similarity-rs

similarity-rs 0.5 — Rust duplication detection

Tool status: Beta — not production-tested per the upstream README. Evaluate findings manually before acting.

When to use this skill

Antipattern triggers (act before writing code):

• About to write a utility function — grep the codebase first; it may already exist.
• Caught yourself thinking "I'll just inline this here."
• Planning to copy-paste-modify an existing function with small changes.
• Adding a new enum or struct that may overlap with an existing one.
• Two Plugin setups that share large blocks of boilerplate.
• Similar Bevy systems that differ only in their Query filter component.
• Repeated commands.spawn((Mesh3d(...), MeshMaterial3d(...), ...)) patterns that belong in a Bundle.

Tool-integration triggers (run the check):

• Before committing: verify you haven't introduced cross-file duplication.
• During a cleanup sprint: identify consolidation candidates.
• Setting up a pre-commit hook or GitHub Actions gate.
• Adjusting -t/--threshold or --min-lines for a noisy or too-quiet run.

Canonical workflow

The pattern is: search first → write minimally → run the check.

# 1. Search before writing — check whether the helper already exists
rg "fn <verb>"               # e.g., rg "fn normalize" to find existing helpers
cargo doc --open --package <dep>  # inventory what your deps already provide

# 2. Write only what's missing.

# 3. Before committing, check for accidental duplication
cargo install similarity-rs   # one-time install
similarity-rs ./src            # scan the src tree

# 4. If --cross-file output is needed (catches LLM's most common antipattern)
similarity-rs --cross-file ./src

# 5. Tighten or loosen if needed (see references/tuning.md)
similarity-rs -t 0.85 -m 5 --cross-file --skip-test ./src

Consult cargo doc --open for every dependency before reaching for a one-off helper. LLMs reproduce functions from stdlib, itertools, or an already-declared crate dep more often than from thin air.