documentation: add some internals documentation about bid merge
This is an important algorithm that was only documented on the wiki so far.
Some update to the algorithm (and associated doc) is to expected in the future
since the bid merge algorithm is bug-ridden when it comes to file deletion comes
to play.
Differential Revision: https://phab.mercurial-scm.org/D8711
$ hg init
$ mkdir d1 d1/d11 d2
$ echo d1/a > d1/a
$ echo d1/ba > d1/ba
$ echo d1/a1 > d1/d11/a1
$ echo d1/b > d1/b
$ echo d2/b > d2/b
$ hg add d1/a d1/b d1/ba d1/d11/a1 d2/b
$ hg commit -m "intial"
Test single file
# One recorded copy, one copy to record after commit
$ hg cp d1/b d1/c
$ cp d1/b d1/d
$ hg add d1/d
$ hg ci -m 'copy d1/b to d1/c and d1/d'
$ hg st -C --change .
A d1/c
d1/b
A d1/d
# Errors out without --after for now
$ hg cp --at-rev . d1/b d1/d
abort: --at-rev requires --after
[255]
# Errors out with non-existent source
$ hg cp -A --at-rev . d1/non-existent d1/d
d1/non-existent: no such file in rev 55d1fd85ef0a
abort: no files to copy
[255]
# Errors out with non-existent destination
$ hg cp -A --at-rev . d1/b d1/non-existent
abort: d1/non-existent: copy destination does not exist in 8a9d70fa20c9
[255]
# Successful invocation
$ hg cp -A --at-rev . d1/b d1/d
saved backup bundle to $TESTTMP/.hg/strip-backup/8a9d70fa20c9-973ae357-copy.hg
# New copy is recorded, and previously recorded copy is also still there
$ hg st -C --change .
A d1/c
d1/b
A d1/d
d1/b
Test moved file (not copied)
$ hg co 0
0 files updated, 0 files merged, 2 files removed, 0 files unresolved
$ mv d1/b d1/d
$ hg rm -A d1/b
$ hg add d1/d
$ hg ci -m 'move d1/b to d1/d'
created new head
$ hg cp -A --at-rev . d1/b d1/d
saved backup bundle to $TESTTMP/.hg/strip-backup/519850c3ea27-153c8fbb-copy.hg
$ hg st -C --change .
A d1/d
d1/b
R d1/b
Test using directory as destination
$ hg co 0
1 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ cp -R d1 d3
$ hg add d3
adding d3/a
adding d3/b
adding d3/ba
adding d3/d11/a1
$ hg ci -m 'copy d1/ to d3/'
created new head
$ hg cp -A --at-rev . d1 d3
abort: d3: --at-rev does not support a directory as destination
[255]