rusty-cpp

Bringing Rust's safety to C++ through:

1. Static Borrow Checker - Compile-time ownership and lifetime analysis via rusty-cpp-checker. 2. Safe Types - Box<T>, RefCell<T>, Vec<T>, HashMap<K,V>, etc. 3. Rust Idioms - Send/Sync traits, RAII guards, type-state patterns, Result<T,E>/Option<T>, etc.

1. Borrow Checking and Lifetime Analysis

🎯 Vision

This project aims to catch memory safety issues at compile-time by applying Rust's proven ownership model to C++ code. It helps prevent common bugs like use-after-move, double-free, and dangling references before they reach production.

Though C++ is flexible enough to mimic Rust's idioms in many ways, implementing a borrow-checking without modifying the compiler system appears to be impossible, as analyzed in this document.

We provide rusty-cpp-checker, a standalone static analyzer that enforces Rust-like ownership and borrowing rules for C++ code, bringing memory safety guarantees to existing C++ codebases without runtime overhead. rusty-cpp-checker does not bringing any new grammar into c++. Everything works through simple annoations such as adding // @safe enables safety checking on a function.

Example

Here's a simple demonstration of how const reference borrowing works:

// @safe
void demonstrate_const_ref_borrowing() {
    int value = 42;
    
    // Multiple const references are allowed (immutable borrows)
    const int& ref1 = value;  // First immutable borrow - OK
    const int& ref2 = value;  // Second immutable borrow - OK  
    const int& ref3 = value;  // Third immutable borrow - OK
    
    // All can be used simultaneously to read the value
    int sum = ref1 + ref2 + ref3;  // OK - reading through const refs
}

// @safe
void demonstrate_const_ref_violation() {
    int value = 42;
    
    const int& const_ref = value;  // Immutable borrow - OK
    int& mut_ref = value;          // ERROR: Cannot have mutable borrow when immutable exists
    
    // This would violate the guarantee that const_ref won't see unexpected changes
    mut_ref = 100;  // If allowed, const_ref would suddenly see value 100
}

Analysis Output:

Rusty C++ Checker
Analyzing: example.cpp
✗ Found 2 violation(s) in example.cpp:
Cannot create mutable reference to 'value': already immutably borrowed
Cannot create mutable borrow 'mut_ref': 'value' is already borrowed by 'const_ref'

✨ Features

Core Capabilities

🔄 Borrow Checking: Enforces Rust's borrowing rules (multiple readers XOR single writer)
🔒 Ownership Tracking: Ensures single ownership of resources with move semantics
⏳ Lifetime Analysis: Validates that references don't outlive their data

Detected Issues

Use-after-move violations
Multiple mutable borrows
Dangling references
Lifetime constraint violations
RAII violations
Data races (through borrow checking)

📦 Installation

Quick Install (Recommended)

The easiest way to install rusty-cpp is using our install script, which automatically detects your OS and installs all dependencies:

# One-liner install (detects OS, installs deps, builds from source)
curl -sSL https://raw.githubusercontent.com/shuaimu/rusty-cpp/main/install.sh | bash

Or clone and run locally:

git clone https://github.com/shuaimu/rusty-cpp
cd rusty-cpp
./install.sh

Supported platforms:

macOS (via Homebrew)
Ubuntu/Debian (apt)
Fedora (dnf)
CentOS/RHEL 8+ (dnf)
Arch Linux (pacman)

⚠️ Build Requirements (Manual Installation)

If you prefer manual installation, this tool requires the following native dependencies to be installed before building from source or installing via cargo:

Rust: 1.70+ (for building the analyzer)
LLVM/Clang: 16+ (for parsing C++ - required by clang-sys)
Z3: 4.8+ (for constraint solving - required by z3-sys)

Note: These dependencies must be installed system-wide before running cargo install rusty-cpp or building from source. The build will fail without them.

