help: add internals.extensions topic
I think it's better to include the API overview in core as we now have the
internals section in our help system.
Retrieved from the wiki, and formatted as reST. Several wiki links are
removed since they are invalid in the help. The sections about example
extension are removed at all as they seemed too verbose.
https://www.mercurial-scm.org/wiki/WritingExtensions
$ . "$TESTDIR/remotefilelog-library.sh"
$ hg init master
$ cd master
$ cat >> .hg/hgrc <<EOF
> [remotefilelog]
> server=True
> serverexpiration=-1
> EOF
$ echo x > x
$ hg commit -qAm x
$ echo y > y
$ hg commit -qAm y
$ echo z > z
$ hg commit -qAm z
$ cd ..
$ hgcloneshallow ssh://user@dummy/master shallow -q
3 files fetched over 1 fetches - (3 misses, 0.00% hit ratio) over *s (glob)
# Compute keepset for 0th and 2nd commit, which implies that we do not process
# the 1st commit, therefore we diff 2nd manifest with the 0th manifest and
# populate the keepkeys from the diff
$ cd shallow
$ cat >> .hg/hgrc <<EOF
> [remotefilelog]
> pullprefetch=0+2
> EOF
$ hg debugkeepset
# Compute keepset for all commits, which implies that we only process deltas of
# manifests of commits 1 and 2 and therefore populate the keepkeys from deltas
$ cat >> .hg/hgrc <<EOF
> [remotefilelog]
> pullprefetch=all()
> EOF
$ hg debugkeepset