localrepo: automatically load lfs extension when required (BC)...
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
