Apply inversions to Views on undo/redo

When using undo/redo, the history revision can be decremented. In that
case we should apply the inversions since the given revision in
History::changes_since. This prevents panics with jumplist operations
when a session uses undo/redo to move the jumplist selection outside
of the document.

1 files changed, 14 insertions, 10 deletions

diff --git a/helix-core/src/history.rs b/helix-core/src/history.rs
index 697f29b4..5f9fa71e 100644
--- a/helix-core/src/history.rs
+++ b/helix-core/src/history.rs
@@ -122,17 +122,21 @@ impl History {
     /// 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;
-        }
+        use std::cmp::Ordering::*;
 
-        // 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))
+        match revision.cmp(&self.current) {
+            Equal => None,
+            Greater => self.revisions[self.current + 1..=revision]
+                .iter()
+                .map(|revision| &revision.inversion)
+                .cloned()
+                .reduce(|acc, inversion| acc.compose(inversion)),
+            Less => self.revisions[revision + 1..=self.current]
+                .iter()
+                .map(|revision| &revision.transaction)
+                .cloned()
+                .reduce(|acc, transaction| acc.compose(transaction)),
+        }
     }
 
     /// Undo the last edit.