lfs: don't add extension to hgrc after clone or share (BC) Now that repository loading in core supports automatically loading the lfs extension when the "lfs" requirement is present, we no longer need to update the .hg/hgrc of newly-created repos to load the lfs extension! I'm marking this as BC because it is a change in behavior. But users should not notice unless they create an LFS repo with new Mercurial and then attempt to use it with an old versions that doesn't support automatic extension loading. Differential Revision: https://phab.mercurial-scm.org/D4712

localrepo: automatically load lfs extension when required (BC) If an unrecognized requirement is present (possibly due to an unloaded extension), the user will get an error message telling them to go to https://mercurial-scm.org/wiki/MissingRequirement for more info. And some requirements clearly map to known extensions shipped by Mercurial. This commit teaches repository loading to automatically map requirements to extensions. We implement support for loading the lfs extension when the "lfs" requirement is present. This behavior feels more user-friendly to me and I'm having trouble coming up with a compelling reason to not do it. The strongest argument I have against is that - strictly speaking - requirements are general repository features and there could be N providers of that feature. e.g. in the case of LFS, there could be another extension implementing LFS support. And the user would want to use this non-official extension rather than the built-in one. The way this patch implements things, the non-official extension could be missing and Mercurial would load the official lfs extension, leading to unexpected behavior. But this feels like a highly marginal use case to me and doesn't outweigh the user benefit of "it just works." If someone really wanted to e.g. use a custom LFS extension, they could prevent the built-in one from being loaded by either defining "extensions.lfs=/path/to/custom/extension" or "extensions.lfs=!", as the automatic extension loading only occurs if there is no config entry for that extension. Differential Revision: https://phab.mercurial-scm.org/D4711

lfs: add repository feature denoting the use of LFS Whether LFS is enabled seems like a useful feature to expose. This will also facilitate some future work around LFS feature compatibility. Differential Revision: https://phab.mercurial-scm.org/D4710