Struct History 

pub struct History { /* private fields */ }

Whole-content undo history, stored as rope snapshots.

A snapshot is a Rope rather than a String because ropey clones are O(1) and copy-on-write: two snapshots share every node they have in common, so a deep undo stack over a large file costs the edits, not one full copy of the text per step. to_string() would allocate and copy the whole buffer on every keystroke.

Whole-content snapshots stay the right call at this size — they are correct for any edit shape, and with structural sharing they are no longer expensive enough to justify per-edit deltas.

Runs have no clock. VS Code and Zed break undo groups on an idle timer. A timer means the buffer needs a clock, which means tests need to inject one, which means the rule is only ever exercised through a fake. The rule here is structural instead: consecutive edits of the same EditKind coalesce, and anything that is not an edit — a motion, a click, a save — calls boundary. That is deterministic and it matches what a user means by “undo what I just typed”: the run ends when they moved.

ponytail: pausing mid-word for ten minutes without moving still coalesces. If that ever bites, a timer goes beside this rule, not instead of it.

Implementations

impl History

pub fn record(&mut self, kind: EditKind, before: Rope, selections: &Selections)

Record the state before an edit, unless it continues the open run.

Continuing a run means not pushing: the snapshot already on the stack predates the whole run, which is exactly the state undo should restore.

pub fn boundary(&mut self)

End the open run, so the next edit starts a new undo step.

Called on anything that is not an edit — a motion, a click, a save.

pub fn undo( &mut self, current: Rope, selections: &Selections, ) -> Option<Snapshot>

Returns the state to restore, banking current for redo.

pub fn redo( &mut self, current: Rope, selections: &Selections, ) -> Option<Snapshot>

Trait Implementations

impl Default for History

fn default() -> History

Returns the “default value” for a type.