Option name for singularity

[BoPeng]

nextflow uses the following configurations for singularity:

process.container = 'file:///path/to/singularity.img'
singularity.enabled = true

where process.container can be file (local file), docker:// (pull from docker hub), and shub (pull from sigularity hub).

We currently have

container = 'image' (equivalent to 'docker://image')
container = 'docker://image'

that assumes the use of docker.

container = 'file://file'
container = 'shub://url'

can assume the use of singularity, but what if we want to use singularity to execute docker container? Should we have

container='image', singularity=True

or

container='docker://image', singularity=True

or

container='image', engine='singularity'

so that we can support other types of engines (e.g. shifter)?

[gaow]

container='image', engine='singularity'

this looks good to me.

[BoPeng]

Thanks, used engine='singularity'.