Eh, most of the time you do have to publish it. MIT/BSD/Apache allows you not to, but most big projects are using LGPL or another share-alike license. With those, if you're making a project that you do publish (e.g. a commercial product that uses that library/language/etc.) you do kinda legally have to share that modified source code. It's of course different if you're scripting for your own sake, but the moment you publish anything using them you also have to publish your modified versions of libraries and other stuff.
I do agree with the "fork and make it better for you", but I also think it's common courtesy to throw up issues for the bugs or missing features you encounter, as well as pull requests. If for no other reason then as "prototypes" or "quick fixes" that others can cherry-pick into their own forks. They may get rejected, they may get closed, but you still don't have to sit there arguing about it since you have your own version. From a slightly Kantian angle you have your working version and you've now fulfilled your social duty by offering solutions to problems. You've got no need to campaign for the solutions if they get rejected.
It's virtuous and you get to ignore the github flame wars. There's really no downside beyond taking 5 minutes to be nice and at least put your solution out there. Also fulfills your reciprocal legal duty under LGPL and such.
I think the best way to go (if you're the "Good Samaritan Who Wants to Do His Civic Duty but Also Doesn't Want to End Up Spending the Week in Nerd Court") is to fork it, fix it, and leave a brief comment in the issue thread that says "hey, I fixed this in my fork".
That way, people with the same issue who come in to the issue thread through a search aren't reduced to combing through all the forks to see if one happens to fix the issue. Then instead of spamming up the thread with "me too, this is soo frustrating, fix asap pls", they can spam it up with "merge this fork into the main project asap pls" :-)
If you don't distribute to others you don't need to distribute your own changes even for copyleft licenses. That's why the AGPL license was written, because if you're doing something as a service you won't need to distribute any sources even with GPL license.
> you do kinda legally have to share that modified source code
I'm using the license exactly as intended. Upstream developers literally don't matter. Free software is not about developers, it's about users.
Free software licenses say the user gets the source code. They're about empowering the user, in this case me, with the ability use and modify the software as I see fit. If I customize something for my personal use, then I'm the only user of the fork and license terms are fulfilled. People would only get to demand source code from me if I started distributing compiled executables to other users.
> You've got no need to campaign for the solutions if they get rejected.
I used to feel that need. Caused me significant anxiety. I thought upstreaming patches was the Right Thing to do. Mercifully I've been cured of this misconception.
> There's really no downside beyond taking 5 minutes to be nice and at least put your solution out there.
I have no problem with that. My point is getting involved with upstream is often more trouble than it's worth. Let them do their thing. Just pull from them and rebase your changes. Enjoy life.
People should think twice before trying to cram their unsolicited code down other people's throats. Even when they ask for the code, chances are deep down they don't actually want to deal with it.