The ability to specify an image variant in `args` seems to be removed

[GavinRay97]

Relates to: Both

I noticed something strange today after generating Devcontainer config for a project. The ability to specify the container image tag variant seems to be gone.

Previously when generating a C++ configuration, what I would get is this:

// For format details, see https://aka.ms/devcontainer.json. For config options, see the README at:
// https://github.com/microsoft/vscode-dev-containers/tree/v0.245.2/containers/cpp
{
	"name": "C++",
	"build": {
		"dockerfile": "Dockerfile",
		// Update 'VARIANT' to pick an Debian / Ubuntu OS version: debian-11, debian-10, ubuntu-22.04, ubuntu-20.04, ubuntu-18.04
		// Use Debian 11, Ubuntu 18.04 or Ubuntu 22.04 on local arm64/Apple Silicon
		"args": { "VARIANT": "ubuntu-22.04" }
	},
	"runArgs": ["--cap-add=SYS_PTRACE", "--security-opt", "seccomp=unconfined"],

	// Configure tool-specific properties.
	"customizations": {
		// Configure properties specific to VS Code.
		"vscode": {
			// Add the IDs of extensions you want installed when the container is created.
			"extensions": [
				"ms-vscode.cpptools",
				"ms-vscode.cmake-tools"
			]
		}
	},

	// Use 'forwardPorts' to make a list of ports inside the container available locally.
	// "forwardPorts": [],

	// Use 'postCreateCommand' to run commands after the container is created.
	// "postCreateCommand": "",

	// Comment out to connect as root instead. More info: https://aka.ms/vscode-remote/containers/non-root.
	//
	// NOTE: Commented to make "postCreateCommand" work, if not run as root it fails
	// "remoteUser": "vscode",
	"features": {
		"git": "latest",
		"python": "latest"
	}
}

# See here for image contents: https://github.com/microsoft/vscode-dev-containers/tree/v0.245.2/containers/cpp/.devcontainer/base.Dockerfile
# [Choice] Debian / Ubuntu version (use Debian 11, Ubuntu 18.04/22.04 on local arm64/Apple Silicon): debian-11, debian-10, ubuntu-22.04, ubuntu-20.04, ubuntu-18.04
ARG VARIANT="bullseye"
FROM mcr.microsoft.com/vscode/devcontainers/cpp:0-${VARIANT}

---

However, today what I got was this, which is much less featureful and explanatory IMO:

{
	"name": "C++",
	"build": {
		"dockerfile": "Dockerfile"
	},

	// Use 'forwardPorts' to make a list of ports inside the container available locally.
	// "forwardPorts": [],

	// Use 'postCreateCommand' to run commands after the container is created.
	// "postCreateCommand": "gcc -v",

	// Comment out to connect as root instead. More info: https://aka.ms/vscode-remote/containers/non-root.
	"remoteUser": "vscode",
	"features": {
		"ghcr.io/devcontainers/features/git:1": {},
		"ghcr.io/devcontainers/features/python:1": {}
	}
}

FROM mcr.microsoft.com/devcontainers/cpp:0-ubuntu-22.04

---

Why was the ability to specify the image variant as an ARG of the build removed from the Devcontainer JSON, out of curiosity?

[jkeech]

@GavinRay97 do you mind re-posting this on https://github.com/devcontainers/templates/issues, which is where the templates have moved to? This sounds like feedback on the cpp template: https://github.com/devcontainers/templates/tree/main/src/cpp