gem update behavior with no argument

I've always found gem update to be a command that was easy to misuse. Earlier today I was looking at an issue with gem outdated being unaware of ruby version constraints, and ran gem update --explain (which seems to be broken?) for comparison. I wasn't using trunk at the time, and, it was off and running trying to update everything, starting with a default gem.

Granted, it was a mistake, and code can only go so far in terms of stopping mistakes, but I think you know what I mean. Worse, new users might not even know what it did, what effects it would have, etc.

I'm sure gem update existed long before there were 'default gems' (thanks to @hsbt for all his work on them), so maybe it's time to change the behavior of it with respect to default gems?

Also, I've seen other issues about considering bundled gems, --user-install gems, etc.

Generally, what I'm proposing is that gem update does nothing without a gem name or additional parameters. Obviously, changes may be breaking,

This issue is related to:

• Network problems
• Installing a library
• Publishing a library
• The command line gem
• Other

Here are my current environment details:

NA

I will abide by the code of conduct.