Installing from crates.io

Once you have the prerequisites installed:

# macOS: Set environment variable for Z3
export Z3_SYS_Z3_HEADER=/opt/homebrew/include/z3.h

# Linux: Set environment variable for Z3
export Z3_SYS_Z3_HEADER=/usr/include/z3.h

# Install from crates.io
cargo install rusty-cpp

# The binary will be installed as 'rusty-cpp-checker'
rusty-cpp-checker --help

Building from Source

macOS

# Install dependencies
brew install llvm z3

# Clone the repository
git clone https://github.com/shuaimu/rusty-cpp
cd rusty-cpp

# Build the project
cargo build --release

# Run tests
./run_tests.sh

# Add to PATH (optional)
export PATH="$PATH:$(pwd)/target/release"

Note: The project includes a .cargo/config.toml file that automatically sets the required environment variables for Z3. If you encounter build issues, you may need to adjust the paths in this file based on your system configuration.

Linux (Ubuntu/Debian)

# Install dependencies (LLVM 16+ required)
sudo apt-get update
sudo apt-get install llvm-16-dev libclang-16-dev clang-16 libz3-dev

# Clone and build
git clone https://github.com/shuaimu/rusty-cpp
cd rusty-cpp
cargo build --release

Windows

# Install LLVM from https://releases.llvm.org/
# Install Z3 from https://github.com/Z3Prover/z3/releases
# Set environment variables:
set LIBCLANG_PATH=C:\Program Files\LLVM\lib
set Z3_SYS_Z3_HEADER=C:\z3\include\z3.h

# Build
cargo build --release

🚀 Usage

Basic Usage

# Analyze a single file
rusty-cpp-checker path/to/file.cpp

# Analyze with verbose output
rusty-cpp-checker -vv path/to/file.cpp

# Output in JSON format (for IDE integration)
rusty-cpp-checker --format json path/to/file.cpp

Standalone Binary (No Environment Variables Required)

For release distributions, we provide a standalone binary that doesn't require setting environment variables:

# Build standalone release
./build_release.sh

# Install from distribution
cd dist/rusty-cpp-checker-*/
./install.sh

# Or use directly
./rusty-cpp-checker-standalone file.cpp

See RELEASE.md for details on building and distributing standalone binaries.

Environment Setup (macOS)

For convenience, add these to your shell profile:

# ~/.zshrc or ~/.bashrc
export Z3_SYS_Z3_HEADER=/opt/homebrew/opt/z3/include/z3.h
export DYLD_LIBRARY_PATH=/opt/homebrew/opt/llvm/lib:$DYLD_LIBRARY_PATH

🛡️ Safety System

The borrow checker uses a two-state safety system with automatic header-to-implementation propagation:

Two Safety States

@safe - Functions with full borrow checking and strict calling rules
@unsafe - Everything else (unannotated code is @unsafe by default)

Calling Rules Matrix

Caller → Can Call	@safe	@unsafe
@safe	✅ Yes	❌ No (use `@unsafe` block)
@unsafe	✅ Yes	✅ Yes

Safety Rules Explained

// @safe
void safe_function() {
    // ✅ CAN call other @safe functions
    safe_helper();

    // ❌ CANNOT call @unsafe functions directly
    // unsafe_func();  // ERROR: must use @unsafe block

    // ✅ CAN call @unsafe functions via @unsafe block
    // @unsafe
    {
        unsafe_func();  // OK: in @unsafe block
        std::vector<int> vec;  // OK: STL in @unsafe block
    }

    // ❌ CANNOT do pointer operations (outside @unsafe block)
    // int* ptr = &x;  // ERROR: requires unsafe context
}

// @unsafe (or no annotation - same thing)
void unsafe_function() {
    // ✅ Can call anything and do pointer operations
    safe_function();       // OK: can call safe
    another_unsafe();      // OK: can call unsafe
    int* ptr = nullptr;    // OK: pointer operations allowed
    std::vector<int> vec;  // OK: STL allowed
}

Key Insight: This is a clean two-state model - code is either @safe or @unsafe. Unannotated code is @unsafe by default. To call anything unsafe from @safe code, wrap it in an @unsafe { } block.

