structfieldsenforcer

A Go static analysis tool that enforces mandatory struct field initialization using struct tags.

Installation

go install github.com/flaticols/structfieldsenforcer@latest

Usage

Mark struct fields as mandatory using tags:

type Config struct {
    DatabaseURL string `mandatory:""`
    APIKey      string `mandatory:""`
    Port        int    `mandatory:""`
    Debug       bool   // Optional field
}

The tool detects violations like:

config := Config{
    DatabaseURL: "postgres://localhost/mydb",
    // Missing APIKey and Port
}

Quick Start

# Check for violations
structfieldsenforcer ./...

# Fix violations by adding TODO comments
structfieldsenforcer -fix ./...

# Generate missing constructors
structfieldsenforcer -fix -constructors=gen ./...

# Update existing constructors
structfieldsenforcer -fix -constructors=update ./...

Fix Examples

Before fixing:

config := Config{
    DatabaseURL: "postgres://localhost/mydb",
    Debug:       true,
}

After structfieldsenforcer -fix:

config := Config{
    DatabaseURL: "postgres://localhost/mydb",
    Debug:       true,
    APIKey:      // TODO: provide value for APIKey,
    Port:        // TODO: provide value for Port,
}

After structfieldsenforcer -fix -constructors=gen:

Important

The analyzer intentionally creates compilation errors with TODO comments to ensure you don't miss mandatory fields that need values.

config := Config{
    DatabaseURL: "postgres://localhost/mydb",
    Debug:       true,
    APIKey:      // TODO: provide value for APIKey,
    Port:        // TODO: provide value for Port,
}

func NewConfig(apikey string, databaseURL string, port int) *Config {
    return &Config{APIKey: apikey, DatabaseURL: databaseURL, Port: port}
}

Constructor Update Example:

If you have an existing constructor missing mandatory fields:

func NewConfig(databaseURL string) *Config {
    return &Config{DatabaseURL: databaseURL}
}

After structfieldsenforcer -fix -constructors=update:

func NewConfig(apikey string, databaseURL string, port int) *Config {
    return &Config{APIKey: apikey, DatabaseURL: databaseURL, Port: port}
}

Commands

Basic Usage

• structfieldsenforcer ./... - Check for violations in all packages
• structfieldsenforcer -fix ./... - Fix violations by adding TODO comments
• structfieldsenforcer main.go - Check specific file

Constructor Operations

• structfieldsenforcer -constructors=gen ./... - Check what constructors can be generated
• structfieldsenforcer -constructors=update ./... - Check what constructors can be updated
• structfieldsenforcer -constructors=gen,update ./... - Check both operations

Fixing with Constructors

• structfieldsenforcer -fix -constructors=gen ./... - Fix violations AND generate constructors
• structfieldsenforcer -fix -constructors=update ./... - Fix violations AND update existing constructors
• structfieldsenforcer -fix -constructors=gen,update ./... - Fix violations, generate AND update constructors

Advanced Usage

• structfieldsenforcer -tag=required ./... - Use custom tag name
• structfieldsenforcer -constructor-patterns="New*,Build*,Make*" ./... - Custom constructor patterns
• structfieldsenforcer -fix -tag=required -constructors=gen -constructor-patterns="Build*" ./pkg/... - Complex combination

Options

Core Flags

• -tag string - Custom tag name for mandatory fields (default: "mandatory")
  Example: -tag=required to use required:"" instead of mandatory:""

• -fix - Apply fixes to files. Without this flag, only reports violations without modifying files
  Example: -fix enables file modifications

• -help - Show help message and exit
  Example: -help displays usage information

Constructor Operations

• -constructors string - Constructor operations to perform:

  • gen - Generate missing constructors for structs with violations
  • update - Update existing constructors to include all mandatory fields
  • gen,update - Both generate and update constructors

  Important: Constructor operations only modify files when combined with -fix. Without -fix, they only report what would be done.

• -constructor-patterns string - Comma-separated patterns to identify constructor functions (default: "New*,Create*")

  • Supports glob patterns with * wildcard
  • Examples: "New*", "Create*", "Build*", "New*,Create*,Build*"
  • Functions matching these patterns will be treated as constructors

Command Line Reference

Package Patterns

The tool accepts Go package patterns as arguments:

• ./... - Recursively analyze all packages in current directory (default)
• ./pkg/... - Recursively analyze packages in pkg directory
• file.go - Analyze specific file
• pkg1 pkg2 - Analyze multiple specific packages
• . - Analyze current directory only (non-recursive)

Exit Codes

• 0 - Success, no violations found
• 1 - Violations found (or would be found in check-only mode)
• 2 - Syntax or parsing errors in Go files
• 3 - File system errors (permissions, file not found, etc.)

Flag Combinations

Flags	Behavior
(none)	Check for violations, exit with code 1 if found
-fix	Fix violations by adding TODO comments
-constructors=gen	Check what constructors can be generated
-constructors=update	Check what constructors can be updated
-fix -constructors=gen	Fix violations AND generate missing constructors
-fix -constructors=update	Fix violations AND update existing constructors
-fix -constructors=gen,update	Fix violations, generate AND update constructors

Key Rule: Constructor operations (-constructors) only modify files when -fix is also specified.

License

MIT