reduce-similarities

name	reduce-similarities
description	Detects duplicated Rust code with the dev-shell similarity-rs CLI. Use when reviewing .rs files for repeated functions, impl methods, or parallel struct and enum definitions, or before extracting a shared helper.
argument-hint	[path] [--threshold 0.85] [--print]
allowed-tools	Bash(similarity-rs *) Read Grep Glob
paths	**/*.rs

Rust Code Similarity Detection

similarity-rs comes from the Nix dev shell (similarity in nix/dev-shell.nix); prefix it with direnv exec . from outside the shell. TypeScript duplication belongs to the typescript and ast-grep skills.

Run it over $ARGUMENTS, or over . when none was given. Functions and type definitions are separate passes, so a default run silently misses parallel structs and enums:

similarity-rs . --threshold 0.85 --min-lines 5
similarity-rs . --threshold 0.85 --experimental-types

--print shows the matching snippets and similarity-rs --help has the rest; --skip-test is worth adding when fixture-shaped test functions drown out the real findings.

Triage

A score is a starting point, not a verdict. Usually worth refactoring:

• 100% matches: extract a shared function or generic.
• 95-100% across different types: generic function with trait bounds.
• Duplicate impl methods on several types: trait with default implementations.
• 85-95% match arms or error handling: shared helper or macro.
• Parallel structs with identical fields: shared base or generic struct.

Usually left alone: short new() constructors, simple From/Into impls, and anything a derive would generate.

Report each surviving candidate as a concrete before/after shape, not as a list of scores.