Pull (fetch & merge) with libgit2

Question

I've been using objecitive-git and libgit2 to try to implement pull functionality. As git pull is just a 'porcelain' command and is made up of a git fetch followed by a git merge origin/master then that would be how I implemented it.

The fetch is performed using the method in objective-git from the fetch branch on github.

[remote fetchWithCredentialProvider:nil error:&error progress:nil];

The code below is what is done after the fetch (which I know succeeds):

// Get the local branch
GTBranch *localBranch = [repo localBranchesWithError:nil][0];
// Get the remote branch
GTBranch *remoteBranch = [repo remoteBranchesWithError:nil][0];

// Get the local & remote commit
GTCommit *localCommit = [localBranch targetCommitAndReturnError:nil];
GTCommit *remoteCommit = [remoteBranch targetCommitAndReturnError:nil];

// Get the trees of both
GTTree *localTree = localCommit.tree;
GTTree *remoteTree = remoteCommit.tree;

// Get OIDs of both commits too
GTOID *localOID = localCommit.OID;
GTOID *remoteOID = remoteCommit.OID;

// Find a merge base to act as the ancestor between these two commits
GTCommit *ancestor = [repo mergeBaseBetweenFirstOID:localOID secondOID:remoteOID error:&error];
if (error) {
    NSLog(@"Error finding merge base: %@", error);
}
// Get the ancestors tree
GTTree *ancestorTree = ancestor.tree;

// Merge into the local tree
GTIndex *mergedIndex = [localTree merge:remoteTree ancestor:ancestorTree error:&error];
if (error) {
    NSLog(@"Error mergeing: %@", error);
}

// Write the merge to disk and store the new tree
GTTree *newTree = [mergedIndex writeTreeToRepository:repo error:&error];
if (error) {
    NSLog(@"Error writing merge index to disk: %@", error);
}

After the mergedIndex which starts out in memory has been written as a tree to disk (writeTreeToRepository uses git_index_write_tree_to) there is no change in the git repos status. I'm assuming I'm missing a last step to make the new tree HEAD or merge it with HEAD or something similar but I'm not sure exactly what.

Any help would be much obliged.

Answer 1

Once you have the tree you want to use for the merge commit, you need to create the merge commit, which you can create with createCommitWithTree in GTRepository the same way as you'd create any other, but with both ancestors as parents. That function also allows you to ask the library to update a particular branch if you expect the repository to be in a quiet state.