Patrol

Patrol is a utility to help you understand what packages within a Go module changed between commits. It was created to be used within CI pipelines to only build what needs to be built, but maybe someone else can find a cool use for this :). Patrol currently detects changes in:

• packages within the module itself
• go.mod dependency
• vendored dependencies

To understand all (potential) changes, Patrol traverses the whole dependencies graph which means that if you have a structure that looks like this

external-package@v1.0.0 -> yourModule/foo -> yourModule/bar

and you update external-package to version v1.0.1 Patrol will report yourModule/foo (depending on external-package) and yourModule/bar (depending on yourModule/foo) as changed.

Getting started

Install as binary

Patrol can be installed as any other Go binary, you just need to run

go install github.com/utilitywarehouse/patrol

and you can use it like this patrol -from={commit hash} {path to your repo}

This is an example run against one of our teams monorepo:

$ patrol -from=0a359e246ba3c7c76b0ad0e1d734ae103455b7a9 .

github.com/utilitywarehouse/my-services-mono/services/broadband-services-api/cmd/broadband-services-api
github.com/utilitywarehouse/my-services-mono/pkg/broadband
github.com/utilitywarehouse/my-services-mono/services/energy-services-projector/cmd/energy-services-projector
github.com/utilitywarehouse/my-services-mono/services/energy-services-projector/internal/handler

Patrol does nothing more than reporting what packages (or other packages they depend on) changed in between commits. If for example your goal is to understand what Docker images you should build as part of your CI run, and you know your executables live under services/, you could by filtering your results with ripgrep:

$ patrol -from=0a359e246ba3c7c76b0ad0e1d734ae103455b7a9 . | rg services

github.com/utilitywarehouse/my-services-mono/services/broadband-services-api/cmd/broadband-services-api
github.com/utilitywarehouse/my-services-mono/services/energy-services-projector/cmd/energy-services-projector
github.com/utilitywarehouse/my-services-mono/services/energy-services-projector/internal/handler

Use as a Go library

If you want to integrate Patrol into your scripts, and your scripts are written in Go (maybe using something like mage) you can easily do so:

package main

import (
	"fmt"

	"github.com/utilitywarehouse/patrol/patrol"
)

func main() {
	repo, err := patrol.NewRepo("path/to/your/repo")
	if err != nil {
		panic(err)
	}

	revision := "a0e002f951f56d53d552f9427b3331b11ea66e92"

	changes, err := repo.ChangesFrom(revision)
	if err != nil {
		panic(err)
	}

	for _, c := range changes {
		fmt.Println(c)
	}
}

Contributing

So did Patrol blow up on you or you finally saw an actual stack overflow? Graphs do that sometimes. Sorry if that happened, but if you found you want to improve or fix I'd suggest starting by writing a test.

Tests in this are fairly peculiar, but we need other repositories to test a tool like Patrol. You can take a look at any of the case defined in testdata but here's a checklist that might help:

• add a new folder within patrol/testdata with a name expressing what you're trying to test
• add as many folders as you'd like to patrol/testdata/{your-test}/commits. Each folder represents an actual commit, and they will be applied on top of each other as real commits when tests are run. Each commit following the first one should contain a changes.patrol file that lists the output you expect from Patrol for that test (don't worry, order doesn't matter here). You can check this example.
• add a new test case in patrol/repo_test.go