version: "3.8"

services:
  test:
    image: test
    build:
      context: .
      secrets:
        # invalid target argument
        #
        # According to https://github.com/compose-spec/compose-spec/blob/master/build.md, target is
        # supposed to be the "name of a *file* to be mounted in /run/secrets/". Not a path.
        - source: build_secret
          target: /build_secret

secrets:
  build_secret:
    file: ./my_secret