My opinions are quite clear on this, as evidenced by my Twitter feed. The story and arguments are evolving quite constantly, so I don’t have any intention to boil everything down to a single post at this time.
But let’s put aside the what-makes-a-derivative-work argument, and stick to what’s quite obvious: If Thesis incorporated WordPress code that is licensed under the GPL, it is clearly a derived work violating the GPL by not in turn being licensed GPL.
I’m not talking about using the WordPress functions and classes. I’m not even going to make the argument that all themes derive not only from the WordPress functions they utilize, interact with, and are built on top of, but that in many cases they derive directly from the original default theme.
I’m talking about actually taking GPL code from WordPress code and modifying it. It’s a textbook violation of the GPL, one no one can argue. Some are trying to argue “fair use” and well, that’s absurd, but that’s not what I am aiming to address here.
Thesis 1.8 is currently 9,000 lines of PHP. (WordPress is 200,000.) I spent my evening yesterday skimming each line, and some sections looked familiar. Honestly, I felt crushed. Having made my accusations clear on Twitter, I wanted to back it up.
Even better, let’s go to Thesis’ own inline documentation.
* This function is mostly copy pasta from WP (wp-includes/media.php),
* but with minor alteration to play more nicely with our styling.
This isn’t even a debate anymore.
Update (July 19): You should read Mark Jaquith’s post, Why WordPress Themes are Derivative of WordPress. This is an excellent summation of the opinions of the core team and the issue of whether themes are derivative works.