||
to start depending on a version again:
|
||
|
||
```
|
||
$ cargo yank --vers 1.0.1 --undo
|
||
Updating crates.io index
|
||
Unyank guessing_game@1.0.1
|
||
```
|
||
|
||
A yank *does not* delete any code. It cannot, for example, delete accidentally
|
||
uploaded secrets. If that happens, you must reset those secrets immediately.
|
||
|
||
## Cargo Workspaces
|
||
|
||
In Chapter 12, we built a package that included a binary crate and a library
|
||
crate. As your project develops, you might find that the library crate
|
||
continues to get bigger and you want to split your package further into
|
||
multiple library crates. Cargo offers a feature called *workspaces* that can
|
||
help manage multiple related packages that are developed in tandem.
|
||
|
||
### Creating a Workspace
|
||
|
||
A *workspace* is a set of packages that share the same *Cargo.lock* and output
|
||
directory. Let’s make a project using a workspace—we’ll use trivial code so we
|
||
can concentrate on the structure of the workspace. There are multiple ways to
|
||
structure a workspace, so we’ll just show one common way. We’ll have a
|
||
workspace containing a binary and two libraries. The binary, which will provide
|
||
the main functionality, will depend on the two libraries. One library will
|
||
provide an `add_one` function and the other library an `add_two` function.
|
||
These three crates will be part of the same workspace. We’ll start by creating
|
||
a new directory for the workspace:
|
||
|
||
```
|
||
$ mkdir add
|
||
$ cd add
|
||
```
|
||
|
||
Next, in the *add* directory, we create the *Cargo.toml* file that will
|
||
configure the entire workspace. This file won’t have a `[package]` section.
|
||
Instead, it will start with a `[workspace]` section that will allow us to add
|
||
members to the workspace by specifying the path to the package with our binary
|
||
crate; in this case, that path is *adder*:
|
||
|
||
Filename: Cargo.toml
|
||
|
||
```
|
||
[workspace]
|
||
|
||
members = [
|
||
"adder",
|
||
]
|
||
```
|
||
|
||
Next, we’ll create the `adder` binary crate by running `cargo new` within the
|
||
*add* directory:
|
||
|
||
```
|
||
$ cargo new adder
|
||
Created binary (application) `adder` package
|
||
```
|
||
|
||
At this point, we can build the workspace by running `cargo build`. The files
|
||
in your *add* directory should look like this:
|
||
|
||
```
|
||
├── Cargo.lock
|
||
├── Cargo.toml
|
||
├── adder
|
||
│ ├── Cargo.toml
|
||
│ └── src
|
||
│ └── main.rs
|
||
└── target
|
||
```
|
||
|
||
The workspace has one *target* directory at the top level that the compiled
|
||
artifacts will be placed into; the `adder` package doesn’t have its own
|
||
*target* directory. Even if we were to run `cargo build` from inside the
|
||
*adder* directory, the compiled artifacts would still end up in *add/target*
|
||
rather than *add/adder/target*. Cargo structures the *target* directory in a
|
||
workspace like this because the crates in a workspace are meant to depend on
|
||
each other. If each crate had its own *target* directory, each crate would have
|
||
to recompile each of the other crates in the workspace to place the artifacts
|
||
in its own *target* directory. By sharing one *target* directory, the crates
|
||
can avoid unnecessary rebuilding.
