Go-Mono is a toolkit for Golang monorepos. The aim is to provide a simple CLI tool which can tell you if a given Go package needs to be rebuilt, based on a dependency tree.

Why build 100 services when only 3 of them have actually changed?

The aim for v1 is to be able to base these decisions entirely on packages within a single repo. This is useful in scenarios where you have a monorepo consisting of a bunch of shared libraries, and applications which are built on top of them. The decision to rebuilt is based on a dependency analysis using Go’s build package to analyse imports, and follow them recursively. Go’s go.mod doesn’t help us here, as these imports are all “local” to the repo.

This functionality will be extended in v2, which will tell you if a package needs to be rebuilt based on relevant dependencies within go.mod. For example, just because go.mod has changed doesn’t mean that you have to rebuild everything in your repo – only things that actually use the changed dependencies. This will work for external dependencies.


A couple of examples.

Example 1

  • Root of repo is the current working directory
  • Package to check is the root of the repo (“.”)
  • Diff against the default branch (“main”)
  • This command returns a non-zero code (1), letting you know that this package needs to be rebuilt
  • It lists the single dependency that has changed

# go-mono
WARN Import has changed                            package=github.com/chrusty/go-mono/internal/git/shell

Example 2

  • Repo in some other directory
  • Package to check is in a subdirectory
  • Diff against a branch called “master”
  • This command returns a non-zero code (1), letting you know that this package needs to be rebuilt
  • It lists the two dependencies which have changed

# go-mono -diff=master -repo=./go/src/github.com/chrusty/protoc-gen-jsonschema -package=cmd/protoc-gen-jsonschema
WARN Import has changed                            package=github.com/chrusty/protoc-gen-jsonschema/internal/converter
WARN Import has changed                            package=github.com/chrusty/protoc-gen-jsonschema/internal/protos

Example 3

  • Nothing has changed

# go-mono
INFO No changes detected


go-mono --help
Usage of go-mono:
    	Run in debug mode?
  -diff string
    	Name of the branch / tag / commit to compare to (default "main")
  -package string
    	Path to the package to analyse (relative to the repo) (default ".")
  -repo string
    	Path to the root of the GIT repo (default ".")
    	Run in trace mode?

How it works

  • Gets a list of files that have changed
    • From the main branch
    • From the previous commit
    • From a named branch / commit / tag
  • For a given list of files / directories (these are the buildable binaries provided by CLI)
    • Analyse their dependency trees
    • Figure out if any of the dependencies are affected by the files in the list of changes
    • Returns a list of “main” packages that need to be built


go install github.com/chrusty/[email protected]


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