Test: target and build args properties in devcontainer.json

[chrmarti]

Refs: #46

• anyOS @aeschli
• anyOS @sbatten

Complexity: 4

---

On setting up DevContainers for testing: https://github.com/microsoft/vscode-remote-containers/blob/master/CONTRIBUTING.md#testing-remote-containers

Test the new target and build args properties and the alternative placing of dockerfile and context (check that dockerFile and context can still be used as top-level properties):

{
    "build": {
        "dockerfile": "...",
        "context": "...",
        "target": "...",
        "args": {
            "FOO": "BAR"
        }
    }
}

Note that the top-level dockerFile property has a capital F (for compatibility) and the nested property is all lowercase dockerfile (for consistency with Dockerfile).

Docker documentation for target: https://docs.docker.com/engine/reference/commandline/build/#specifying-target-build-stage---target

Docker documentation for build args: https://docs.docker.com/engine/reference/builder/#arg

Example Dockerfile for testing:

FROM node:12 AS base

RUN touch /foobar.base

FROM base AS dev

RUN touch /foobar.dev

ARG FOO=BAR
RUN echo $FOO >/foo.txt

FROM base AS prod

RUN touch /foobar.prod

[chrmarti]

Note that the casing for dockerfile inside build changed to all lowercase in 0.104.0 of the extension (schema update in 2/26 Insiders). The top-level property is still dockerFile with a capital F for compatibility.