Implementing merge with default options

[victorgp]

This pull request implements the merge operation based on the default options libgit2 defines.

The merge receives an Oid and returns a MergeResult object.

This MergeResult object is quite similar than the git_merge_result libgit2 implements. it has:

->is_fastforward: boolean field that indicates the merge was fastforward
->is_uptodate: boolean field that indicates the merge was already up to date
->fastforward_oid: python Oid object with the new fastforward Oid to be the new head (only if the merge was fastforward, None otherwise)
->status: dict with the repository status after the merge (if the merge was not fastforward, either there were conflicts or not, an empty dict otherwise)

Some notes:
-The merge, as it name says, only does the merge, it does not perform any commit nor updates the references (ex. in the fastforward case)
-This method does not allow customized parameters for the merge operation, i would like to leave that for a second iteration over this method and let's it work for the moment with the default options defined in the libgit2 constant GIT_MERGE_OPTS_INIT.

The tests i implemented would help to understand this behaviour easily.

Extra: there is also a minor change in the Repository_status method, i removed the args parameter because it wasn't being used anywhere within the method.

[jdavid]

Hello Victor, thanks for contributing.

We have the general policy to wrap git structs, so it should be like:

typedef struct {
    PyObject_HEAD
    git_merge_result *result;
} MergeResult;

Note that Repository_status is "expensive" and may fail. Do not keep it.

And please update the documentation docs/merge.rst

[victorgp]

Thanks @jdavid for your comments.

About the MergeResult struct, you are right, i'll implement it in that way.

[victorgp]

Fixes done, please take a look and tell me if you like them.
Thanks

[jdavid]

Why do you need MergeResult.index?

merge = repo.merge(...)
merge.index

How that is better than:

merge = repo.merge(...)
repo.index

If MergeResult does not keep a reference to the repository, code would be simpler.

[victorgp]

Actually i don't need it but since the git_merge_result struct has an index field, i supposed you also wanted it here.

I'll remove it so it's simpler

[jdavid]

Okey, I missed that. Anyway if you don't need it just remove.

[victorgp]

Index removed!

[alexband]

@victorgp does merge_result has any attributes to indicate this merge is viable? like will it produce conflicts?

there is 'is_fastforward', 'is_up_to_date', but no other identification for whether the merge is viable, (is it can be merged but not fastforward merge?)

[alexband]

sorry I found that merge_result has an index object, that explains