[Distutils] A possible refactor/streamlining of PEP 517

[Thomas Kluyver]

On Fri, Jul 14, 2017, at 11:18 AM, Nathaniel Smith wrote:
> OTOH this whole 11th hour discussion of forcing every build system to
> have in-tree and out-of-tree build support is solving some other
> problem. 

It is not my intention to force build systems to support either of
these.

- Where build systems only support out-of-tree builds, it should be
trivial to create a temporary directory when build_directory is not
passed.
- Where build systems only support in-tree builds, they should copy the
necessary files to build_directory and run an in-tree build there. This
is more complex, but it appears to be non-negotiable that there is some
way of building without affecting the source directory, so whatever the
interface is, we need some way to do this.