Header-to-Implementation Propagation

Safety annotations in headers automatically apply to implementations:

// math.h
// @safe
int calculate(int a, int b);

// @unsafe  
void process_raw_memory(void* ptr);

// math.cpp
#include "math.h"

int calculate(int a, int b) {
    // Automatically @safe from header
    return a + b;
}

void process_raw_memory(void* ptr) {
    // Automatically @unsafe from header
    // Pointer operations allowed
}

STL and External Libraries

By default, all STL and external functions are @unsafe, meaning @safe functions cannot call them directly. You have two options:

Option 1 (Recommended): Use Rusty structures

#include <rusty/box.hpp>
#include <rusty/vec.hpp>

// @safe
void safe_with_rusty() {
    // ✅ OK: Rusty structures are designed for safe code
    rusty::Vec<int> vec;
    vec.push_back(42);  // Safe by design

    rusty::Box<Widget> widget = rusty::Box<Widget>::make(args);
}

Option 2: Use @unsafe blocks for STL

#include <vector>

// @safe
void safe_with_stl() {
    // @unsafe
    {
        std::vector<int> vec;
        vec.push_back(42);  // OK: in @unsafe block
    }
}

Option 3: Mark specific external functions as [safe] via external annotations

If you've audited an external function and want to call it directly from @safe code:

// @external: {
//   my_audited_function: [safe, () -> void]
// }

void my_audited_function();  // External function you've audited

// @safe
void caller() {
    my_audited_function();  // OK: marked [safe] via external annotation
}

See Complete Annotations Guide for comprehensive documentation on all annotation features, including safety, lifetime, and external annotations.

📝 Examples

Example 1: Use After Move

#include <rusty/box.hpp>

// @safe
void bad_code() {
    rusty::Box<int> ptr1 = rusty::Box<int>::make(42);
    rusty::Box<int> ptr2 = std::move(ptr1);

    *ptr1 = 10;  // ERROR: Use after move!
}

Output:

Rusty C++ Checker
Analyzing: example.cpp
✗ Found 1 violation(s) in example.cpp:
Use after move: cannot dereference_write (via operator*) variable 'ptr1' because it has been moved

Example 2: Multiple Mutable Borrows

// @safe
void bad_borrow() {
    int value = 42;
    int& ref1 = value;
    int& ref2 = value;  // ERROR: Cannot borrow as mutable twice
}

Output:

Rusty C++ Checker
Analyzing: example.cpp
✗ Found 3 violation(s) in example.cpp:
Cannot create mutable reference to 'value': already mutably borrowed
Cannot create mutable borrow 'ref1': 'value' is already borrowed by 'ref2'
Cannot create mutable borrow 'ref2': 'value' is already borrowed by 'ref1'

Example 3: Lifetime Violation

// @safe
int& dangling_reference() {
    int local = 42;
    return local;  // ERROR: Returning reference to local variable
}

Output:

Rusty C++ Checker
Analyzing: example.cpp
✗ Found 2 violation(s) in example.cpp:
Safe function 'dangling_reference' returns a reference but has no @lifetime annotation
Cannot return reference to local variable 'local'

🏗️ Architecture

┌─────────────┐     ┌──────────┐     ┌────────┐
│   C++ Code  │────▶│  Parser  │────▶│   IR   │
└─────────────┘     └──────────┘     └────────┘
                          │                │
                    (libclang)              ▼
                                    ┌──────────────┐
┌─────────────┐     ┌──────────┐   │   Analysis   │
│ Diagnostics │◀────│  Solver  │◀──│   Engine     │
└─────────────┘     └──────────┘   └──────────────┘
                         │                │
                       (Z3)        (Ownership/Lifetime)

Components

Parser (src/parser/): Uses libclang to build C++ AST
IR (src/ir/): Ownership-aware intermediate representation
Analysis (src/analysis/): Core borrow checking algorithms
Solver (src/solver/): Z3-based constraint solving for lifetimes
Diagnostics (src/diagnostics/): User-friendly error reporting

🆕 Advanced Features

Using Rusty Structures (Recommended)

RustyCpp provides safe data structures that integrate seamlessly with the borrow checker:

#include <rusty/vec.hpp>
#include <rusty/box.hpp>

// @safe
void example() {
    rusty::Vec<int> vec = {1, 2, 3};
    int& ref = vec[0];     // Borrows &'vec mut
    vec.push_back(4);      // ERROR: Cannot modify vec while ref exists
}

For STL structures, use @unsafe blocks:

#include <vector>

// @safe
void stl_example() {
    // @unsafe
    {
        std::vector<int> vec = {1, 2, 3};
        vec.push_back(4);  // OK: in @unsafe block
    }
}

See Complete Annotations Guide for all annotation features.