|
||
|
||
### Creating the Second Package in the Workspace
|
||
|
||
Next, let’s create another member package in the workspace and call it
|
||
`add_one`. Change the top-level *Cargo.toml* to specify the *add_one* path in
|
||
the `members` list:
|
||
|
||
Filename: Cargo.toml
|
||
|
||
```
|
||
[workspace]
|
||
|
||
members = [
|
||
"adder",
|
||
"add_one",
|
||
]
|
||
```
|
||
|
||
Then generate a new library crate named `add_one`:
|
||
|
||
```
|
||
$ cargo new add_one --lib
|
||
Created library `add_one` package
|
||
```
|
||
|
||
Your *add* directory should now have these directories and files:
|
||
|
||
```
|
||
├── Cargo.lock
|
||
├── Cargo.toml
|
||
├── add_one
|
||
│ ├── Cargo.toml
|
||
│ └── src
|
||
│ └── lib.rs
|
||
├── adder
|
||
│ ├── Cargo.toml
|
||
│ └── src
|
||
│ └── main.rs
|
||
└── target
|
||
```
|
||
|
||
In the *add_one/src/lib.rs* file, let’s add an `add_one` function:
|
||
|
||
Filename: add_one/src/lib.rs
|
||
|
||
```
|
||
pub fn add_one(x: i32) -> i32 {
|
||
x + 1
|
||
}
|
||
```
|
||
|
||
Now we can have the `adder` package with our binary depend on the `add_one`
|
||
package that has our library. First we’ll need to add a path dependency on
|
||
`add_one` to *adder/Cargo.toml*:
|
||
|
||
Filename: adder/Cargo.toml
|
||
|
||
```
|
||
[dependencies]
|
||
add_one = { path = "../add_one" }
|
||
```
|
||
|
||
Cargo doesn’t assume that crates in a workspace will depend on each other, so
|
||
we need to be explicit about the dependency relationships.
|
||
|
||
Next, let’s use the `add_one` function (from the `add_one` crate) in the
|
||
`adder` crate. Open the *adder/src/main.rs* file and add a `use` line at the
|
||
top to bring the new `add_one` library crate into scope. Then change the `main`
|
||
function to call the `add_one` function, as in Listing 14-7.
|
||
|
||
Filename: adder/src/main.rs
|
||
|
||
```
|
||
use add_one;
|
||
|
||
fn main() {
|
||
let num = 10;
|
||
println!(
|
||
"Hello, world! {num} plus one is {}!",
|
||
add_one::add_one(num)
|
||
);
|
||
}
|
||
```
|
||
|
||
Listing 14-7: Using the `add_one` library crate from the `adder` crate
|
||
|
||
Let’s build the workspace by running `cargo build` in the top-level *add*
|
||
directory!
|
||
|
||
```
|
||
$ cargo build
|
||
Compiling add_one v0.1.0 (file:///projects/add/add_one)
|
||
Compiling adder v0.1.0 (file:///projects/add/adder)
|
||
Finished dev [unoptimized + debuginfo] target(s) in 0.68s
|
||
```
|
||
|
||
To run the binary crate from the *add* directory, we can specify which package
|
||
in the workspace we want to run by using the `-p` argument and the package name
|
||
with `cargo run`:
|
||
|
||
```
|
||
$ cargo run -p adder
|
||
Finished dev [unoptimized + debuginfo] target(s) in 0.0s
|
||
Running `target/debug/adder`
|
||
Hello, world! 10 plus one is 11!
|
||
```
|
||
|
||
This runs the code in *adder/src/main.rs*, which depends on the `add_one` crate.
|
||
|
||
#### Depending on an External Package in a Workspace
|
||
|
||
Notice that the workspace has only one *Cargo.lock* file at the top level,
|
||
rather than having a *Cargo.lock* in each crate’s directory. This ensures that
|
||
all crates are using the same version of all dependencies. If we add the `rand`
|
||
package to the *adder/Cargo.toml* and *add_one/Cargo.toml* files, Cargo will
|
||
resolve both of those to one version of `rand` and record that in the one
|
||
*Cargo.lock*. Making all crates in the workspace use the same dependencies
|
||
means the crates will always be compatible with each other. Let’s add the
|
||
`rand` crate to the `[dependencies]` section in the *add_one/Cargo.toml* file
|
||
so we can use the `rand` crate in the `add_one` crate:
|
||
|
||
Filename: add_one/Cargo.toml
|
||
|
||
```
|
||
[dependencies]
|
||
rand = "0.8.5"
|
||
```
|
||
|
||
We can now add `use rand;` to the *add_one/src/lib.rs* file, and building the
|
||
whole workspace by running `cargo build` in the *add* directory will bring in
|
||
and compile the `rand` crate. We will get one warning because we aren’t
|
||
referring to the `rand` we brought into scope:
