urbit/pkg/arvo/gen/hood/merge/help.txt

Usage:

    |merge %destination-desk ~source-ship %source-desk
    |merge %destination-desk ~source-ship %source-desk, =gem %strategy
    |merge %destination-desk ~source-ship %source-desk, =cas ud+5

We support various merge strategies.  A "commit" is a snapshot of
the files with a list of parents plus a date.   Most commits have
one parent; a "merge" commit is a commit with two parents.  The
%base desk starts with an initial commit with no parents; commits
with several parents ("octopus merges") are possible but we don't
generate them right now.
                                                                      
Unless otherwise specified, all of the following create a new commit
with the source and destination commits as parents.
                                                                      
Several strategies need a "merge-base".  They find it by identifying
the most recent common ancestor of the two desks.  If none, fail
with %merge-no-merge-base; if there are two or more, pick one.
                                                                      
%init: the only way to create a desk.  Not a true merge, since it
simply assigns the source commit to the destination.
                                                                      
%fine: if source or destination are in the ancestry of each other,
use the newer one; else abort.  If the destination is ahead of the
source, succeed but do nothing.  If the source is ahead of the
destination, assign the next revision number to the source commit.
Some call this "fast-forward".
                                                                      
%meet: combine changes, failing if both sides changed the same file.
Specifically, take diff(merge-base,source) and
diff(merge-base,destination) and combine them as long as those diffs
touch different files.
                                                                      
%mate: combine changes, failing if both sides changed the same part
of a file.  Identical to %meet, except that some marks, like %hoon,
allow intelligent merge of changes to different parts of a file.
                                                                      
%meld: combine changes; if both sides changed the same part of a
file, use the version of the file in the merge-base.
                                                                      
%only-this: create a merge commit with exactly the contents of the
destination desk.
                                                                      
%only-that: create a merge commit with exactly the contents of the
source commit.
                                                                      
%take-this: create a merge commit with exactly the contents of the
destination desk except take any files from the source commit which
are not in the destination desk.
                                                                      
%take-that: create a merge commit with exactly the contents of the
source commit except preserve any files from the destination desk
which are not in the source commit.
                                                                      
%meet-this: merge as in %meet, except if both sides changed the same
file, use the version in the destination desk.
                                                                      
%meet-that: merge as in %meet, except if both sides changed the same
file, use the version in the source commit.
                                                                      
# Examples and notes:
                                                                      
The most common merge strategy is %mate, which is a normal 3-way
merge which aborts on conflict.
                                                                      
%take-that is useful to "force" an OTA.  After running %take-that,
you're guaranteed to have exactly the files in the source commit plus
any files you separately added.
                                                                      
We speak of merging into a destination *desk* from a source *commit*
because while you can only merge on top of a desk, you can merge from
historical commits.  For example,
                                                                      
    |merge %old our %base, =cas ud+5, =gem %init
                                                                      
will create a new desk called %old with the 5th commit in %base.
You can revert the contents of a desk to what they were yesterday
with
                                                                      
    |merge %base our %base, =cas da+(sub now ~d1), =gem %only-that
                                                                      
Note this is a normal %only-that merge, which means you're creating a
*new* commit with the old *contents*.
                                                                      
%meld is rarely used on its own, however if you specify %auto or
omit the merge strategy, %kiln will run a %meld merge into a scratch
desk and then annotate the conflicts there.
                                                                      
If you resolve merge conflicts manually, for example by mounting the
desks, copying the files in unix and then running |commit, you
should usually run an %only-this merge.  This will not change the
newly-fixed contents of your desk, but it will record that the merge
happened so that those conflicts don't reappear in later merges.
                                                                      
If you get a %merge-no-merge-base error, this means you're trying to
merge two desks which have no common ancestors.  You need to give
them a common ancestor by choosing a merge strategy which doesn't
need a merge-base, like %only-this, %only-that, %take-this, or
%take-that.
                                                                      
%take-this could be useful to install 3rd party software, but you
couldn't get subsequent updates this way, since the files would
already exist in the destination desk.  Something like "take only
the files which aren't in my OTA source or any other 3rd party app"
would be basically correct.  This would require a parameter listing
the desks to not conflict with.
                                                                      
%meet-this and %meet-that imply the existence of %mate-this and
%mate-that, but those don't exist yet.