SplitRS 🦀✂️

A production-ready Rust refactoring tool that intelligently splits large files into maintainable modules

SplitRS uses AST-based analysis to automatically refactor large Rust source files (>1000 lines) into well-organized, compilable modules. It handles complex generics, async functions, Arc/Mutex patterns, and automatically generates correct imports and visibility modifiers.

✨ Features

Core Refactoring

• 🎯 AST-Based Refactoring: Uses syn for accurate Rust parsing
• 🧠 Intelligent Method Clustering: Groups related methods using call graph analysis
• 📦 Auto-Generated Imports: Context-aware use statements with proper paths
• 🔒 Visibility Inference: Automatically applies pub(super), pub(crate), or pub
• 🚀 Complex Type Support: Handles generics, async, Arc/Mutex, nested types
• ⚡ Fast: Processes 1600+ line files in <1 second
• ✅ Production-Tested: Successfully refactored 10,000+ lines of real code

Advanced Features (v0.2.0+)

• ⚙️ Configuration Files: .splitrs.toml support for project-specific settings
• 🎭 Trait Implementation Support: Automatic separation of trait impls into dedicated modules
• 🔗 Type Alias Resolution: Intelligent handling of type aliases in import generation
• 🔍 Circular Dependency Detection: DFS-based cycle detection with Graphviz export
• 👀 Enhanced Preview Mode: Beautiful formatted preview with statistics before refactoring
• 💬 Interactive Mode: Confirmation prompts before file generation
• 🔄 Automatic Rollback Support: Backup creation for safe refactoring
• 📝 Smart Documentation: Auto-generated module docs with trait listings

📦 Installation

cargo install splitrs

Or build from source:

git clone https://github.com/cool-japan/splitrs
cd splitrs
cargo build --release

🚀 Quick Start

Basic Usage

# Split a large file into modules
splitrs --input src/large_file.rs --output src/large_file/

# Preview what will be created (no files written)
splitrs --input src/large_file.rs --output src/large_file/ --dry-run

# Interactive mode with confirmation
splitrs --input src/large_file.rs --output src/large_file/ --interactive

Recommended Usage (with impl block splitting)

splitrs \
  --input src/large_file.rs \
  --output src/large_file/ \
  --split-impl-blocks \
  --max-impl-lines 200

Using Configuration Files

Create a .splitrs.toml in your project root:

[splitrs]
max_lines = 1000
max_impl_lines = 500
split_impl_blocks = true

[naming]
type_module_suffix = "_type"
impl_module_suffix = "_impl"

[output]
preserve_comments = true
format_output = true

Then simply run:

splitrs --input src/large_file.rs --output src/large_file/

📖 Examples

Example 1: Trait Implementations

SplitRS automatically detects and separates trait implementations:

Input: user.rs

pub struct User {
    pub name: String,
    pub age: u32,
}

impl User {
    pub fn new(name: String, age: u32) -> Self { /* ... */ }
}

impl Debug for User { /* ... */ }
impl Display for User { /* ... */ }
impl Clone for User { /* ... */ }
impl Default for User { /* ... */ }

Command:

splitrs --input user.rs --output user/ --dry-run

Output:

user/
├── types.rs         # struct User definition + inherent impl
├── user_traits.rs   # All trait implementations (Debug, Display, Clone, Default)
└── mod.rs          # Module organization

Generated user_traits.rs:

//! # User - Trait Implementations
//!
//! This module contains trait implementations for `User`.
//!
//! ## Implemented Traits
//!
//! - `Debug`
//! - `Display`
//! - `Clone`
//! - `Default`
//!
//! 🤖 Generated with [SplitRS](https://github.com/cool-japan/splitrs)

use super::types::User;

impl Debug for User { /* ... */ }
impl Display for User { /* ... */ }
impl Clone for User { /* ... */ }
impl Default for User { /* ... */ }

Example 2: Basic Refactoring

Input: connection_pool.rs (1660 lines)

pub struct ConnectionPool<T> {
    connections: Arc<Mutex<Vec<T>>>,
    config: PoolConfig,
    // ... 50 fields
}

impl<T: Clone + Send + Sync> ConnectionPool<T> {
    pub fn new(config: PoolConfig) -> Self { ... }
    pub async fn acquire(&self) -> Result<T> { ... }
    pub async fn release(&self, conn: T) -> Result<()> { ... }
    // ... 80 methods
}

