Why is the GNU GPL v3 compatible with the Apache License v2.0?

Question

I understand that the GNU GPL v2 and Apache License v2.0 are considered incompatible. The FSF's License List explains that this is "because [Apache] has some requirements that are not in that GPL version. These include certain patent termination and indemnification provisions." This seems to be referring to sections three (patent license termination upon litigation) and nine (must hold Contributors harmless when providing a warranty).

In the GPL, section 7 seems to cover the indemnification issue by allowing you to supplement the GPL with a term "Requiring indemnification of licensors and authors of [added] material by anyone who conveys the material".

However, I don't see anything that addresses the patent termination issue. How is the GPL v3 compatible with Apache v2.0's patent license (and license termination) scheme?

Answer 1

According to GPLv3's third-draft rationale document:

The GPLv3 compatibility of the Apache license patent termination clause was accomplished in Draft 3 by the second specific example of an impermissible further restriction given in the third paragraph of section 10.

Looking at GPLv3, this specific example reads

you may not initiate litigation (including a cross-claim or counterclaim in a lawsuit) alleging that any patent claim is infringed by making, using, selling, offering for sale, or importing the Program or any portion of it.

Which means that, should someone engage in the sort of patent lawsuit described in Apache2 against the conveyor of code under GPLv3, the plaintiff's GPLv3 licence - including the patent licence in s11 - would terminate under s8 paragraph 1. Thus, they do appear to be compatible.

Answer 2

Apache's position is that their v2.0 license is compatible with GPL v3.0 but only in the forward direction. That is, you can embed Apachev2-licensed software in GPL v3.0 licensed projects, but not the other way around.