add-rust-dependency
Guide for safely adding a new Rust crate dependency in torrust-tracker, starting from the latest stable crates.io version, minimizing features, documenting version rationale, and validating with cargo machete and repository quality gates. Use when introducing a new dependency, selecting a crate version, or justifying why an older version is required.
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- Guide for safely adding a new Rust crate dependency in torrust-tracker, starting from the latest stable crates.io version, minimizing features, documenting version rationale, and validating with cargo machete and repository quality gates. Use when introducing a new dependency, selecting a crate version, or justifying why an older version is required.
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- {"author":"torrust","version":"1.0","semantic-links":{"related-artifacts":["AGENTS.md",".github/agents/implementer.agent.md",".github/skills/dev/maintenance/update-dependencies/SKILL.md"]}}
# Adding a Rust Dependency
Use this workflow when introducing a new crate to `Cargo.toml`.
## Goal
Add only necessary dependencies, prefer the latest stable version, and keep the resulting change
reviewable, justified, and maintainable.
## Skill Links
- `AGENTS.md`
- `.github/agents/implementer.agent.md`
- `.github/skills/dev/maintenance/update-dependencies/SKILL.md`
## Workflow
### Step 1: Confirm a new dependency is necessary
Before adding a crate, check whether the need can be met by:
- the Rust standard library,
- an existing workspace dependency,
- a small local implementation with lower long-term cost.
If one of these options is sufficient, do not add a new crate.
### Step 2: Check the latest stable version first
Identify the latest stable crates.io version before choosing a version.
```bash
cargo search <crate-name> --limit 1
```
Start from the latest stable version by default.
If you must choose an older version, document the reason in the PR/issue spec and, when useful,
in a nearby code comment.
### Step 3: Choose the minimal feature set
Prefer `default-features = false` when appropriate and enable only required features.
```toml
[dependencies]
example-crate = { version = "<latest-stable>", default-features = false, features = ["needed-feature"] }
```
Avoid broad feature enables without a concrete need.
### Step 4: Apply and verify
After editing `Cargo.toml`/`Cargo.lock`:
```bash
cargo update -p <crate-name>
cargo machete
./contrib/dev-tools/git/hooks/pre-commit.sh --format=json
```
If the run fails and more diagnostics are needed, retry with:
```bash
./contrib/dev-tools/git/hooks/pre-commit.sh --format=text --verbosity=verbose
```
If checks fail, resolve issues or revert the dependency addition.
### Step 5: Document rationale
In commit/PR/issue notes, record:
- why this crate is needed,
- why alternatives were not selected,
- why a non-latest version is used (if applicable),
- any noteworthy feature-flag choices.
## Constraints
- Do not introduce a dependency without checking latest stable first.
- Do not keep a non-latest version without explicit rationale.
- Do not add dependency bloat when existing dependencies already solve the problem.
- Do not skip `cargo machete` and pre-commit validation.
## Related Skills
- Update existing dependencies: `.github/skills/dev/maintenance/update-dependencies/SKILL.md`
- Commit workflow: `.github/skills/dev/git-workflow/commit-changes/SKILL.md`
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