Tips for upgrading your configuration
From 3.5 to 4.0
The best advice is to start from the default rc.lua and backport any changes you might have added to your rc.lua. This avoids most of the possible errors due to missing important changes.
To do this, you can download the default rc.lua for 3.5.9 here, and then compare your existing rc.lua with the 3.5.9 default using your diff tool of choice. Write down the changes, then apply these to the 4.0 default rc.lua, which you can find at /etc/xdg/awesome/rc.lua after the upgrade, or here if you have not yet performed the upgrade.
If you still wish to ignore this advice, first read the NEWS section about the breaking changes. This document assumes you did.
Be warned, even if it looks like it’s working after changing some lines, it wont supports dynamic screen changes and will have many subtle bugs. The changes mentioned below are important for the stability of your window manager.
Here is a diff of the 3.5.9 rc.lua with the 4.0 one. All changes due to new features and new syntaxes have been removed. A – in front of the line correspond to content of the 3.5 rc.lua and + its replacement in 4.0.
This document does not cover the new features added in the Awesome 4 rc.lua, it only covers the minimal required changes to have a properly behaving config.