Apply transactions to all views (#4733)

* Add a test case for updating jumplists across windows

* Apply transactions to all views on history changes

This ensures that jumplist selections follow changes in documents, even
when there are multiple views (for example a split where both windows
edit the same document).

* Leave TODOs for cleaning up View::apply

* Use Iterator::reduce to compose history transactions

Co-authored-by: Blaž Hrastnik <blaz@mxxn.io>

Co-authored-by: Blaž Hrastnik <blaz@mxxn.io>

1 files changed, 17 insertions, 1 deletions

diff --git a/helix-core/src/history.rs b/helix-core/src/history.rs
index 51174c02..697f29b4 100644
--- a/helix-core/src/history.rs
+++ b/helix-core/src/history.rs
@@ -54,7 +54,7 @@ pub struct History {
 }
 
 /// A single point in history. See [History] for more information.
-#[derive(Debug)]
+#[derive(Debug, Clone)]
 struct Revision {
     parent: usize,
     last_child: Option<NonZeroUsize>,
@@ -119,6 +119,22 @@ impl History {
         self.current == 0
     }
 
+    /// Returns the changes since the given revision composed into a transaction.
+    /// Returns None if there are no changes between the current and given revisions.
+    pub fn changes_since(&self, revision: usize) -> Option<Transaction> {
+        if self.at_root() || self.current >= revision {
+            return None;
+        }
+
+        // The bounds are checked in the if condition above:
+        // `revision` is known to be `< self.current`.
+        self.revisions[revision..self.current]
+            .iter()
+            .map(|revision| &revision.transaction)
+            .cloned()
+            .reduce(|acc, transaction| acc.compose(transaction))
+    }
+
     /// Undo the last edit.
     pub fn undo(&mut self) -> Option<&Transaction> {
         if self.at_root() {