largefiles: explicitly set the source and sink types to 'hg' for lfconvert I stumbled into this prior to adding the type indicator on the source and sink, but there's no reason to try to infer the types for this conversion.

lfs: add a repo requirement for this extension when converting to lfs This covers both the vanilla repo -> lfs repo and largefiles -> lfs conversions. The largefiles extension adds the requirement directly, because it has a dedicated command to convert. Using the convert extension is better, because it supports more features. I'd like ideas about how to ensure that converting away from lfs works on all files. (See comments in test-lfs.t)

convert: allow the sink object to be wrapped when the extension isn't loaded The next patch will wrap the conversion code, in order to write out a requirement for 'lfs' when appropriate. Wrapping convcmd.convertsink() in an afterloaded callback works fine when the convert extension is enabled by the user. The problem here is that lfconvert uses the convert extension, whether or not it was formally enabled by the user. My first attempt was to have lfs install an afterloaded callback that would wrap the convert sink if convert was loaded, or wrap lfconvert if it wasn't. Then the lfconvert override could install an afterloaded callback to try wrapping the convert sink again, before calling the original lfconvert. But that breaks down if largefiles can't load the convert extension on the fly. [1] Further, some tests were failing with an error indicating that the size of the afterloaded list changed while iterating it. Yuya mentioned that maybe some bits of convert could be moved into core, but I'm not sure where to draw that line. The convertsink() method depends on the list of sinks, which in turn depends on the sink classes. [1] https://www.mercurial-scm.org/pipermail/mercurial-devel/2017-November/108038.html

convert: save an indicator of the repo type for sources and sinks This seems like basic info to have, and will be used shortly when deciding whether or not to wrap the class for lfs conversions. The other option is to just add a function to each class. But this seems better in that the strings aren't duplicated, and the constructor for most of these will run even if the VCS isn't installed, so it's easier to catch errors.