Difference between revisions of "Git tips"

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(Start the Git tips page)
 
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=== How to push changes ===
 
=== How to push changes ===
  
The important thing to realize is that when pushing changes to the remote server (aka "''origin''"), your changes '''''must''''' be based on the remote server. Subversion allowed you, in some cases, to commit without having the most up-to-date working copy. Git doesn't.
+
The important thing to realize is that when pushing changes to the remote server (aka "''origin''"), your changes '''''must''''' be based on the remote repository. Subversion allowed you, in some cases, to commit without having the most up-to-date working copy. Git doesn't.
  
TODO
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A normal ''git push'' without any errors is one that only adds new commits, that (in their metadata) point to existing commits.
 +
 
 +
If you try to push local commits when the ''origin'' has commits you do not have, you will get an error similar to this:
 +
 
 +
To git@github.com:scummvm/scummvm.git
 +
  ! [rejected]        master -> master (non-fast-forward)
 +
error: failed to push some refs to 'git@github.com:scummvm/scummvm.git'
 +
To prevent you from losing history, non-fast-forward updates were rejected
 +
Merge the remote changes before pushing again.  See the 'Note about
 +
fast-forwards' section of 'git push --help' for details.
 +
 
 +
This fix this problem, we need to fetch the remote commits we do not have, and then either "put" our new commits on top of the remote repository's, or create a new "merge commit" that combines the remote repository's commit and yours.
 +
 
 +
Let's introduce several related commands:
 +
* '''git fetch''' — Retrieves commit objects from the remote repository. You can always run this command without fear. It doesn't modify any of your local changes.
 +
* '''git merge''' — Creates a "merge commit" from 2 or more branches. If only one branch diverges from the root, it will perform a "fast-forward" and no merge commit will be created. (This is configurable).
 +
* '''git rebase''' — Moves (i.e. reapplies) a series of commits onto a different base.
 +
* '''git pull''' — Perform a ''fetch'' followed by a ''merge'' (the default behavior) or ''rebase'' (with a flag).
 +
 
 +
So in our case, if we made a few unrelated commits, we just want to apply them on top of the remote commits, and to do that wen can use <tt>git pull --rebase</tt> which will get the remote changes, and re-apply our local changes on top of the remote's. From that state, we could <tt>git push</tt> our changes back up.
  
 
=== Branchy development ===
 
=== Branchy development ===
  
 
TODO
 
TODO

Revision as of 17:19, 12 February 2011

The following is a list of tips, do's and dont's for working with the ScummVM git repositores, compared to working with Subversion.

Organization

Development is done on the master branch, which is equivalent the the old Subversion trunk. Release branches are branched from, and merged to, master. Tags are always annotated (git tag -a) in order to include a timestamp.

Dont's

  • Never ever use git push -f without discussing it on the mailing-list. That operation deletes commits from the server, and will cause problems to others working with the repository.
  • Try to not create pointless merge commits. This will be explain in the #Workflow section. If you do make merge commits, the branch you're merging should include commits that are "bunched together" on purpose. This makes them easier to review or revert.

Workflow

There are several ways to work with git. Here we'll discuss two: You could make your commits on the master branch, or you could make them on a separate branch, called a topic branch and then merge them into the master branch, before pushing. We'll cover the basics of pushing first

How to push changes

The important thing to realize is that when pushing changes to the remote server (aka "origin"), your changes must be based on the remote repository. Subversion allowed you, in some cases, to commit without having the most up-to-date working copy. Git doesn't.

A normal git push without any errors is one that only adds new commits, that (in their metadata) point to existing commits.

If you try to push local commits when the origin has commits you do not have, you will get an error similar to this:

To git@github.com:scummvm/scummvm.git
 ! [rejected]        master -> master (non-fast-forward)
error: failed to push some refs to 'git@github.com:scummvm/scummvm.git'
To prevent you from losing history, non-fast-forward updates were rejected
Merge the remote changes before pushing again.  See the 'Note about
fast-forwards' section of 'git push --help' for details.

This fix this problem, we need to fetch the remote commits we do not have, and then either "put" our new commits on top of the remote repository's, or create a new "merge commit" that combines the remote repository's commit and yours.

Let's introduce several related commands:

  • git fetch — Retrieves commit objects from the remote repository. You can always run this command without fear. It doesn't modify any of your local changes.
  • git merge — Creates a "merge commit" from 2 or more branches. If only one branch diverges from the root, it will perform a "fast-forward" and no merge commit will be created. (This is configurable).
  • git rebase — Moves (i.e. reapplies) a series of commits onto a different base.
  • git pull — Perform a fetch followed by a merge (the default behavior) or rebase (with a flag).

So in our case, if we made a few unrelated commits, we just want to apply them on top of the remote commits, and to do that wen can use git pull --rebase which will get the remote changes, and re-apply our local changes on top of the remote's. From that state, we could git push our changes back up.

Branchy development

TODO