Option to build with an existing conda

[dagewa]

@biochem-fan reports that building DIALS with an existing conda set up is possible by editing the conda_exe variable in bootstrap.py. Is this something we should enable as an option to bootstrap.py? It may help for integrating DIALS within other systems.

[Anthchirp]

fwiw, I deliberately removed that feature from our bootstrap, as it just makes support harder. In my opinion we should not support that - bootstrap should give you a well defined development installation (specifically: for developing DIALS). All other use cases should install DIALS, ideally from a conda-forge package rather than bootstrap.

[dagewa]

That's reasonable. When we talk about a new installer, are we keeping in mind the situation where the user wants to use their own Python, in order to build DIALS into some larger system? In that case, what requirements would there be of that Python (such as, should it be a conda-aware Python)?