Google's contention has always been that there is no such thing as a personal project. You can fill out a form to officially get permission to have a "personal project", however, but I doubt many people want to deal with the bureaucracy.
You will notice 6 missing years in commits to my personal github. That is why. Every "personal project" I did ended up in the Google repository instead.
How do they justify that belief? If something is done outside of work hours, not using a work computer, then how would they have any claim over it whatsoever?
It is a widely held belief that writing computer code is an intellectual and creative endeavour (IIRC codified so in European law or something†), therefore it is not tied to a specific timeframe within which you work: you are very much able to think about and solve a work problem under your shower, that's why the corresponding intellectual property of that solution is owned by the company you work for, independent of the time of day you thought about it.
So to cover that, typically law basically defaults on granting your company IP rights on anything you create anytime while you're an employee, and should there be need to challenge that, it's up to you to uphold in court that project X has nothing to do with your company business or tech, or to ensure beforehand that your contract has special provisions granting you IP rights in known situations.
† At the very least this is also the basis as to why software is not patentable in EU, unless they are an integral part of a very concrete process that itself solves an issue (e.g say you invent an industrial process that allows you to synthesize molecule X more efficiently, and that process involves a bit of code as an integral and required part of said process because it is deeply tied to it in a fundamental way, then that precise bit of software can be covered by the patent of the process)
To extend let's change the field a bit: Imagine you are a scientist working in a lab, employed to develop new technologies. One day you're falling in the shower and scribble an idea for a flux capacitor. Could you patent it? Or the company? What if it happens in the office? If that makes a difference: How to prove? Most employment contracts (at least the ones I have seen) make the assumption clear, that all results of "software development" are treated as work for the company. Many companies than have ways to allow hobby projects info uelds different from the actual work (while that definition is quite unspecific and has to be decided case by case)
From what I have seen, a lot of companies have very restrictive IP clauses in employment contracts (at least here in IE).
The first draft of my current contract wanted a claim to all creative work produced, at all hours, on any equipment, in any medium. (e.g. the copyright on a photo I took on holiday would technically have been owned by my employer.)
They also wanted me to give up all "moral rights" which meant I could not say I created anything I did while being employed, and more worryingly, I could not say I didn't create something that the company said I did.
So if you do some volunteer work on a weekend for the web site for a non-profit (say a community center you're a member of). Does that mean that Google doesn't allow that? Does this clause cover any creative work (such as a unique desk that you designed for your home lab)?
This is surprisingly normal. A majority of programmers have contracts that vaguely specify ownership over everything you produce. It's why "personal github as CV" is such a terrible idea.
Interesting. By that do you mean that you chose to release your personal projects under Google or that your personal projects were useful to Google and hence you got their official blessing on them?
There is a clause in the work contract that claims that Google has ownership of all your IP relating to Google's current or planned businesses. Given that it's Google, that's... a very broad category.
You can apply (the process is described on the same website as TFA) to have Google declare that a certain project definitely is not one of their businesses and therefore not covered. You could also make your own judgment, but (having talked to a lawyer about this when considering a Google offer) my impression is that that is a very bad idea and you should go through the process.
(I only know about the US-but-not-California version of the contract; it might be different in other jurisdictions.)
I think that laws should feature these extremelly large fines to companies for keeping clauses in contract that are already known to be in conflict with existing laws.
A very large number of contracts will be so much better and more slim, and a lot of people will not be harrassed by scare tactics.
You will notice 6 missing years in commits to my personal github. That is why. Every "personal project" I did ended up in the Google repository instead.