Command:

splitrs --input connection_pool.rs --output connection_pool/ --split-impl-blocks

Output: 25 well-organized modules

connection_pool/
├── mod.rs                          # Module organization & re-exports
├── connectionpool_type.rs          # Type definition with proper visibility
├── connectionpool_new_group.rs     # Constructor methods
├── connectionpool_acquire_group.rs # Connection acquisition
├── connectionpool_release_group.rs # Connection release
└── ... (20 more focused modules)

Example 3: Preview Mode

Get detailed information before refactoring:

splitrs --input examples/trait_impl_example.rs --output /tmp/preview -n

Output:

============================================================
DRY RUN - Preview Mode
============================================================

📊 Statistics:
  Original file: 82 lines
  Total modules to create: 4

📁 Module Structure:
  📄 product_traits.rs (2 trait impls)
  📄 user_traits.rs (4 trait impls)
  📄 types.rs (2 types)
  📄 functions.rs (1 items)

💾 Files that would be created:
  📁 /tmp/preview/
    📄 product_traits.rs
    📄 user_traits.rs
    📄 types.rs
    📄 functions.rs
    📄 mod.rs

============================================================
✓ Preview complete - no files were created
============================================================

Example 4: Complex Types

SplitRS correctly handles complex Rust patterns:

// Input
pub struct Cache<K, V>
where
    K: Hash + Eq + Clone,
    V: Clone + Send + Sync + 'static,
{
    data: Arc<RwLock<HashMap<K, V>>>,
    eviction: EvictionPolicy,
}

// Output (auto-generated)
// cache_type.rs
use std::collections::HashMap;
use std::sync::{Arc, RwLock};

pub struct Cache<K, V>
where
    K: Hash + Eq + Clone,
    V: Clone + Send + Sync + 'static,
{
    pub(super) data: Arc<RwLock<HashMap<K, V>>>,
    pub(super) eviction: EvictionPolicy,
}

// cache_insert_group.rs
use super::cache_type::Cache;
use std::collections::HashMap;

impl<K, V> Cache<K, V>
where
    K: Hash + Eq + Clone,
    V: Clone + Send + Sync + 'static,
{
    pub async fn insert(&mut self, key: K, value: V) -> Result<()> {
        // ... implementation
    }
}

🎛️ Command-Line Options

Option	Short	Description	Default
--input <FILE>	-i	Input Rust source file (required)	-
--output <DIR>	-o	Output directory for modules (required)	-
--max-lines <N>	-m	Maximum lines per module	1000
--split-impl-blocks		Split large impl blocks into method groups	false
--max-impl-lines <N>		Maximum lines per impl block before splitting	500
--dry-run	-n	Preview without creating files	false
--interactive	-I	Prompt for confirmation before creating files	false
--config <FILE>	-c	Path to configuration file	.splitrs.toml

Configuration File Options

When using a .splitrs.toml file, you can configure:

[splitrs] section:

• max_lines - Maximum lines per module
• max_impl_lines - Maximum lines per impl block
• split_impl_blocks - Enable impl block splitting

[naming] section:

• type_module_suffix - Suffix for type modules (default: "_type")
• impl_module_suffix - Suffix for impl modules (default: "_impl")
• use_snake_case - Use snake_case for module names (default: true)

[output] section:

• module_doc_template - Template for module documentation
• preserve_comments - Preserve original comments (default: true)
• format_output - Format with prettyplease (default: true)

Command-line arguments always override configuration file settings.

🏗️ How It Works

SplitRS uses a multi-stage analysis pipeline:

1. AST Parsing: Parse input file with syn
2. Scope Analysis: Determine organization strategy and visibility
3. Method Clustering: Build call graph and cluster related methods
4. Type Extraction: Extract types from fields for import generation
5. Module Generation: Generate well-organized modules with correct imports
6. Code Formatting: Format output with prettyplease

Organization Strategies

Inline - Keep impl blocks with type definition:

typename_module.rs
  ├── struct TypeName { ... }
  └── impl TypeName { ... }

Submodule - Split type and impl blocks (recommended for large files):

typename_type.rs       # Type definition
typename_new_group.rs  # Constructor methods
typename_getters.rs    # Getter methods
mod.rs                 # Module organization

Wrapper - Wrap in parent module:

typename/
  ├── type.rs
  ├── methods.rs
  └── mod.rs

📊 Performance

Tested on real-world codebases:

File Size	Lines	Time	Modules Generated
Small	500-1000	<100ms	3-5
Medium	1000-1500	<500ms	5-12
Large	1500-2000	<1s	10-25
Very Large	2000+	<2s	25-40

🧪 Testing

SplitRS includes comprehensive tests:

# Run all tests
cargo test

# Test on example files
cargo run -- --input examples/large_struct.rs --output /tmp/test_output

📚 Documentation

API Documentation (docs.rs)

Full API documentation is available at docs.rs/splitrs.

