pip sdist command

[pfmoore]

pip install -d . XXX can be used to get a sdist for a project off pypi. But it does not work as a general "make a sdist" command - if XXX is a local source directory, it copies the source to the directory specified in -d

Having a dedicated "sdist" command which takes a requirement and builds/downloads a sdist for it (in the same way that pip wheel builds wheels) would be a useful addition.

[qwcode]

sidenote: we should probably make -d give a command failure, except when using with archive urls.

[dstufft]

Closing this, we're probably going to want a command like this when we get abstract build systems, but I don't know that it should live in pip and I don't think we're going to forget about it without an issue to keep track of it.