External Function Annotations

Annotate third-party functions with safety and lifetime information without modifying their source.

By default, all external functions are @unsafe. You can:

Use @unsafe blocks to call them from @safe code
Mark specific functions as [safe] if you've audited them

// @external: {
//   // Mark as [safe] if you've audited the function
//   my_audited_function: [safe, () -> void]
//
//   // Mark as [unsafe] with lifetime info for documentation
//   strchr: [unsafe, (const char* str, int c) -> const char* where str: 'a, return: 'a]
//   malloc: [unsafe, (size_t size) -> owned void*]
// }

void my_audited_function();

// @safe
void example() {
    my_audited_function();  // OK: marked [safe] via external annotation

    // @unsafe
    {
        const char* text = "hello";
        const char* found = strchr(text, 'e');  // OK: in @unsafe block
    }
}

See Complete Annotations Guide for comprehensive documentation on safety annotations, lifetime annotations, and external annotations.

2. Safe Type Alternatives

RustyCpp provides drop-in replacements for C++ standard library types with built-in safety guarantees:

Available Types

Smart Pointers

rusty::Box<T> - Single ownership pointer with move-only semantics

rusty::Box<Widget> widget = rusty::Box<Widget>::make(42);
auto widget2 = std::move(widget);  // OK: explicit ownership transfer
// widget.get();  // ERROR: use-after-move detected

Interior Mutability

rusty::RefCell<T> - Runtime borrow checking for interior mutability

rusty::RefCell<int> cell(42);
{
    auto ref = cell.borrow();      // Immutable borrow
    // auto mut_ref = cell.borrow_mut();  // ERROR: already borrowed
}
auto mut_ref = cell.borrow_mut();  // OK: previous borrow ended

Containers

rusty::Vec<T> - Dynamic array with iterator invalidation detection

rusty::Vec<int> vec = {1, 2, 3};
auto it = vec.begin();
// vec.push_back(4);  // ERROR: would invalidate iterator

rusty::HashMap<K, V> - Hash map with safe concurrent access patterns
rusty::HashSet<T> - Hash set with ownership semantics
rusty::Rc<T> - Reference counted pointer (single-threaded)
rusty::Arc<T> - Atomic reference counted pointer (thread-safe)

Utility Types

rusty::Option<T> - Explicit handling of optional values
rusty::Result<T, E> - Explicit error handling

Usage

Include the headers:

#include <rusty/box.hpp>
#include <rusty/refcell.hpp>
#include <rusty/vec.hpp>
#include <rusty/hashmap.hpp>

These types are designed to work seamlessly with the borrow checker and enforce Rust's safety guarantees at runtime.

3. Rust Design Idioms

RustyCpp implements key Rust design patterns for safer concurrent programming:

Thread Safety Traits

Send Trait (Explicit Opt-In System)

RustyCpp implements Rust's Send trait using an explicit opt-in system that prevents accidental data races at compile-time:

#include <rusty/sync/mpsc.hpp>

// ✅ Primitives are pre-marked as Send
auto [tx, rx] = rusty::sync::mpsc::channel<int>();

// ✅ Rusty types are Send if their content is Send
auto [tx, rx] = rusty::sync::mpsc::channel<rusty::Arc<int>>();

// ❌ Rc is NOT Send (non-atomic reference counting)
auto [tx, rx] = rusty::sync::mpsc::channel<rusty::Rc<int>>();  // Compile error!

