It looks like there is an unintended consequence of the Apache License 2.0 of allowing a company to patent some functionality, and the only way to acquire that patent is to keep your implementation as a close fork of the original derived work. The question is, whether or not the patent grant for just using swift (downloading and running it), can cover other development work that is not associated with swift. If not then Apache License 2.0 actually seems to paradoxically reinforce the situation it is trying to avoid by tying implementation and copyright directly to patents, thereby boosting patents as a way to squash other open source projects. Any comment by an Apache person would be greatly appreciated.
>3. Grant of Patent License. Subject to the terms and conditions of this License, each Contributor hereby grants to You a perpetual, worldwide, non-exclusive, no-charge, royalty-free, irrevocable (except as stated in this section) patent license to make, have made, use, offer to sell, sell, import, and otherwise transfer the Work, where such license applies only to those patent claims licensable by such Contributor that are necessarily infringed by their Contribution(s) alone or by combination of their Contribution(s) with the Work to which such Contribution(s) was submitted. If You institute patent litigation against any entity (including a cross-claim or counterclaim in a lawsuit) alleging that the Work or a Contribution incorporated within the Work constitutes direct or contributory patent infringement, then any patent licenses granted to You under this License for that Work shall terminate as of the date such litigation is filed.
Apple is a Contributor. They have given a patent grant on their contributions. If they didn't contribute something to Swift and they sue Swift other contributors for making a patent violation or their non-contributions, then all patent grants for Apple disappear and other contributors can sue Apple for anything that Swift uses that was patented.
