In the text editing view of Eclipse, there is a vertical bar to the right of the scroll bar. It has little colored markings corresponding to lines of the file with errors/warnings/notes, and you can click the markings (or anywhere on it) to jump to that line. Also when you click a symbol, white or light gray markings light up on the bar corresponding to instances of the symbol in the file.
What is this vertical bar thing called?
(I would screenshot it, but it is not working on my system which is why I’m trying to find the name of it, so that I can search for a solution as to why it seems to have disappeared)
In “Window : Preferences : General : Edtors : Text Editors : Annotations” it’s called the “overview ruler”.
Also in this javadoc.
This bug report indicates that there is a hidden, unsettable, preferences option to turn it off. Might have happened to you.