Write a Dagger Function to Build a Go Project

In the previous challenge, you learned how to create a Dagger module with a few dummy Dagger Functions in it. Now you will need to create a more useful module - one that can build a multi-arch Go project.

The sample Go project is located in ~/my-project. Explore it, paying special attention to the Makefile. After that, in the project's root directory, bootstrap a Dagger module. The module should have only one Dagger Function, which performs the same go build command that the Makefile uses. The function should take in the project's root directory and the target architecture, execute the go build command, and return the resulting binary file.

The solution checker will use the following commands to verify the implementation:

# Assuming the PWD is the project's root directory

dagger call build --src . --arch arm64 export --path ./server
dagger call build --src . --arch amd64 export --path ./server

Good luck!

Hint 1 💡

Don't know where to start? Check out this post on writing Dagger Functions.

Hint 2 💡

The function should conform to the following signature:

import (
  "dagger/my-project/internal/dagger"
)

type MyProject struct{}

func (m *MyProject) Build(
  src *dagger.Directory,
  arch string,
) *dagger.File {
  // Your implementation goes here...
}

The above is Go code, but you're free to use any of the supported languages.

Hint 3 💡

Even though Dagger Functions are written in full-blown programming languages, they often look like a bunch of shell commands glued together with Go (or Python, or TypeScript, or whatever). Something still has to execute that go build command.

Hint 4 💡

Tried executing the go build command directly from the build function and it failed? To be able to run the go build command, you need a proper Go development environment, and the function's runtime is definitely not suitable for that.

Dagger uses additional containers to provision required environments for every command execution. Here is what you can do:

func (m *MyProject) Build(
  src *dagger.Directory,
  arch string,
) *dagger.File {
  buildContainer := dag.Container().
    From("golang:1").
      WithDirectory("/src", src).
      WithExec([]string{"go", "build", "..."})
    ...
}