When I\'m writing code in intellij and make an errors, it highlists code with erros, when I put mouse over it, it displays detailed error message. The problem is I can\'t co
The issue is now fixed.
I've tested it with Intellij IDEA 2017.1.4 and it's working just fine :
Holding CTRL key seemed to do the trick then I could select the description and copy.
UPDATE: It works via Alt+Click in the current IDE versions, but there are still several usability issues: it's not discoverable, doesn't work for all the pop-ups and may copy additional text/keyboard shortcut symbols. There is also a request to make it more straightforward by allowing to copy only selected text via Ctrl+C.
Original answer:
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I can't select text from the error message tooltip at all on Mac and IntelliJ CE 2018, but someone in the linked bug ticket pointed out that Alt + Mouse Click copies the text to the clipboard (meaning you can then paste and get the text) and that worked for me.