|
||
|
||
```
|
||
$ cargo build
|
||
Updating crates.io index
|
||
Downloaded rand v0.8.5
|
||
--snip--
|
||
Compiling rand v0.8.5
|
||
Compiling add_one v0.1.0 (file:///projects/add/add_one)
|
||
Compiling adder v0.1.0 (file:///projects/add/adder)
|
||
Finished dev [unoptimized + debuginfo] target(s) in 10.18s
|
||
```
|
||
|
||
The top-level *Cargo.lock* now contains information about the dependency of
|
||
`add_one` on `rand`. However, even though `rand` is used somewhere in the
|
||
workspace, we can’t use it in other crates in the workspace unless we add
|
||
`rand` to their *Cargo.toml* files as well. For example, if we add `use rand;`
|
||
to the *adder/src/main.rs* file for the `adder` package, we’ll get an error:
|
||
|
||
```
|
||
$ cargo build
|
||
--snip--
|
||
Compiling adder v0.1.0 (file:///projects/add/adder)
|
||
error[E0432]: unresolved import `rand`
|
||
--> adder/src/main.rs:2:5
|
||
|
|
||
2 | use rand;
|
||
| ^^^^ no external crate `rand`
|
||
```
|
||
|
||
To fix this, edit the *Cargo.toml* file for the `adder` package and indicate
|
||
that `rand` is a dependency for it as well. Building the `adder` package will
|
||
add `rand` to the list of dependencies for `adder` in *Cargo.lock*, but no
|
||
additional copies of `rand` will be downloaded. Cargo has ensured that every
|
||
crate in every package in the workspace using the `rand` package will be using
|
||
the same version, saving us space and ensuring that the crates in the workspace
|
||
will be compatible with each other.
|
||
|
||
#### Adding a Test to a Workspace
|
||
|
||
For another enhancement, let’s add a test of the `add_one::add_one` function
|
||
within the `add_one` crate:
|
||
|
||
Filename: add_one/src/lib.rs
|
||
|
||
```
|
||
pub fn add_one(x: i32) -> i32 {
|
||
x + 1
|
||
}
|
||
|
||
#[cfg(test)]
|
||
mod tests {
|
||
use super::*;
|
||
|
||
#[test]
|
||
fn it_works() {
|
||
assert_eq!(3, add_one(2));
|
||
}
|
||
}
|
||
```
|
||
|
||
Now run `cargo test` in the top-level *add* directory. Running `cargo test` in
|
||
a workspace structured like this one will run the tests for all the crates in
|
||
the workspace:
|
||
|
||
```
|
||
$ cargo test
|
||
Compiling add_one v0.1.0 (file:///projects/add/add_one)
|
||
Compiling adder v0.1.0 (file:///projects/add/adder)
|
||
Finished test [unoptimized + debuginfo] target(s) in 0.27s
|
||
Running unittests src/lib.rs (target/debug/deps/add_one-f0253159197f7841)
|
||
|
||
running 1 test
|
||
test tests::it_works ... ok
|
||
|
||
test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out;
|
||
finished in 0.00s
|
||
|
||
Running unittests src/main.rs (target/debug/deps/adder-49979ff40686fa8e)
|
||
|
||
running 0 tests
|
||
|
||
test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out;
|
||
finished in 0.00s
|
||
|
||
Doc-tests add_one
|
||
|
||
running 0 tests
|
||
|
||
test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out;
|
||
finished in 0.00s
|
||
```
|
||
|
||
The first section of the output shows that the `it_works` test in the `add_one`
|
||
crate passed. The next section shows that zero tests were found in the `adder`
|
||
crate, and then the last section shows zero documentation tests were found in
|
||
the `add_one` crate.
|
||
|
||
We can also run tests for one particular crate in a workspace from the
|
||
top-level directory by using the `-p` flag and specifying the name of the crate
|
||
we want to test:
|
||
|
||
```
|
||
$ cargo test -p add_one
|
||
Finished test [unoptimized + debuginfo] target(s) in 0.00s
|
||
Running unittests src/lib.rs (target/debug/deps/add_one-b3235fea9a156f74)
|
||
|
||
running 1 test
|
||
test tests::it_works ... ok
|
||
|
||
test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out;
|
||
finished in 0.00s
|
||
|
||
Doc-tests add_one
|
||
|
||
running 0 tests
|
||
|
||
test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out;
|
||
finished in 0.00s
|
||
```
|
||
|
||
This output shows `cargo test` only ran the tests for the `add_one` crate and
|
||
didn’t run the `adder` crate tests.
