The Cargo check Command

Introduction to cargo check

In Rust development, managing dependencies, compiling code, and ensuring everything works correctly can be quite complex. The Rust package manager, Cargo, provides various commands to simplify these tasks. One of these essential commands is cargo check.

The cargo check command is used to quickly check your code for errors without producing an executable. It is a fast way to ensure that your code compiles and all dependencies are correct, but it skips the actual linking process, which is the step that generates the final executable or library.

Why Use cargo check?

  1. Speed: Since cargo check stops before the linking step, it is significantly faster than running cargo build. This speed advantage is particularly noticeable in larger projects or when making frequent changes during development.

  2. Error Detection: It helps catch compilation errors early. By frequently running cargo check, you can ensure that your codebase remains in a compile-ready state.

  3. Resource Efficiency: Because it skips the linking step, cargo check uses fewer system resources, making it a more efficient way to iterate on your code.

Get cargo check Help

To learn more about the cargo check command and its available options, you can access its manual page directly from the command line. This built-in help provides detailed information on how to use the command and the various flags that can be applied. To view the help manual, run the following command in your terminal:

cargo help check

This command will display a comprehensive guide, including:

  • Synopsis: A brief summary of the command syntax.
  • Description: An overview of what the command does.
  • Options: Detailed descriptions of the available options and flags you can use with cargo check.

Here is a truncated output of the previous command:

CARGO-CHECK(1)                        General Commands Manual                        CARGO-CHECK(1)

NAME
       cargo-check — Check the current package

SYNOPSIS
       cargo check [options]

DESCRIPTION
       Check a local package and all of its dependencies for errors. This will essentially compile
       the packages without performing the final step of code generation, which is faster than
       running cargo build. The compiler will save metadata files to disk so that future runs will
       reuse them if the source has not been modified. Some diagnostics and errors are only emitted
       during code generation, so they inherently won’t be reported with cargo check.

OPTIONS
   Package Selection
       By default, when no package selection options are given, the packages selected depend on the
       selected manifest file (based on the current working directory if --manifest-path is not
       given). If the manifest is the root of a workspace then the workspaces default members are
       selected, otherwise only the package defined by the manifest will be selected.

       The default members of a workspace can be set explicitly with the workspace.default-members
       key in the root manifest. If this is not set, a virtual workspace will include all workspace
:

How to Use cargo check

Using cargo check is straightforward. Simply navigate to the root of your Rust project and run the following command:

cargo check
  • This command will analyze your project, checking all the code and dependencies for errors.

Example Usage

Let's consider a simple Rust project to illustrate how cargo check works. Assume you we have created a rust application named simple_app using cargo new simple_app. To check this application, you would run:

cargo check

If there are no errors, you'll see output similar to:

Checking simple_app v0.1.0 (/your/app/path/simple_app)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.62s

If there are errors, cargo check will output them, allowing you to correct issues before they become more significant problems.

For example, if you have a syntax error in main.rs, the output might look like this:

Checking simple_app v0.1.0 (/app/path/simple_app)
error: cannot find macro `prinln` in this scope
   --> src/main.rs:2:5
    |
2   |     prinln!("Hello, world!");
    |     ^^^^^^ help: a macro with a similar name exists: `println`
    |
   ::: /Users/daas/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/src/rust/library/std/src/macros.rs:138:1
    |
138 | macro_rules! println {
    | -------------------- similarly named macro `println` defined here

error: could not compile `simple_app` (bin "simple_app") due to 1 previous error

notice how rust compiler points to the error, and also suggests some solutions.

This feedback allows you to correct issues before they become more significant problems. By frequently running cargo check, you can ensure that your codebase remains free of compilation errors as you develop your project.

Advanced Usage

cargo check can be customized using various flags to fit different development needs. Some of the most commonly used options include:

--release

This will check the code in release mode, which applies optimizations and is closer to what the final build will look like. This is useful for catching issues that may only appear in optimized builds.

cargo check --release

--all-targets

Check all targets in the project, including tests, examples, and benchmarks, not just the default binary. This ensures that every part of the project is free of errors.

cargo check --all-targets

--workspace

Check all packages in the workspace. This is useful for multi-package projects where you want to ensure that the entire workspace is error-free.

cargo check --workspace

--package <SPEC>

Check only the specified package within a workspace. Replace <SPEC> with the package name. This allows for targeted checking when working in large workspaces.

cargo check --package <SPEC>

--lib

Check only the library target. This is useful if your project contains both binary and library targets, and you only want to check the library code.

cargo check --lib

--bin <NAME>

Check only the specified binary. Replace <NAME> with the name of the binary target you want to check. This is useful for projects with multiple binaries.

cargo check --bin <NAME>

--examples

Check all example targets. This is useful for ensuring that example code provided with your library is also free of errors.

cargo check --examples

--tests

Check all test targets. This ensures that your test code is also free of errors, helping maintain test quality and reliability.

cargo check --tests

--benches

Check all benchmark targets. This is useful for projects that include benchmarks, ensuring that benchmarking code is also error-free.

cargo check --benches

--all-features

Check the code with all features enabled. This ensures that your code works with every optional feature you provide.

cargo check --all-features

--no-default-features

Check the code with default features disabled. This is useful for ensuring that your code can compile without relying on default features.

cargo check --no-default-features

--features <FEATURES>

Check the code with a specific set of features enabled. Replace <FEATURES> with a comma-separated list of feature names. This allows for testing specific feature combinations.

cargo check --features <FEATURES>

Using these options of cargo check command will enable us to customize the check process to suit different parts of the development workflow, and this will ensure a thorough and efficient error checking across the entire project.

You won't need to memorize these options, refer to the help page whenever you need to.

Best Practices for Using cargo check

  • Frequent Checks: Utilize cargo check regularly during development to identify and resolve errors early. This proactive approach helps maintain a robust codebase and minimizes the time spent on debugging.

  • Continuous Integration: Incorporate cargo check into your Continuous Integration (CI) pipeline. By doing so, you ensure that every commit is validated for compilation errors, maintaining the integrity of your codebase.

  • Complement with cargo build: Use cargo check for swift feedback on code changes during development. For more comprehensive validation, including linking and executing tests, use cargo build or cargo test. This combination ensures both quick iteration and thorough verification of your code.

Summary

The cargo check command is an essential tool for Rust developers, offering a quick and efficient method to ensure code is free of compilation errors without the overhead of generating an executable.

  • By integrating cargo check into your regular development workflo, you can
    • Save time
    • Identify errors early
    • Maintain a smooth and efficient project development process.