docs/contribute/git_howto.rst

..  Licensed to the Apache Software Foundation (ASF) under one
    or more contributor license agreements.  See the NOTICE file
    distributed with this work for additional information
    regarding copyright ownership.  The ASF licenses this file
    to you under the Apache License, Version 2.0 (the
    "License"); you may not use this file except in compliance
    with the License.  You may obtain a copy of the License at

..    http://www.apache.org/licenses/LICENSE-2.0

..  Unless required by applicable law or agreed to in writing,
    software distributed under the License is distributed on an
    "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
    KIND, either express or implied.  See the License for the
    specific language governing permissions and limitations
    under the License.

.. _git-howto:


Git Usage Tips
==============

Here are some tips for git workflow.

## How to resolve conflict with master

- First rebase to most recent master

.. code:: bash

  # The first two steps can be skipped after you do it once.
  git remote add upstream [url to tvm repo]
  git fetch upstream
  git rebase upstream/master


- The git may show some conflicts it cannot merge, say `conflicted.py`.

  - Manually modify the file to resolve the conflict.
  - After you resolved the conflict, mark it as resolved by

.. code:: bash

  git add conflicted.py

- Then you can continue rebase by

.. code:: bash

  git rebase --continue

- Finally push to your fork, you may need to force push here.

.. code:: bash

  git push --force


How to combine multiple commits into one
----------------------------------------

Sometimes we want to combine multiple commits, especially when later commits are only fixes to previous ones,
to create a PR with set of meaningful commits. You can do it by following steps.

- Before doing so, configure the default editor of git if you haven't done so before.

.. code:: bash

  git config core.editor the-editor-you-like

- Assume we want to merge last 3 commits, type the following commands

.. code:: bash

  git rebase -i HEAD~3

- It will pop up an text editor. Set the first commit as `pick`, and change later ones to `squash`.
- After you saved the file, it will pop up another text editor to ask you modify the combined commit message.
- Push the changes to your fork, you need to force push.

.. code:: bash

  git push --force


Reset to the most recent master
-------------------------------

You can always use git reset to reset your version to the most recent master.
Note that all your ***local changes will get lost***.
So only do it when you do not have local changes or when your pull request just get merged.

.. code:: bash

  git reset --hard [hash tag of master]


Recover a Previous Commit after Reset
-------------------------------------
Sometimes we could mistakenly reset a branch to a wrong commit.
When that happens, you can use the following command to show the list
of recent commits

.. code:: bash

   git reflog

Once you get the right hashtag, you can use git reset again to change
the head to the right commit.


Apply only k-Latest Commits on to the master
--------------------------------------------

Sometimes it is useful to only apply your k-latest changes on top of the master.
This usually happens when you have other m-commits that are already merged
before these k-commits. Directly rebase against the master might cause merge conflicts
on these first m-commits(which are can be safely discarded).

You can instead use the following command

.. code:: bash

  # k is the concrete number
  # Put HEAD~2 for the last 1 commit.
  git rebase --onto upstream/master HEAD~k

You can then force push to the master. Note that the above command will discard
all the commits before tha last k ones.


What is the consequence of force push
-------------------------------------

The previous two tips requires force push, this is because we altered the path of the commits.
It is fine to force push to your own fork, as long as the commits changed are only yours.