// ❌ Unmarked user types are NOT Send (must explicitly mark)
struct MyType { int value; };
auto [tx, rx] = rusty::sync::mpsc::channel<MyType>();  // Compile error!

How to mark your types as Send:

// Method 1: Static marker (recommended for your types)
class ThreadSafe {
public:
    static constexpr bool is_send = true;  // Explicitly mark as Send
    // ... your thread-safe implementation
};

// Method 2: External specialization (for third-party types)
namespace rusty {
    template<>
    struct is_explicitly_send<ThirdPartyType> : std::true_type {};
}

Key Features:

Safe by default: Types are NOT Send unless explicitly marked
Compositional safety: struct { Rc<T> } is automatically rejected (no Send marker)
Clear errors: Compiler tells you exactly how to fix the issue
No deep analysis needed: Simple marker check at compile-time

Example - Compositional Safety:

// Without marker, this is NOT Send (safe!)
struct ContainsRc {
    rusty::Rc<int> data;  // Non-thread-safe
};

auto [tx, rx] = channel<ContainsRc>();  // ✗ Compile error!
// Error: ContainsRc must be Send (marked explicitly)

// Arc is thread-safe, so use it instead
struct ThreadSafeVersion {
    static constexpr bool is_send = true;
    rusty::Arc<int> data;  // Thread-safe
};

auto [tx, rx] = channel<ThreadSafeVersion>();  // ✓ Works!

MPSC Channel (Multi-Producer Single-Consumer)

Thread-safe message passing channel, identical to Rust's std::sync::mpsc:

#include <rusty/sync/mpsc_lockfree.hpp>  // Lock-free (recommended)
// or
#include <rusty/sync/mpsc.hpp>  // Mutex-based
#include <thread>

using namespace rusty::sync::mpsc::lockfree;  // or ::mutex

void example() {
    // Create channel
    auto [tx, rx] = channel<int>();

    // Clone sender for multiple producers
    auto tx2 = tx.clone();

    // Producer threads
    std::thread t1([tx = std::move(tx)]() mutable {
        tx.send(42);
    });

    std::thread t2([tx2 = std::move(tx2)]() mutable {
        tx2.send(100);
    });

    // Consumer receives from both
    for (int i = 0; i < 2; i++) {
        auto result = rx.recv();
        if (result.is_ok()) {
            int value = result.unwrap();
            std::cout << "Received: " << value << "\n";
        }
    }

    t1.join();
    t2.join();
}

Two Implementations Available:

Lock-Free (mpsc_lockfree.hpp) - Recommended
- 28 M msg/s throughput, 3.3 μs p50 latency
- Batch operations (4x faster under contention)
- Wait-free consumer, lock-free producers
- See User Guide and Developer Guide
Mutex-Based (mpsc.hpp)
- Simple, straightforward implementation
- Lower throughput but easier to understand
- Good for low-frequency communication

Common Features:

Blocking operations: send(), recv()
Non-blocking operations: try_send(), try_recv()
Disconnection detection
Type-safe with Send constraint
Rust-compatible API

Sync Trait

Compile-time marker for types safe to share references between threads:

template<typename T>
concept Sync = /* implementation */;

RAII Guards

Scope-based resource management following Rust's guard pattern:

// MutexGuard automatically unlocks on scope exit
auto guard = mutex.lock();
// ... use protected data ...
// Guard destroyed here, mutex automatically unlocked

Type-State Patterns

Encode state machines in the type system:

struct Unopened {};
struct Opened {};

template<typename State>
class File {
    // Only available when Opened
    std::string read_line() requires std::same_as<State, Opened>;
};

File<Unopened> file("data.txt");
File<Opened> opened = file.open();  // State transition via move
std::string line = opened.read_line();  // OK

Error Handling

Rust-style Result and Option types:

rusty::Result<int, std::string> parse_number(const std::string& str);
rusty::Option<int> find_value(const std::string& key);

// Pattern matching style
auto result = parse_number("42");
if (result.is_ok()) {
    int value = result.unwrap();
} else {
    std::string error = result.unwrap_err();
}

Tips in writing rusty c++

Writing C++ that is easier to debug by adopting principles from Rust.