|
||
|
||
If you publish the crates in the workspace to *https://crates.io*, each crate
|
||
in the workspace will need to be published separately. Like `cargo test`, we
|
||
can publish a particular crate in our workspace by using the `-p` flag and
|
||
specifying the name of the crate we want to publish.
|
||
|
||
For additional practice, add an `add_two` crate to this workspace in a similar
|
||
way as the `add_one` crate!
|
||
|
||
As your project grows, consider using a workspace: it provides
|
||
easier-to-understand, smaller, individual components than one big blob of code.
|
||
Furthermore, keeping the crates in a workspace can make coordination between
|
||
crates easier if they are often changed at the same time.
|
||
|
||
## Installing Binaries with cargo install
|
||
|
||
The `cargo install` command allows you to install and use binary crates
|
||
locally. This isn’t intended to replace system packages; it’s meant to be a
|
||
convenient way for Rust developers to install tools that others have shared on
|
||
*https://crates.io*. Note that you can only install packages that have binary
|
||
targets. A *binary target* is the runnable program that is created if the crate
|
||
has a *src/main.rs* file or another file specified as a binary, as opposed to a
|
||
library target that isn’t runnable on its own but is suitable for including
|
||
within other programs. Usually, crates have information in the *README* file
|
||
about whether a crate is a library, has a binary target, or both.
|
||
|
||
All binaries installed with `cargo install` are stored in the installation
|
||
root’s *bin* folder. If you installed Rust using *rustup.rs* and don’t have any
|
||
custom configurations, this directory will be *$HOME/.cargo/bin*. Ensure that
|
||
directory is in your `$PATH` to be able to run programs you’ve installed with
|
||
`cargo install`.
|
||
|
||
For example, in Chapter 12 we mentioned that there’s a Rust implementation of
|
||
the `grep` tool called `ripgrep` for searching files. To install `ripgrep`, we
|
||
can run the following:
|
||
|
||
```
|
||
$ cargo install ripgrep
|
||
Updating crates.io index
|
||
Downloaded ripgrep v13.0.0
|
||
Downloaded 1 crate (243.3 KB) in 0.88s
|
||
Installing ripgrep v13.0.0
|
||
--snip--
|
||
Compiling ripgrep v13.0.0
|
||
Finished release [optimized + debuginfo] target(s) in 3m 10s
|
||
Installing ~/.cargo/bin/rg
|
||
Installed package `ripgrep v13.0.0` (executable `rg`)
|
||
```
|
||
|
||
The second-to-last line of the output shows the location and the name of the
|
||
installed binary, which in the case of `ripgrep` is `rg`. As long as the
|
||
installation directory is in your `$PATH`, as mentioned previously, you can
|
||
then run `rg --help` and start using a faster, Rustier tool for searching files!
|
||
|
||
## Extending Cargo with Custom Commands
|
||
|
||
Cargo is designed so you can extend it with new subcommands without having to
|
||
modify it. If a binary in your `$PATH` is named `cargo-something`, you can run
|
||
it as if it were a Cargo subcommand by running `cargo something`. Custom
|
||
commands like this are also listed when you run `cargo --list`. Being able to
|
||
use `cargo install` to install extensions and then run them just like the
|
||
built-in Cargo tools is a super-convenient benefit of Cargo’s design!
|
||
|
||
## Summary
|
||
|
||
Sharing code with Cargo and *https://crates.io* is part of what makes the Rust
|
||
ecosystem useful for many different tasks. Rust’s standard library is small and
|
||
stable, but crates are easy to share, use, and improve on a timeline different
|
||
from that of the language. Don’t be shy about sharing code that’s useful to you
|
||
on *https://crates.io*; it’s likely that it will be useful to someone else as
|
||
well!
|
||
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