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>

2 files changed, 49 insertions, 3 deletions

diff --git a/helix-term/src/ui/editor.rs b/helix-term/src/ui/editor.rs
index 6c8ee2d9..44f89b77 100644
--- a/helix-term/src/ui/editor.rs
+++ b/helix-term/src/ui/editor.rs
@@ -1337,7 +1337,9 @@ impl Component for EditorView {
                 cx.editor.status_msg = None;
 
                 let mode = cx.editor.mode();
-                let (view, _) = current!(cx.editor);
+                let (view, doc) = current!(cx.editor);
+                let original_doc_id = doc.id();
+                let original_doc_revision = doc.get_current_revision();
                 let focus = view.id;
 
                 if let Some(on_next_key) = self.on_next_key.take() {
@@ -1413,13 +1415,31 @@ impl Component for EditorView {
                     let view = view_mut!(cx.editor, focus);
                     let doc = doc_mut!(cx.editor, &view.doc);
 
-                    view.ensure_cursor_in_view(doc, config.scrolloff);
-
                     // Store a history state if not in insert mode. This also takes care of
                     // committing changes when leaving insert mode.
                     if mode != Mode::Insert {
                         doc.append_changes_to_history(view.id);
                     }
+
+                    // 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
+                    {
+                        if let Some(transaction) =
+                            doc.history.get_mut().changes_since(original_doc_revision)
+                        {
+                            let doc = doc!(cx.editor, &original_doc_id);
+                            for (view, _focused) in cx.editor.tree.views_mut() {
+                                view.apply(&transaction, doc);
+                            }
+                        }
+                    }
+
+                    let view = view_mut!(cx.editor, focus);
+                    let doc = doc_mut!(cx.editor, &view.doc);
+
+                    view.ensure_cursor_in_view(doc, config.scrolloff);
                 }
 
                 EventResult::Consumed(callback)
diff --git a/helix-term/tests/test/splits.rs b/helix-term/tests/test/splits.rs
index 5807413a..a51de365 100644
--- a/helix-term/tests/test/splits.rs
+++ b/helix-term/tests/test/splits.rs
@@ -127,3 +127,29 @@ async fn test_split_write_quit_same_file() -> anyhow::Result<()> {
 
     Ok(())
 }
+
+#[tokio::test(flavor = "multi_thread")]
+async fn test_changes_in_splits_apply_to_all_views() -> anyhow::Result<()> {
+    // See <https://github.com/helix-editor/helix/issues/4732>.
+    // Transactions must be applied to any view that has the changed document open.
+    // This sequence would panic since the jumplist entry would be modified in one
+    // window but not the other. Attempting to update the changelist in the other
+    // window would cause a panic since it would point outside of the document.
+
+    // The key sequence here:
+    // * <C-w>v       Create a vertical split of the current buffer.
+    //                Both views look at the same doc.
+    // * [<space>     Add a line ending to the beginning of the document.
+    //                The cursor is now at line 2 in window 2.
+    // * <C-s>        Save that selection to the jumplist in window 2.
+    // * <C-w>w       Switch to window 1.
+    // * kd           Delete line 1 in window 1.
+    // * <C-w>q       Close window 1, focusing window 2.
+    // * d            Delete line 1 in window 2.
+    //
+    // This panicked in the past because the jumplist entry on line 2 of window 2
+    // was not updated and after the `kd` step, pointed outside of the document.
+    test(("#[|]#", "<C-w>v[<space><C-s><C-w>wkd<C-w>qd", "#[|]#")).await?;
+
+    Ok(())
+}