Const Linter

A Go linter that enforces immutability of struct fields and function parameters marked with special comments.

• Detects assignments to struct fields marked with // +const markers
• Detects modifications to function parameters marked as constant
• Allows field initialization in constructor methods/functions
• Works as a standalone command or as a golangci-lint plugin

Overview

"constlint" is a static analysis tool that helps you enforce immutability in your Go code by detecting unauthorized modifications to:

1. Struct fields marked with // +const comments
2. Function parameters marked with // +const:[param1,param2,...] directive

This linter helps prevent accidental modifications to values that should remain constant after initialization, improving code safety and predictability.

Installation

As a cli

go install github.com/bunniesandbeatings/constlint/cmd/constlint@latest

With golangci-lint (Module Plugin)

To use constlint with golangci-lint as a module plugin, follow these steps:

The Automatic Way (Recommended)

1. Create a .custom-gcl.yml file in your project with the following content:

   version: v1.64.6  # Use your preferred golangci-lint version
   plugins:
     - module: 'github.com/bunniesandbeatings/constlint'
       import: 'github.com/bunniesandbeatings/constlint/plugin'
       version: v1.0.0  # Use the appropriate version

2. Configure golangci-lint to use the plugin by adding the following to your .golangci.yml file:

   linters-settings:
     custom:
       constlint:
         type: "module"
         description: Checks for writes to struct fields marked with // +const
   
   linters:
     enable:
       - constlint

3. Build your custom golangci-lint binary:

   golangci-lint custom

4. Run your custom golangci-lint:

   ./custom-gcl run

The Manual Way

1. Clone the golangci-lint repository:

   git clone https://github.com/golangci/golangci-lint.git
   cd golangci-lint

2. Add a blank import for the constlint plugin in cmd/golangci-lint/plugins.go:

   import (
       // Add other imports...
       
       // Add constlint plugin
       _ "github.com/bunniesandbeatings/constlint/plugin"
   )

3. Run go mod tidy and build golangci-lint:

   go mod tidy
   make build

4. Configure your .golangci.yml file as shown in the automatic method above.

5. Run your custom golangci-lint binary.

Examples

Look in the testdata folder for examples.