recvcheck

Go linter that detects mixing pointer and value method receivers.

Why

Mixing pointer and value receivers on the same type creates subtle, hard-to-detect bugs that can cause:

🐛 Data Races

When you copy a struct with a mutex, you copy the mutex state, leading to race conditions:

type RPC struct {
    mu     sync.Mutex  // This is the problem!
    result int
    done   chan struct{}
}

func (rpc *RPC) compute() {
    rpc.mu.Lock()
    defer rpc.mu.Unlock()
    rpc.result = 42
}

func (RPC) version() int {  // Value receiver copies the mutex!
    return 1
}

func main() {
    rpc := &RPC{done: make(chan struct{})}
    go rpc.compute()         // Locks original mutex
    version := rpc.version() // Uses copied mutex - RACE!
    // ...
}

🚨 Silent Bugs

Value receivers create copies, so modifications are lost:

type Counter struct {
    value int
}

func (c *Counter) Increment() { c.value++ }  // pointer receiver
func (c Counter) Reset() { c.value = 0 }     // value receiver - NO EFFECT!

🤔 Developer Confusion

Mixed receivers make code behavior unpredictable and harder to reason about.

✅ The Solution

Consistency is key: Go's official guidance says Don't mix receiver types. Choose either pointers or values for all methods on a type.

recvcheck automatically detects these issues before they reach production.

Installation

# Standalone
go install github.com/raeperd/recvcheck/cmd/recvcheck@latest

# With golangci-lint (recommended)
# Add to .golangci.yml:
linters:
  enable:
    - recvcheck

Usage

recvcheck ./...
# or
golangci-lint run

Output:

main.go:8:1: the methods of "RPC" use pointer receiver and non-pointer receiver

Configuration

# .golangci.yml
linters-settings:
  recvcheck:
    # Disable default exclusions (MarshalJSON, etc.)
    disable-builtin: false
    
    # Custom exclusions
    exclusions:
      - "Server.Shutdown"   # Specific method
      - "*.String"          # All String methods

Default Exclusions

Marshal methods are excluded by default as they commonly use value receivers:

• *.MarshalText, *.MarshalJSON, *.MarshalYAML
• *.MarshalXML, *.MarshalBinary, *.GobEncode

Examples

❌ Bad - Mixed receivers:

func (u *User) SetName(name string) { }  // pointer
func (u User) GetName() string { }       // value - inconsistent!

✅ Good - Consistent receivers:

func (u *User) SetName(name string) { }  // pointer
func (u *User) GetName() string { }      // pointer - consistent!

Contributing

make test  # Run tests
make lint  # Run linter
make build # Build binary

License

MIT