reduce-similarities

name	reduce-similarities
description	Detect duplicate Rust code using AST-based similarity analysis. Use when working with .rs files and looking for code duplication or refactoring opportunities.
argument-hint	[path] [--threshold 0.85] [--print]
allowed-tools	Bash(similarity-rs *) Read Grep Glob
paths	**/*.rs

Rust Code Similarity Detection

What to do

Run similarity-rs on the target Rust project to detect duplicate functions, struct/enum definitions, and impl methods, then analyze results and propose refactoring.

If similarity-rs is not installed:

similarity-rs

# or

direnv exec . similarity-rs

Step 1: Run similarity analysis

similarity-rs $ARGUMENTS

If no arguments given:

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

For struct/enum similarity:

similarity-rs . --threshold 0.85 --experimental-types

Step 2: Analyze results

High-priority

• 100% similarity: Exact duplicates -> extract shared function or use generics
• 95-100%: Same algorithm on different types -> generic function with trait bounds
• Duplicate impl methods: Same logic across types -> trait with default implementation

Medium-priority

• 85-95%: Similar match arms or error handling -> macro or shared helper
• Parallel struct definitions: Identical fields -> shared base or generic struct

Acceptable

• Short new() constructors with field initialization
• Simple From/Into implementations
• Derive-equivalent implementations

Step 3: Propose refactoring

For each high-priority pair, show before/after code with Rust idioms.

Key Options

Option	Description
--threshold <0-1>	Similarity threshold (default: 0.85)
--min-lines <n>	Skip functions shorter than n lines (default: 3)
--min-tokens <n>	Skip functions with fewer AST nodes
--print	Show actual code snippets
--experimental-types	Enable struct/enum similarity detection
--filter-function <name>	Filter by function name
--fail-on-duplicates	Exit code 1 if duplicates found

Common Rust refactoring patterns

• Type-specific functions -> generic fn<T: Trait> with trait bounds
• Duplicate impl blocks across types -> trait with default methods
• Repeated match patterns -> macro_rules! or helper function
• Parallel X/Y/Z functions -> enum parameter or tuple-based abstraction
• Similar error handling -> shared Result combinator or ? chain