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rationalize-deps

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Analyze Cargo.toml dependencies and attempt to remove unused features to reduce compile times and binary size

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Rationalize Dependencies

This skill analyzes Cargo.toml dependencies to identify and remove unused features.

Overview

Many crates enable features by default that may not be needed. This skill:

  1. Identifies dependencies with default features enabled
  2. Tests if default-features = false works
  3. Identifies which specific features are actually needed
  4. Verifies compilation after changes

Step 1: Identify the target

Ask the user which crate(s) to analyze:

  • A specific crate name (e.g., "tokio", "serde")
  • A specific workspace member (e.g., "quickwit-search")
  • "all" to scan the entire workspace

Step 2: Analyze current dependencies

For the workspace Cargo.toml (quickwit/Cargo.toml), list dependencies that:

  • Do NOT have default-features = false
  • Have default features that might be unnecessary

Run: cargo tree -p <crate> -f "{p} {f}" --edges features to see what features are actually used.

Step 3: For each candidate dependency

3a: Check the crate's default features

Look up the crate on crates.io or check its Cargo.toml to understand:

  • What features are enabled by default
  • What each feature provides

Use: cargo metadata --format-version=1 | jq '.packages[] | select(.name == "<crate>") | .features'

3b: Try disabling default features

Modify the dependency in quickwit/Cargo.toml:

From:

some-crate = { version = "1.0" }

To:

some-crate = { version = "1.0", default-features = false }

3c: Run cargo check

Run: cargo check --workspace (or target specific packages for faster feedback)

If compilation fails:

  1. Read the error messages to identify which features are needed
  2. Add only the required features explicitly: 
    some-crate = { version = "1.0", default-features = false, features = ["needed-feature"] }
  3. Re-run cargo check

3d: Binary search for minimal features

If there are many default features, use binary search:

  1. Start with no features
  2. If it fails, add half the default features
  3. Continue until you find the minimal set

Step 4: Document findings

For each dependency analyzed, report:

  • Original configuration
  • New configuration (if changed)
  • Features that were removed
  • Any features that are required

Step 5: Verify full build

After all changes, run:

cargo check --workspace --all-targets
cargo test --workspace --no-run

Common Patterns

Serde

Often only needs derive:

serde = { version = "1.0", default-features = false, features = ["derive", "std"] }

Tokio

Identify which runtime features are actually used:

tokio = { version = "1.0", default-features = false, features = ["rt-multi-thread", "macros", "sync"] }

Reqwest

Often doesn't need all TLS backends:

reqwest = { version = "0.11", default-features = false, features = ["rustls-tls", "json"] }

Rollback

If changes cause issues:

git checkout quickwit/Cargo.toml
cargo check --workspace

Tips

  • Start with large crates that have many default features (tokio, reqwest, hyper)
  • Use cargo bloat --crates to identify large dependencies
  • Check cargo tree -d for duplicate dependencies that might indicate feature conflicts
  • Some features are needed only for tests - consider using [dev-dependencies] features