Generate documentation locally:

# Generate and open documentation
cargo doc --no-deps --open

# Generate documentation for all features
cargo doc --all-features --no-deps

Module Structure

The codebase is organized into these main modules:

• main.rs - CLI interface, file analysis, and module generation
• config.rs - Configuration file parsing and management (.splitrs.toml)
• method_analyzer.rs - Method dependency analysis and grouping
• import_analyzer.rs - Type usage tracking and import generation
• scope_analyzer.rs - Module scope analysis and visibility inference
• dependency_analyzer.rs - Circular dependency detection and graph visualization

Key Types and Traits

Core Types:

• FileAnalyzer - Main analyzer for processing Rust files
• TypeInfo - Information about a Rust type and its implementations
• Module - Represents a generated module
• Config - Configuration loaded from .splitrs.toml

Analysis Types:

• ImplBlockAnalyzer - Analyzes impl blocks for splitting
• MethodGroup - Groups related methods together
• ImportAnalyzer - Tracks type usage and generates imports
• DependencyGraph - Detects circular dependencies

📚 Use Cases

When to Use SplitRS

✅ Perfect for:

• Files >1000 lines with large impl blocks
• Monolithic modules that need organization
• Legacy code refactoring
• Improving code maintainability

⚠️ Consider Carefully:

• Files with circular dependencies (will generate modules but may need manual fixes)
• Files with heavy macro usage (basic support, may need manual review)

❌ Not Recommended:

• Files <500 lines (probably already well-organized)
• Files with complex conditional compilation (#[cfg])

🔧 Integration

CI/CD Pipeline

# .github/workflows/refactor.yml
name: Auto-refactor
on:
  workflow_dispatch:
    inputs:
      file:
        description: 'File to refactor'
        required: true

jobs:
  refactor:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3
      - uses: actions-rs/toolchain@v1
        with:
          toolchain: stable
      - run: cargo install splitrs
      - run: |
          splitrs --input ${{ github.event.inputs.file }} \
                  --output $(dirname ${{ github.event.inputs.file }})/refactored \
                  --split-impl-blocks
      - uses: peter-evans/create-pull-request@v5
        with:
          title: "Refactor: Split ${{ github.event.inputs.file }}"

🤝 Contributing

Contributions are welcome! Please see CONTRIBUTING.md for guidelines.

Development Setup

git clone https://github.com/cool-japan/splitrs
cd splitrs
cargo build
cargo test

Implemented Features (v0.2.0)

• ✅ Configuration file support (.splitrs.toml)
• ✅ Trait implementation separation
• ✅ Type alias resolution
• ✅ Circular dependency detection (DFS + DOT export)
• ✅ Enhanced preview mode with statistics
• ✅ Interactive confirmation mode
• ✅ Automatic rollback support
• ✅ Smart documentation generation

Roadmap to v1.0

Current status: 85% production-ready

Next features (v0.3.0):

• Incremental refactoring (detect existing splits)
• Custom naming strategies (plugin system)
• Integration test generation
• Performance benchmarking suite

Future enhancements (v0.4.0+):

• Macro expansion support
• Workspace-level refactoring
• LSP integration
• Editor plugins (VS Code, IntelliJ)

📄 License

Licensed under either of:

• Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

🙏 Acknowledgments

• Built with syn for Rust parsing
• Formatted with prettyplease
• Developed during the OxiRS refactoring project (32,398 lines refactored)

📞 Resources & Support

• 📖 API Documentation: docs.rs/splitrs
• 📦 Crate: crates.io/crates/splitrs
• 💻 Source Code: github.com/cool-japan/splitrs
• 🐛 Issue Tracker: github.com/cool-japan/splitrs/issues
• 💬 Discussions: github.com/cool-japan/splitrs/discussions

Getting Help

1. Check the docs: Read the API documentation and examples
2. Search issues: Check if your question is already answered in issues
3. Ask questions: Start a discussion
4. Report bugs: Open an issue with a reproducible example

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