Rust Workspaces

In Rust, workspaces are a way to organize multiple packages (crates) into a single project with a shared Cargo.lock and output directory (target/). This is especially useful for large projects with multiple components, such as libraries and binaries, that need to share code or build settings.

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🧱 What Is a Workspace?

A workspace is a set of one or more member crates (packages) managed together by Cargo.

• It has a single root Cargo.toml (called the workspace manifest) that defines the workspace.
• Each member crate has its own Cargo.toml.
• All members share the same Cargo.lock and target/ directory.

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📁 Basic Structure

Here’s an example of a typical workspace layout:

my_workspace/
├── Cargo.toml            # Workspace root (workspace manifest)
├── members/
│   ├── my_lib/
│   │   └── Cargo.toml    # A library crate
│   └── my_app/
│       └── Cargo.toml    # A binary crate
└── target/               # Shared build output directory

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🛠️ Workspace Root Cargo.toml

[workspace]
members = [
    "members/my_lib",
    "members/my_app"
]

You can also use globs:

[workspace]
members = ["members/*"]

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📦 Member Crates

Each member crate still has its own Cargo.toml, like this for my_lib:

[package]
name = "my_lib"
version = "0.1.0"
edition = "2021"

[dependencies]

And for my_app:

[package]
name = "my_app"
version = "0.1.0"
edition = "2021"

[dependencies]

my_lib = { path = “../my_lib” } # Use the workspace member

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✅ Benefits of Workspaces

• Single build directory (target/) saves build time.
• Shared Cargo.lock ensures consistent dependency versions across all crates.
• Ideal for monorepos: libraries, apps, plugins in one repo.
• Easier testing: you can test the whole workspace with cargo test.

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🚀 Common Commands

• cargo build (in workspace root) builds all members.
• cargo build -p my_app builds just one member.
• cargo test, cargo check, etc. also work similarly.

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🔒 Optional Members

You can have crates in your repository that are not part of the workspace using exclude:

[workspace]
members = ["members/*"]
exclude = ["members/experimental_crate"]

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🧪 Example Use Case

A real-world example could be:

• core – a reusable library.
• cli – a command-line interface binary.
• web – a web server binary.
• tools/gen_docs – an internal documentation tool.

All living in one repo, built and tested together.

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