In many distributed development scenarios, it isn’t always feasible for developers to share task branches by advertising their URLs. For example, a developer working on a laptop might take it home overnight so his/her task branches could well be inaccessible when a gatekeeper in another timezone wants to review or merge it.
Bazaar provides a neat feature to assist here: merge directives.
Understanding merge directives
You can think of a merge directive as a “mini branch” - just the new growth on a branch since it was created. It’s a software patch showing what’s new but with added intelligence: metadata like interim commits, renames and digital signatures.
Another useful metaphor is a packet cake: a merge directive has a recipe together with the ingredients you need bundled inside it. To stretch the metaphor, the ingredients are all the metadata on the changes made to the branch; the recipe is instructions on how those changes ought to be merged, i.e. information for the merge command to use in selecting common ancestors.
Regardless of how you think of them, merge directives are neat. They are easy to create, suitable for mailing around as attachments and can be processed much like branches can on the receiving end.
Creating a merge directive
To create and optionally send a merge directive, use the send command.
By default, send will email the merge directive to the “submission address” for the branch, which is typically the lead developer or the development mailing list. send without options will create a merge directive, fire up your email tool and attach it, ready for you to add the explanatory text bit. (See the online help for send and Configuration Settings in the User Reference for further details on how to configure this.)
Most projects like people to add some explanation to the mail along with the patch, explaining the reason for the patch, and why it is done the way it is. This gives a reviewer some context before going into the line-by-line diff.
Alternatively, if the --output (or -o) option is given, send will write the merge directive to a file, so you can mail it yourself, examine it, or save it for later use. If an output file of - is given, the directive is written to stdout. For example:
cd X-fix-123 bzr send -o ../fix-123.patch
Applying a merge directive
Merge directives can be applied in much the same way as branches: by using the merge and pull commands.
They can also be useful when communicating with upstream projects that don’t use Bazaar. In particular, the preview of the overall change in a merge directive looks like a vanilla software patch, so they can be applied using patch -p0 for example.