Just to be clear, I put the question to FSF directly. I got permission from Brett to post his reply. You'll find it below:
On Sun, 2008-02-10 at 13:01 -0500, Alan Wood via RT wrote:
> The crux of the issue is that although the library is written in Java and
> your foundation's stance on Java is that the LGPL is 100% compatible with
> not shipping final source upon the use of it, MyGWT is meant to be used with
> a Java based toolkit called GWT. This GWT reads java source and cross
> module that gets transmitted to the client and runs in the web browser. The
> argument is that when GWT does this, it creates a derivative work of the
> library and thus requires that the module created be shipped with source so
> that the GWT can in fact be used again to create a new version of the module
> with an altered version of the library.
I think the argument you've laid out here is basically correct.
In the terms that LGPLv3 uses, MyGWT is the Library, software that
developers build on top of it is an Application (in the usual case), and
hosting it on their servers need to follow the conditions for doing so
set forth in section 4 of LGPLv3.
In order to comply with the requirement in section 4(d), it does seem
like those developers need to provide Minimal Corresponding Source and
Corresponding Application Source, as allowed in section 4(d)0. Using a
suitable shared library mechanism, as allowed in section 4(d)1, does not
seem to be possible here: it doesn't look like GWT has any capability to
make use of libraries that are already installed on a user's system.
I hope this helps you understand where these requirements are coming
from. If you have any further questions, or think I may have
misunderstood something about GWT, please feel free to get in touch.
Licensing Compliance Engineer, Free Software Foundation