[Distutils] abstract build system approaches redux

[Paul Moore]

On 3 March 2016 at 13:44, Donald Stufft <donald at stufft.io> wrote:
> * If we're using a CLI based thing, we need to create a negotiation phase,
>   which I think is a bad idea because it's kind of complicated and error prone.
>   Looking at TLS or HTTP, there's more than one bug that exists because of
>   this.

Additionally, it seems to me that a negotiation means additional
round-trips to the build system. Which means extra subprocess calls.
On Windows in particular, the cost of a subprocess call is not that
cheap, so this could result in increased build times.

I understand that the actual build steps will likely always involve a
subprocess, for isolation purposes. But avoiding subprocess calls for
"admin" issues like "what version of the protocol do you support?" is
a worthwhile goal.

(Beyond noting the above as a data point, I don't really have a strong
opinion on a CLI vs Python interface, though).

Paul