Managing multiple Qt versions with Git clone

Like many Qt developers I have many different versions of Qt on one computer. In the past I used to have a copy of nearly every tarball and a built version. My /home/ben/dev directory looked something like this:

...
qt-all-opensource-src-4.5.0/
qt-all-opensource-src-4.5.0.tar.bz2
qt-all-opensource-src-4.5.1/
qt-all-opensource-src-4.5.1.tar.bz2
qt-all-opensource-src-4.5.2/
qt-all-opensource-src-4.5.2.tar.bz2
...

Now that the Qt repository has been open for a while we can take advantage of a nice feature of git clone called local cloning. On my computer I have a primary Qt repository (/home/ben/dev/qt-master/) which has has remotes pointing to my personal Qt fork and the main Qt repository.

Rather then downloading a tarball of 4.5.2 I now do a local clone of Qt and then checkout the tag "v4.5.2". Although Gitorious does not list tags (missing feature?) both Qt 4.5.1 and 4.5.2 have been tagged in the Qt Git repository.

git clone -l qt-master qt-4.5.2
cd qt-4.5.2
git tag -l  # List the available tags I can checkout
git checkout v4.5.2

A local clone will share object files when possible saving you a lot of hard drive space. For Qt versions older then 4.5.1 I still have the tarballs, but going forward there are a lot of advantages to using this beyond saving space. In the past when tracking down a bug in a specific release I have often tweaked the code or applied a patch. Now that the releases are fully backed by Git I can quickly revert back to the release as well as using tools like git blame and git log to get much more information about any files I am investigating. You also get the tests and util directories which are stripped out of releases.

In addition to the releases I also have a clone for the Qt 4.5 branch, what will be 4.5.3. qt-master is the original Git repository which tracks what will become Qt 4.6. After this change I ended up with a directory like this:

...
qt-all-opensource-src-4.5.0/
qt-all-opensource-src-4.5.0.tar.bz2
qt-4.5.1/
qt-4.5.2/
qt-4.5/
qt-master/
...

Like many Qt developers I have written a bash script 'qs' that I have in my shell profile to quickly list and switch between Qt directories.

'qs' - Display current Qt version
'qs ' - List all qt directories
'qs qt-4.5.2' - Swap environment to use Qt 4.5.2
'qcd' - Change to the current Qt's directory

This Git clone trick of course applies to any Git based project, not just Qt, but it is yet another hidden gem of the decision to open the Qt repository.