On 3 June 2017 at 03:14, Nathaniel Smith email@example.com wrote:
So far my belief is that packages with expensive build processes are going to ignore you and implement, ship, document, and recommend the direct source-tree->wheel path for developer builds. You can force the make-a-wheel-from-a-directory-without-copying-and-then-install-it command have a name that doesn't start with "pip", but it's still going to exist and be used. Why wouldn't it? It's trivial to implement and it works, and I haven't heard any alternative proposals that have either of those properties. 
I may be misunderstanding you, but it's deeply concerning if you're saying "as a potential backend developer, I'm sitting here listening to the discussion about PEP 517 and I've decided not to raise my concerns but simply to let it be implemented and then ignore it". OTOH, I'm not sure how you plan on ignoring it - are you suggesting that projects like numpy won't support "pip install numpy" except for wheel installs?
One thing that's not clear to me: a crucial use case for sdists is (1) download, (2) unpack, (3) patch the source, possibly adding new files, (4) build and install. (After all, the whole reason we insist on distributing sdists is that open source software should be modifiable by the recipient.) Does flit currently support this, given the reliance on VCS metadata?
That's a reasonable concern, and a reservation I have about flit's sdist support, but as a comment about flit, it probably belongs more on the flit tracker than here.
As a point for PEP 517, I think it's valid though. I'd suggest that the PEP add a few more lines on what constitutes a "source tree", by offering some examples. It seems to me that the two key examples of a "source tree" that the PEP must support are
(The second of these being the one we're talking about here).
 By "won't support" consider that in a PEP 517 world, pip issues stating "pip install <numpy source checkout> takes too long" or similar will be passed to the backend developer with the suggestion that they implement the build_sdist or copy_files hook. Saying numpy won't support PEP 517 means that such requests will be denied.