From 8e49f7a2d7e698d00bc7dcf41adf2e7772b13a5f Mon Sep 17 00:00:00 2001
From: Michael Davis <mcarsondavis@gmail.com>
Date: Wed, 23 Nov 2022 09:35:07 -0600
Subject: [PATCH] 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.
---
 helix-core/src/history.rs   | 24 ++++++++++++++----------
 helix-term/src/ui/editor.rs |  2 +-
 2 files changed, 15 insertions(+), 11 deletions(-)

diff --git a/helix-core/src/history.rs b/helix-core/src/history.rs
index 697f29b4ec982..f02e648b403eb 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;
+        if revision == self.current {
+            None
+        } else if revision > self.current {
+            self.revisions[self.current..revision]
+                .iter()
+                .map(|revision| &revision.inversion)
+                .cloned()
+                .reduce(|acc, inversion| acc.compose(inversion))
+        } else {
+            self.revisions[revision + 1..=self.current]
+                .iter()
+                .map(|revision| &revision.transaction)
+                .cloned()
+                .reduce(|acc, transaction| acc.compose(transaction))
         }
-
-        // 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.
diff --git a/helix-term/src/ui/editor.rs b/helix-term/src/ui/editor.rs
index 44f89b77ed154..737125031e993 100644
--- a/helix-term/src/ui/editor.rs
+++ b/helix-term/src/ui/editor.rs
@@ -1424,7 +1424,7 @@ impl Component for EditorView {
                     // If the current document has been changed, apply the changes to all views.
                     // This ensures that selections in jumplists follow changes.
                     if doc.id() == original_doc_id
-                        && doc.get_current_revision() > original_doc_revision
+                        && doc.get_current_revision() != original_doc_revision
                     {
                         if let Some(transaction) =
                             doc.history.get_mut().changes_since(original_doc_revision)