Re: Git range merge (cherry-pick a range)

bshOriginal venit, vidit, dixit 16.07.2009 10:11:

Playing around with GIT, we encountered the following strange situation for
which we would
like to have an answer:

Scenario
========

We want to merge the range B to D from branch B1 to master

Master:       o-
                  \
Branch B1:      A-B-C-D-E

Did you use a monospaced font when composing this e-mail? All graphs
come out disconnect/distorted when reading your e-mail with a monospaced
font.

I assume that above, a is the first additional commit of B1 which
branches off o.

Commit B:
---------
FluidSolver::FluidSolver(int argc, char* argv[]) {
    init(argc, argv);
    // test edit 1: a + b
}

Commit C:
--------
FluidSolver::FluidSolver(int argc, char* argv[]) {
    init(argc, argv);
    // test edit 1: a + b
    // test edit 2: a - b
}

Commit D:
--------
FluidSolver::FluidSolver(int argc, char* argv[]) {
    init(argc, argv);
    // test edit 1: a + b
    // test edit 2: a - b
    // test edit 3: a * b
}

Commit E:
--------
FluidSolver::FluidSolver(int argc, char* argv[]) {
    init(argc, argv);
    // test edit 1: a + b
    // test edit 2: a - b
    // test edit 3: a * b
    // test edit 4: a / b
}


Range merge (the GIT way):
=========================

1) Switch to Branch B1

2) Create a temporary branch which does not contain anything beyond commit D

   $ git checkout -b volatileBranch D

    Master:                 o-
                                \
    Branch B1:                A-B-C-D-E
                                                \
    Branch volatileBranch:              (A)-(B)-(C)-(D)

3) Rebase volatile branch to master from commit (B) to master's HEAD
   git rebase --onto master (A) 


    Branch volatileBranch:   (B)-(C)-(D)
                                     /
    Master:                      o-
                                     \
    Branch B1:                   A-B-C-D-E
                                       

Rebasing output:
----------------

First, rewinding head to replay your work on top of it...
Applying: test edit 2: a - b
error: patch failed: fluidsolver.cpp:28
error: fluidsolver.cpp: patch does not apply
Using index info to reconstruct a base tree...
Falling back to patching base and 3-way merge...
Auto-merging fluidsolver.cpp
CONFLICT (content): Merge conflict in fluidsolver.cpp
Failed to merge in the changes.
Patch failed at 0001 test edit 2: a - b


When you have resolved this problem run "git rebase --continue".
If you would prefer to skip this patch, instead run "git rebase --skip".
To restore the original branch and stop rebasing run "git rebase --abort".


Conflicts:
----------
FluidSolver::FluidSolver(int argc, char* argv[]) {
    init(argc, argv);
<<<<<<< HEAD:fluidsolver.cpp
=======
    // test edit 1: a + b
    // test edit 2: a - b

quoted

quoted

quoted

quoted

quoted

quoted

quoted

test edit 2: a - b:fluidsolver.cpp

}


After manually resolving the conflict and continuing the rebasing 
with git rebase --continue, we are finally finished.

Since we only had updates in branch 1, it is astonishing that we get a
conflict at all.
Same situation works like a charme in subversion.

Ahem, how could /anything/ work like a charm in subversion? (I've been
using it myself.)

Seriously, if, in subversion, you merge -rA:D onto master then
subversion only computes the diff between A and D and applies it to
master. You an do this in git as well, of course, but that's not a merge
and does not preserve individual commit messages.

We would be happy to get an explanation for this merge bahaviour, since 
many edits in large projects could as a matter of principle result a lot of
merge conflicts
which all have to be treated manually.

We believe that GIT's interface for range merges needs to get more user
friendly.
Since steps 1) - 3) use already developed components of GIT, there should be
a layer above 'em
which performs a range merge by internally calling 1) - 3).

Example: git cherry-pick $from_branch@startCommitHash
$to_branch@endCommitHash 

If I read you graphs correctly you could just as well fast-forward
master to D (using reset or merge) and then "rebase -i" in order to
remove A.

Alternatively, you can use "git format-patch --stdout revrange | git am".

Michael