Typically I'd leverage 2 large monitors and keep at least 3 editor "views" into code open at once: one for what I was actively working on and 2 others that would contain reference code. You also take considerable care as to how you organize the code, so that grepping for definitions is easy. If I needed to see how a particular object or function worked, I'd pull it up in one of the auxiliary code windows - which would typically start with a grep alias command that would have a shortcut to open it in a designated emacs buffer window. Not anywhere near as convenient as an LSP but it got the job done.
Typically I'd leverage 2 large monitors and keep at least 3 editor "views" into code open at once: one for what I was actively working on and 2 others that would contain reference code. You also take considerable care as to how you organize the code, so that grepping for definitions is easy. If I needed to see how a particular object or function worked, I'd pull it up in one of the auxiliary code windows - which would typically start with a grep alias command that would have a shortcut to open it in a designated emacs buffer window. Not anywhere near as convenient as an LSP but it got the job done.