Reproduction:
Bug 457401

Actual result:
- No "Print" icon on toolbar
- Menu item "Print invoice" is disabled, but nothing tells me why. The obvious guess is that the print system is misconfigured. I use KDE, so I hunt the GNOME print config. No Gnome control center on my system. Ask on #gnucash. Nobody knows why. Finally, I find out by accident (Print is enabled in account statements window) that my print setup is fine (although I have no printer, but I can always print to PostScript / PDF, as expected). GnuCash wanted me to "post" the invoice first before it allows me to print it, but nothing tells me. No way for me to find out.

Expected result:
When some action cannot be performed, it is obvious why.
In cases like this, e.g. enable the menu item and show a dialog which tells:
- Why it cannot be performed now
- Why that restriction exists
- How I can solve it

Note that a tooltip is not sufficient, because the tooltip only shows when I hover over the menu item or toolbar button. But I a) never hover over it in the first place, because I see it's disabled so I don't even go there with the mouse and b) even if I tried to click it, I would not rest the mouse there and stare at the screen for 1-2 seconds. More theoretically, a tooltip is a nice extra feature that should not be re lied upon, and it typically explains what something is, not why it's disabled. Given that I know what "print" is, it didn't occur to me to try the tooltip, so even if one was added, it would not help at all.