I don't know where to file an issue against the CLA, so just doing it here.

CLA's are a barrier to contribution, with many hackers wary that they are granting too much to the receiving company.

After reading the CLA multiple times, I only think I understand what it is doing. It helps that I have read many documents of this kind over years. I expect most people will not understand the CLA, and not understanding makes people afraid.

The CLA does include some lay-explanation at the top:

This license is for your protection as a contributor as well as the protection of PingCAP and its other contributors and users; it does not change your rights to use your own Contributions for any other purpose.

This is a good start, but I think it explains the opposite of what contributors are concerned about. Maintaining the rights to my contributions is usually meaningless, as they are useless without the larger program. What contributors care about is PingCAP's rights.

I believe the things that people are most worried about is the company taking unexpected advantage of their contributions for profit, particularly by relicensing their contributions to a more restrictive license. Relicensing open source software is usually controversial, relicensing to a more restrictive licenese especially so. I have seen one contributor ask for clarification on exactly this point.

Of course, the great benefit of a CLA is that it makes a benevolent relicense much easier. It would be extremely hard, e.g. to relicense Rust at this point (and it needs to be).

The text dealing with this is:

Grant of Copyright License. Subject to the terms and conditions of this CLA, You hereby grant to PingCAP and to recipients of software distributed by PingCAP a perpetual, worldwide, non-exclusive, no-charge, royalty-free, irrevocable copyright license to reproduce, prepare derivative works of, publicly display, publicly perform, sublicense, and distribute Your Contributions and such derivative works.

The word "sublicense" here I think is - to contributors - the most important part of the document. I believe it means that PingCAP can relicense the work to any license they want.

If so it would be more forthcoming for the intro paragraph to explicitly state something like, "This license does not change your rights to use your own Contributions for any purpose. This license does allow PingCAP to relicense or otherwise use your contribution for any purpose."

Note: I am filing this after discovering that pingcap/talent-plan, a modest project likely without any valuable intellectual property, requires the CLA. Parts of talent-plan may also be derivative works. I haven't thought about how that interacts with the CLA, but it does limit what PingCAP can do with the project.