Cargo dependency management in Rust - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Cargo.toml dependency version resolution?

Given the following Cargo.toml snippet, what version of serde will Cargo use?

[dependencies]
serde = "^1.0.100"
serde_derive = "1.0.104"

Assume no other dependencies affect serde.

A 1.0.100

B 1.0.104

C 1.0.99

D 1.0.105

💡 Hint

Check how Cargo resolves compatible versions with caret requirements.

Caret requirements like ^1.0.100 allow versions >=1.0.100 and <2.0.0. Cargo picks the highest compatible version. Since serde_derive requires 1.0.104, Cargo uses 1.0.104 for both.

🧠 Conceptual

intermediate

Which Cargo command updates dependencies to the latest compatible versions?

You want to update your Rust project's dependencies to the latest versions allowed by your Cargo.toml constraints. Which command should you run?

A cargo update

B cargo refresh

C cargo build --update

D cargo upgrade

💡 Hint

Think about the official Cargo command that updates the lock file.

cargo update updates the Cargo.lock file to the latest versions allowed by Cargo.toml. cargo upgrade is from an external tool, not built-in.

🔧 Debug

advanced

Why does this Cargo build fail with a version conflict error?

Consider a Rust project with these dependencies in Cargo.toml:

[dependencies]
foo = "1.2.0"
bar = "2.0.0"

Both foo and bar depend on different incompatible versions of baz. What is the most likely cause of the build failure?

A The <code>baz</code> crate is unpublished and cannot be downloaded.

B The <code>Cargo.toml</code> file is missing a <code>[workspace]</code> section.

C Cargo cannot unify incompatible versions of <code>baz</code> required by <code>foo</code> and <code>bar</code>.

D The Rust compiler version is too old to build <code>foo</code> and <code>bar</code>.

💡 Hint

Think about how Cargo handles multiple versions of the same crate.

Cargo tries to unify dependencies to a single version. If foo and bar require incompatible versions of baz, Cargo cannot resolve the conflict, causing a build failure.

📝 Syntax

advanced

Which Cargo.toml snippet correctly specifies a git dependency?

You want to depend on a crate from a Git repository instead of crates.io. Which snippet is correct?

A

[dependencies]
mycrate = { git = "https://github.com/user/mycrate.git", branch = "main" }

B

[dependencies]
mycrate = git: "https://github.com/user/mycrate.git", branch = "main"

C

[dependencies]
mycrate = { url = "https://github.com/user/mycrate.git", branch = "main" }

D

[dependencies]
mycrate = { git = "https://github.com/user/mycrate.git" branch = "main" }

💡 Hint

Check the correct key name and syntax for specifying git dependencies in Cargo.toml.

The correct syntax uses git as the key inside braces with commas separating fields. Option A is correct. Option A uses invalid syntax, C uses wrong key url, and A misses a comma.

🚀 Application

expert

How many dependencies will Cargo build with this workspace setup?

Given a Cargo workspace with two crates:

[workspace]
members = ["crate_a", "crate_b"]

# crate_a/Cargo.toml
[dependencies]
serde = "1.0"

# crate_b/Cargo.toml
[dependencies]
serde = "1.0"
regex = "1.5"

How many unique dependencies will Cargo compile for the entire workspace?

A 1

B 4

C 3

D 2

💡 Hint

Consider shared dependencies and unique dependencies across workspace members.

Both crates depend on serde "1.0" (compatible, so compiled once). crate_b also depends on regex. Thus, two unique dependencies: serde and regex. Workspace members are packages, not dependencies.