certain image names in duffle.json produce spurious images in bundle

[glyn]

The following duffle.json:

{
    "name": "imagebug",
    "version": "1",
    "schemaVersion": "v1.0.0-WD",
    "invocationImages": {
        "cnab": {
            "name": "cnab",
            "builder": "docker",
            "configuration": {
                "registry": "imagebug"
            }
        }
    },
    "images": {
        "x.y": {
            "image": "docker.io/cloudfoundry/cnb@sha256:93e2707b756ed9544ecccab6884424e4990e2b3ec08f0435b8249499b51b2354",
            "digest": "sha256:93e2707b756ed9544ecccab6884424e4990e2b3ec08f0435b8249499b51b2354"
        }
    }
}

when input to duffle build, produces an invalid images section of bundle.json:

{
  "description": "",
  "images": {
    "x": {
      "description": "",
      "image": "",
      "imageType": ""
    }
  },
  "invocationImages": [
    {
      "image": "imagebug/imagebug-cnab:32ff5be1120468ffcb5c37226c5348276b9de209",
      "imageType": "docker"
    }
  ],
  "name": "imagebug",
  "schemaVersion": "v1.0.0-WD",
  "version": "1.0.0"
}

This seems superficially like https://github.com/deislabs/duffle/issues/658, which was apparently fixed.

Possible clue

Change x.y to x in duffle.json and the correct bundle is produced:

{
  "description": "",
  "images": {
    "x": {
      "description": "",
      "image": "docker.io/cloudfoundry/cnb@sha256:93e2707b756ed9544ecccab6884424e4990e2b3ec08f0435b8249499b51b2354",
      "imageType": ""
    }
  },
  "invocationImages": [
    {
      "image": "imagebug/imagebug-cnab:32ff5be1120468ffcb5c37226c5348276b9de209",
      "imageType": "docker"
    }
  ],
  "name": "imagebug",
  "schemaVersion": "v1.0.0-WD",
  "version": "1.0.0"
}

Steps to reproduce (at least on macOS)

• Grab duffle from https://github.com/deislabs/duffle/releases/tag/0.2.0-beta.3 and add it to your path
• Download and unzip build.zip
• cd into the unpacked archive and into the build subdirectory
• issue duffle build . -o outbundle.json
• observe the images section of outbundle.json

[glyn]

This appears to be a side-effect, or probably a feature, of https://github.com/spf13/viper (and the underlying https://github.com/mitchellh/mapstructure).

[glyn]

Note that https://github.com/deislabs/duffle/issues/752 changed duffle so that it is intended to take only duffle.json as input (no TOML or YAML thank you), so we are free to switch from viper to standard JSON parsing.

[carolynvs]

I vote for removing viper now that we don't need multiple file formats anymore in duffle. We can just go back to using encoding/json.