Getting Started with Modular Boost Library Maintenance

This page describes the mechanics of maintaining a Boost library using Git and Modular Boost. The intended audience is developers involved in the maintenance of existing Boost libraries.

The Big Picture

Library maintenance occurs in the context of how Boost repositories are organized. Please study the Modular Boost Overview before continuing, since a Boost developer needs to be familiar with how Boost organizes its repositories.

The examples given on this page follow Boost recommended workflow practices, but keep workflow discussion simple for this introduction. If you feel you need to better understand workflow recommendations and rationale before continuing, feel free to read Modular Boost Library Workflow Overview.

Prerequisites

• A recent release of the Git command line client installed. See Getting Started with Git.
• A (free) ​GitHub account. See Getting Started with GitHub.
• A compiler and development environment installed and working smoothly.
• Modular Boost installed as described in Getting Started with Modular Boost.
• b2 in your path. That allows most of the command line examples given here to work as shown on both Windows and POSIX-like systems.

Getting started

The preferred development environment is usually for the library being worked on have a development branch checked out, while Boost super-project and other libraries remain on the master branch.

Checking out the development branch

You can see what branch mylib is currently on like this:

cd modular-boost/libs/mylib
git branch

Then if you need to change the branch to a development branch such as develop, do this:

cd modular-boost/libs/mylib
git checkout develop

You only have to do that once; your local repo working copy will sit on the branch until it is explicitly changed by a command you give.

Of course, you don't have to change the directory before every command, and from here on this tutorial will assume the directory has not been changed since the prior example.

If there is any possibility the branch head content in the public upstream repo has changed, you also will want to update content:

git pull

Typical maintenance tasks

Testing locally

pushd test
b2
popd

Checking status

Before making changes, it is a good idea to check status. Here is what that looks like on Windows; the message you get may vary somewhat:

>git status
# On branch develop
nothing to commit, working directory clean

Fix a simple bug

For simple bugs, particularly in projects with a single maintainer, it is common practice to fix bugs directly in the develop branch. Creating a test case with your favorite editor, testing the test case, fixing the bug, testing the fix, and then iterating if necessary is no different than with any programming environment.

Once the fix is complete, you then commit the fix locally and push from your local repo up to your public boostorg repo on GitHub. These same commands would be used for any Git project, modular or not, so hopefully you are already somewhat familiar with them:

cd modular-boost/libs/mylib
git commit -a -m "my bug fix"
git push

Fix a bug using a bug-fix branch

Fixing a bug directly on the develop branch is fine, if that's the library's policy, but if the bug is messy, multiple maintainers are involved, interruptions are expected, or other complexities are present, then it is better practice to work on the bug in a separate bug-fix branch.

git checkout -b bugfix/complex-boo-boo

This creates the branch bugfix/complex-boo-boo, and switches to it. Incidentally, bugfix/ is part of the name, not a directory specifier. The new branch is based on branch develop because the working copy was on branch develop at the time of the branch.

Since the bug is complex, it may take some time to fix and may go through several cycles of fixes, tests, and commits.

Once the bug is fixed and a final commit is done, then it is time to merge the bugfix/complex-boo-boo branch back into develop:

git checkout develop
git merge bugfix/complex-boo-boo
git push

The usual practice is to delete temporary branches like bugfix/complex-boo-boo once they have been merged:

git branch -d bugfix/complex-boo-boo

Start work on a new feature

Developers are encouraged to create a (possibly private) branch to work on new features, even simple ones, since development of new features on the develop branch might leave it unstable for longer that expected. Using the Git Flow convention, the branch will be named feature/add-checksum-option.

git checkout develop
git checkout -b feature/add-checksum-option

When you create the branch, or perhaps later, you may decide the branch should be public (i.e. be present in the library's public boostorg repo) so that you can share the branch with others or just to back it up. If so, set that up by running:

git push --set-upstream origin feature/add-checksum-option

Whether or not --set-upstream origin bugfix/complex-boo-boo is actually needed depends on the branch.autosetupmerge configuration variable that isn't discussed here. If you don't supply --set-upstream origin bugfix/complex-boo-boo on your first push and it turns out to be needed, you will get an error message explaining that.

The usual cycle of coding, testing, commits, and pushes (if public) then begins. If other work needs to be done, a stash or commit may be done to save work-in-progress, and the working copy switched to another branch for awhile. If significant fixes or other enhancements have been made to develop over time, it may be useful to merge develop into the feature branch so that the eventual merge back to develop has less conflicts. Here is how the merge from develop to feature/add-checksum-option is done:

git checkout feature/add-checksum-option
git merge develop

First post-svn conversion merge to master

When you are ready to merge the develop branch to master (or better yet a release branch that's branched off master), there's a bit of housekeeping to be done the first time after the conversion from svn so that future merges proceed smoothly. We're going to create a merge point between the develop and master branches so that Git knows the last point the two branches were in synch. Once we've done that Git will perform a merge by replaying the commits on develop on top of master, starting from the last known merge: in other words Git will perform the tricky stuff of figuring out what to merge for us.

Begin by navigating to the history for your library on Github, starting with branch master, for example the Config library ​can be seen here. Looking down through the commit history we can see that the last merge (In SVN land) was on October 25th 2013: make a note of that date. Now use the dropdown box to change the history to point to the develop branch, ​Config library can be seen here. As you can see there have been several commits since the date above, the last before that date was on Oct 21st, click on the commit message for that change to take you to the actual diff for that change, ​in our example here. The SHA1 for that commit is shown below and to the right of the commit message, in this case it's 67f6b934f161dc5da2039004986a14d9217afae4.

Now we'll create a merge to the specific commit, begin by changing your library to the master branch:

git checkout master

Now create a merge to the specific commit above; since we don't really want to actually change the master branch we'll use the -s ours option to avoid any conflicts:

git merge --no-ff --no-commit -s ours 67f6b934f161dc5da2039004986a14d9217afae4

You can now use git status and git diff to check for modifications, in this case there are none. Now make the commit:

git commit -am "Create first merge point for Git"

And finish off by pushing your changes to Github

git push

Then navigate to your libraries history again, and check that the merge shows up, ​our config example is here. You're now ready for "routine" merges to proceed as per Gitflow (or whatever other strategy you wish to use).

Lightweight library release

Small, simple libraries and simple releases just merge develop into master, tag master, and declare victory.

git checkout master
git merge --no-ff develop
git tag -a 1.56.1

Heavyweight library release

Large, complex libraries, particularly those with multiple developers working in parallel, need to use a release procedure that scales up better than the lightweight procedure. The Git Flow approach is recommended. Find out more at Modular Boost Library Workflow Overview and be sure to study the examples given in ​Vincent Driessen's original blog posting.