Editora 0.9.10. Archived, so links from that release keep working. Read the 0.18.5 page →
Diff: Compare With…
diff.compareWith Diff the current file against another file you pick.
How to run it
Open the command palette (M-x in the Emacs keymap) and search for Diff: Compare With…, then press Enter. It has no default keybinding, but you can bind one in Settings → Keymaps.