Import Boundary Checker for Golang

About

Import Boundary Checker is a tool to automatically check if import boundaries are violated or not. Examples of where this tool is useful:

• Hexagonal/clean architecture where domain logic cannot import infrastructure code
• Mono-repositories with multiple microservices where you don't allow services to import code from other microservices
• Layered architecture where layers cannot import certain other layers

Why is this tool useful, and why consider using it over alternative tools?

• Import boundaries are checked automatically (meaning you don't have to spend time in code review on manually checking)
• It is extremely fast (sub-second speeds with medium sized projects)
• Configuration is easy (within a few minutes you can define forbidden imports for your projects and have everything set up)
• The tool is independent (you don't need to change any production or testing code for the tool to work)
• Usage of the tool requires zero dependencies (so no outside dependencies are needed for running the tool, only the source code of your project)

Installation

You will need Go 1.14+.

go install github.com/BytecodeAgency/import-boundary-checker

Note: due to being in the alpha phase, the tool has only been tested on MacOS and Linux. Windows support is not guaranteed but will be added before the 1.0.0 release.

Usage

After setting your configuration and, you can invoke the tool by simply calling:

import-boundary-checker

Note that only production code (not the test modules) is tested.

You can use the following CLI options (they are all optional):

• -config [filepath]: set the configuration path (defaults to .importrules in the current directory)
• -verbose: set verbose output of main (does not enable debugging mode)

Configuration DSL

Note: the semicolons are required!

The tool is configured using a domain specific language. Follow the steps below to create your configuration:

0. Create a new configuration file .importrules in the root directory of the project you want to check

1. Set the correct language for your project (currently only Go is supported, Typescript/Javascript will be added next)

LANG "Go";

2. Set the IMPORTBASE variable (this is the same as the module value in go.mod)

IMPORTBASE "github.com/BytecodeAgency/example";

3. Define the import boundaries, using IMPORTRULE "[IMPORTBASE]{file you are defining forbidden imports for} CANNOTIMPORT "[IMPORTBASE]/{some module in project}" "[IMPORTBASE]/{another module in project}";. Leaving out the [IMPORTBASE] allows you to define forbidden imports from the standard library or outside dependencies. Whitespace is ignored. Note that when defining an import, importing from subdirectories within the given module will also cause errors (given /domain, will also block /domain/user and /domain/user/models, etc.)

IMPORTRULE "[IMPORTBASE]/typings/entities"
CANNOTIMPORT "[IMPORTBASE]" "fmt" "github.com/go-playground/validator/v10";

IMPORTRULE "[IMPORTBASE]/domain"
CANNOTIMPORT
    "[IMPORTBASE]/infrastructure"
    "[IMPORTBASE]/data";

4. When defining import boundaries, you can optionally add allowed imports, using ALLLOW "{allowed module}" "allowed module" (make sure you do this before the semicolon). This is useful f.e. when working with hexagonal architecture.

IMPORTRULE "[IMPORTBASE]/domain"
CANNOTIMPORT
    "[IMPORTBASE]/infrastructure"
    "[IMPORTBASE]/data"
ALLOW "[IMPORTBASE]/data/interactors";

This will give the following configuration file:

LANG "Go";
IMPORTBASE "github.com/BytecodeAgency/example"

IMPORTRULE "[IMPORTBASE]/typings/entities"
CANNOTIMPORT "[IMPORTBASE]" "fmt" "github.com/go-playground/validator/v10";

IMPORTRULE "[IMPORTBASE]/domain"
CANNOTIMPORT
    "[IMPORTBASE]/infrastructure"
    "[IMPORTBASE]/data"
ALLOW "[IMPORTBASE]/data/interactors";

5. When working with hexagonal architecture it might be intereseting to block all imports at the root of the project and allow the specific imports in the more specific sub folders.

LANG "Go";
IMPORTBASE "github.com/BytecodeAgency/example"

IMPORTRULE "[IMPORTBASE]"
CANNOTIMPORT "[IMPORTBASE]";

IMPORTRULE "[IMPORTBASE]/entities"
CANNOTIMPORT "fmt"

IMPORTRULE "[IMPORTBASE]/interactors"
ALLOW "[IMPORTBASE]/entities";

IMPORTRULE "[IMPORTBASE]/data"
ALLOW 
    "[IMPORTBASE]/entities"
    "[IMPORTBASE]/interactors";

You can read the full DSL specification in the docs/dsl.md file.

Full examples

In the examples directory of this repository, you can find some examples of the tool configured. In each directory, you will find a .importrules file with the import boundaries defined.

An example for running this in CI through Docker can be found in the Dockerfile in the root of this repository.

License and contribution

The project is licensed under the Lesser GNU Public Licence version 3 (LGPLv3). Contributions (issues and pull requests) are welcome.

Development documentation can be found in docs/dev.md.