How do I clear undo history for the current buffer in Vim?

Explanation

Sometimes you finish a risky refactor and want a clean undo boundary before handing the buffer off or continuing with unrelated edits. Vim can reset the current buffer's undo tree by temporarily setting undolevels to -1 and performing a tiny no-op edit. This is an advanced move, but it is useful when old undo states are no longer meaningful.

How it works

• :let s:u=&l:undolevels stores the current local undo limit
• :setlocal undolevels=-1 tells Vim to drop undo information for the next change
• :execute "normal! a\<BS>\<Esc>" performs a minimal insert/backspace edit to trigger that reset
• :let &l:undolevels=s:u restores your previous undo setting

After this sequence, undo history before the reset point is gone for the current buffer. New edits build a fresh undo chain.

Example

Before reset: 120+ undo entries from an earlier mass rewrite
After reset:  clean undo history starting from the current state

This is especially helpful after huge macro-driven edits where stepping through historical states is noisy and slow.

Tips

• Use this intentionally; you cannot recover discarded undo states afterward
• Prefer buffer-local (setlocal) so you do not affect other open files
• If you rely on persistent undo files, this still resets the in-memory tree for the current buffer session