Is it possible to distinguish it from an "honest" on_load that happens when a file is opened for real?
In my plugin I want to typecheck loaded files, so that the user instantly gets error highlighting and other good stuff. It's usually 1-2s of background work, so it's not a problem at all.
Except when I use goto anything. Then simply typing a name of the file I want might produce a bunch of file previews, each of them potentially triggering a typecheck. Now that might be a problem.