enabling hcp multibuilds

[mogrogan]

HCP Packer multibuilds

This Pr will remove the check that prevents user from using multiple build block in HCL2 configuration.

Example

// multi-build.pkr.hcl

packer {
  required_plugins {
    docker = {
      version = ">= 1.0.0"
      source  = "github.com/hashicorp/docker"
    }
  }
}

hcp_packer_registry {
  bucket_name = "my-bucket"
  description = "some packer test"
}

source "docker" "debian" {
  image  = "debian"
  commit = true
}

source "docker" "alpine" {
  image  = "alpine"
  commit = true
}

build {
  sources = ["source.docker.debian"]
}

build {
  sources = ["source.docker.alpine"]
}

Output:

$ packer build multi-build.pkr.hcl
Tracking build on HCP Packer with fingerprint "01JPB2F0B22PT3G7BSQCQ6RGC3"
docker.debian: output will be in this color.
docker.alpine: output will be in this color.

==> docker.debian: Creating a temporary directory for sharing data...
==> docker.debian: Pulling Docker image: debian
==> docker.alpine: Creating a temporary directory for sharing data...
==> docker.alpine: Pulling Docker image: alpine
    docker.debian: Using default tag: latest
    docker.alpine: Using default tag: latest
    docker.debian: latest: Pulling from library/debian
    docker.alpine: latest: Pulling from library/alpine
    docker.debian: Digest: sha256:35286826a88dc879b4f438b645ba574a55a14187b483d09213a024dc0c0a64ed
    docker.debian: Status: Image is up to date for debian:latest
    docker.debian: docker.io/library/debian:latest
    docker.alpine: Digest: sha256:a8560b36e8b8210634f77d9f7f9efd7ffa463e380b75e2e74aff4511df3ef88c
    docker.alpine: Status: Image is up to date for alpine:latest
    docker.alpine: docker.io/library/alpine:latest
==> docker.debian: Starting docker container...
    docker.debian: Run command: docker run -v /Users/martin.grogan/.config/packer/tmp29564845:/packer-files -d -i -t --entrypoint=/bin/sh -- debian
==> docker.alpine: Starting docker container...
    docker.alpine: Run command: docker run -v /Users/martin.grogan/.config/packer/tmp3773282027:/packer-files -d -i -t --entrypoint=/bin/sh -- alpine
    docker.debian: Container ID: 75b2aaf56a0acc1aadb291c95642ca73a224b225620bd7f8099929e424e39dc1
==> docker.debian: Using docker communicator to connect: 172.17.0.2
    docker.alpine: Container ID: 5d2267087a3c4a43c6be7df47153c731e031b28cc51a6920ec639a04ed4fe5dc
==> docker.alpine: Using docker communicator to connect: 172.17.0.3
==> docker.debian: Committing the container
==> docker.alpine: Committing the container
    docker.alpine: Image ID: sha256:1efbdd66f335465890f8e97e289facc2653e6983638f32891f1c9227008350cc
==> docker.alpine: Killing the container: 5d2267087a3c4a43c6be7df47153c731e031b28cc51a6920ec639a04ed4fe5dc
    docker.debian: Image ID: sha256:0350cdd87d4183a1106bd164ab8feb72da9cc3fcc71919239cf09d57b48ad9c3
==> docker.debian: Killing the container: 75b2aaf56a0acc1aadb291c95642ca73a224b225620bd7f8099929e424e39dc1
Build 'docker.alpine' finished after 1 second 236 milliseconds.
Build 'docker.debian' finished after 1 second 361 milliseconds.

==> Wait completed after 1 second 531 milliseconds

==> Builds finished. The artifacts of successful builds are:
--> docker.alpine: Imported Docker image: sha256:1efbdd66f335465890f8e97e289facc2653e6983638f32891f1c9227008350cc
--> docker.alpine: Published metadata to HCP Packer registry packer/my-bucket/versions/01JPB2F0PY3NYSP3FDNEDQZ9VG
--> docker.debian: Imported Docker image: sha256:0350cdd87d4183a1106bd164ab8feb72da9cc3fcc71919239cf09d57b48ad9c3
--> docker.debian: Published metadata to HCP Packer registry packer/my-bucket/versions/01JPB2F0PY3NYSP3FDNEDQZ9VG

On the HCP Packer portal:

(Note that it's version 4 since I tested some combination before)

[lbajolet-hashicorp]

Left one small nit on a diagnostic message, but besides that, it looks good to me!

[lbajolet-hashicorp]

Some small adjustments on the diagnostics, another small nit on the test code, but besides those, LGTM!

[lbajolet-hashicorp]

You can probably remove this instead of commenting it

[lbajolet-hashicorp]

Suggested change

	"two build has the same name causing a conflict, there must only "+
	"two builds have the same name, causing a conflict, there must only "+

[lbajolet-hashicorp]

I would suggest pointing out at the lack of a build name here instead as the summary

Suggested change

	Summary: "Build name conflicts",
	Summary: "Missing mandatory build name",

[lbajolet-hashicorp]

Suggested change

	Detail: "build name is required when using the same source in two different builds",
	Detail: "A build name is required when using the same source in two or more different builds",

[lbajolet-hashicorp]

Likely not an issue, but if we don't have a build block defined here, what happens? I'm not sure we even reach this code, but I wonder if the check here shouldn't be exactly len(cfg.Builds) == 1 instead of a <=, otherwise we'll crash on the following statement since cfg.Builds[0] will be out-of-bounds