Many editors will notice when a file changes out from under them. Are there any editor that will offer to let you do a three-way merge if you have unsaved edits on the file?
The common scenario for this is I forget to save a file before I so an SVN update and when I switch back to my editor realize that I now have the choice of stomping on the update I just did, discarding my changes, or doing the copy/paste/external-diff-tool song and dance.
Yes I know the correct solution is ctrl+s before I update but I’m human and want a really easy solution to fix the problem after I muck it up.
EditPad Pro, when it detects a file that you have open with unsaved changes has changed on disk, will ask you if you want to reload the file from disk, ignore the change on disk, or see the difference between the file on disk and the version with unsaved changes that you have open.
That is a two-way diff rather than the three-way diff you asked. I don’t know any text editor that will offer to do a three-way diff. If the file on disk has been clobbered, a text editor no longer has a copy of the original. That would be something for version control to solve.
A preventive measure could be to have your editor keep a lock on files that you have open. Then the SVN update will fail on any files you have open in your editor. In EditPad Pro, there’s an option for that in Options, Preferences, Files.