Being Explicit

Explicitness is one of Rust's core philosophies. It helps prevent errors that arise from overlooking hidden or implicit code behaviors.

No computation in constructors/destructors

Constructors should be limited to initializing member variables and establishing the object's memory layout—nothing more. For additional initialization steps, create a separate Init() function. When member variables require initialization, handle this in the Init() function rather than in the constructor.

Similarly, if you need computation in a destructor (such as setting flags or stopping threads), implement a Destroy() function that must be explicitly called before destruction.

Composition over inheritance

Avoid inheritance whenever possible.

When polymorphism is necessary, limit inheritance to a single layer: an abstract base class and its implementation class. The abstract class should contain no member variables, and all its member functions should be pure virtual (declared with = 0). The implementation class should be marked as final to prevent further inheritance.

Use move and disallow copy assignment/constructor

Except for primitive types, prefer using move instead of copy operations. There are multiple ways to disallow copy constructors; our convention is to inherit from the boost::noncopyable class:

class X: private boost::noncopyable {};

If copy from an object is necessary, implement move constructor and a Clone function:

Object obj1 = move(obj2.Clone()); // move can be omitted because it is already a right value.

Memory Safety, Pointers, and References

No raw pointers

Avoid using raw pointers except when required by system calls, in which case wrap them in a dedicated class.

Use POD types

Try to use POD types if possible. POD means "plain old data". A class is POD if:

No user-defined copy assignment
No virtual functions
No destructor

Incrementally Migrate to Rust (C++/Rust Interop)

Some languages (like D, Zig, and Swift) offer seamless integration with C++. This makes it easier to adopt these languages in existing C++ projects, as you can simply write new code in the chosen language and interact with existing C++ code without friction.

Unfortunately, Rust does not support this level of integration (perhaps intentionally to avoid becoming a secondary option in the C++ ecosystem), as discussed here. Currently, the best approach for C++/Rust interoperability is through the cxx/autocxx crates. This interoperability is implemented as a semi-automated process based on C FFIs (Foreign Function Interfaces) that both C++ and Rust support. However, if your C++ code follows the guidelines in this document, particularly if all types are POD, the interoperability experience can approach the seamless integration offered by other languages (though this remains to be verified).

Closely related projects to watch

Two projects that (attempt to) implement borrow checking in C++ at compile time are Circle C++, and Crubit.

⚠️ Note: This is an experimental tool. Use it at your own discretion.

rusty-cpp 0.1.1

rusty-cpp

1. Borrow Checking and Lifetime Analysis

🎯 Vision

Example

✨ Features

Core Capabilities

Detected Issues

📦 Installation

Quick Install (Recommended)

⚠️ Build Requirements (Manual Installation)

Installing from crates.io

Building from Source

macOS

Linux (Ubuntu/Debian)

Windows

🚀 Usage

Basic Usage

Standalone Binary (No Environment Variables Required)

Environment Setup (macOS)

🛡️ Safety System

Two Safety States

Calling Rules Matrix

Safety Rules Explained

Header-to-Implementation Propagation

STL and External Libraries

📝 Examples

Example 1: Use After Move

Example 2: Multiple Mutable Borrows

Example 3: Lifetime Violation

🏗️ Architecture

Components

🆕 Advanced Features

Using Rusty Structures (Recommended)

External Function Annotations

2. Safe Type Alternatives

Available Types

Smart Pointers

Interior Mutability

Containers

Utility Types

Usage

3. Rust Design Idioms

Thread Safety Traits

Send Trait (Explicit Opt-In System)

MPSC Channel (Multi-Producer Single-Consumer)

Sync Trait

RAII Guards

Type-State Patterns

Error Handling

Tips in writing rusty c++

Being Explicit

No computation in constructors/destructors

Composition over inheritance

Use move and disallow copy assignment/constructor

Memory Safety, Pointers, and References

No raw pointers

Use POD types

Incrementally Migrate to Rust (C++/Rust Interop)

Closely related projects to watch