Fix movePrimaryCursorIntoVisibleRange

src/commands/move.ts

@@ -314,7 +314,22 @@ export function movePrimaryCursorIntoVisibleRange(
   let newPrimaryActive: vscode.Position;
   if (primaryActive.isBefore(visibleRange.start)) {
     newPrimaryActive = visibleRange.start.with(undefined, 0);
-  } else if (primaryActive.isAfter(visibleRange.end)) {
+  } else if (
+    // This method is called in the `onDidChangeTextEditorVisibleRanges` callback,
+    // and it is called when the user edits the document maybe because the edit moves the cursor.
+    // When executing the `deleteLeft` command for example, the document is shortened by 1 character
+    // and the cursor is moved to 1 character left, which is correct. However, in this case,
+    // the `onDidChangeTextEditorVisibleRanges` is called before `textEditor.selection` is updated,
+    // so we can't compare `visibleRange` with `editor.selection.active` directly in this method,
+    // which causes the issue like https://github.com/whitphx/vscode-emacs-mcx/issues/2113.
+    // * To solve the issue https://github.com/whitphx/vscode-emacs-mcx/issues/2113, we compare the lines instead of the positions.
+    // * Also, we compare the primaryActive.line with visibleRange.end.line + 1
+    //   because, for example, when the cursor is at [lastLine, 0] and the `deleteLeft` command is executed,
+    //   `visibleRange.end.line` becomes `lastLine - 1` but the cursor position is still [lastLine, 0] when this method is called form the callback due to the problem stated above,
+    //   in which case the cursor is considered out of the visible range, which is incorrect.
+    primaryActive.line >
+    visibleRange.end.line + 1
+  ) {
     newPrimaryActive = visibleRange.end.with(undefined, 0);
   } else {
     return;

src/test/suite/keep-cursor-range.test.ts

@@ -1,15 +1,15 @@
 import assert from "assert";
 import * as vscode from "vscode";
 import { EmacsEmulator } from "../../emulator";
-import { cleanUpWorkspace, setupWorkspace, setEmptyCursors } from "./utils";
+import { cleanUpWorkspace, setupWorkspace, setEmptyCursors, assertCursorsEqual, delay } from "./utils";
 import { Configuration } from "../../configuration/configuration";
 
 suite("onDidChangeTextEditorVisibleRanges event listener with strictEmacsMove", () => {
   let activeTextEditor: vscode.TextEditor;
   let emulator: EmacsEmulator;
 
   setup(async () => {
-    const initialText = "x\n".repeat(1000);
+    const initialText = "xxxx\n".repeat(1000).slice(0, -1); // Delete the last newline
     activeTextEditor = await setupWorkspace(initialText);
     emulator = new EmacsEmulator(activeTextEditor); // `EmacsEmulator`'s constructor registers the event listener
   });
@@ -47,4 +47,22 @@ suite("onDidChangeTextEditorVisibleRanges event listener with strictEmacsMove",
 
     Configuration.reload();
   });
+
+  test("backspace works correctly keeping the cursor at the right position, when strictEmacsMove = true and the cursor is in the last line", async () => {
+    Configuration.instance.strictEmacsMove = true;
+
+    const lastLine = activeTextEditor.document.lineCount - 1;
+    const lastChar = activeTextEditor.document.lineAt(lastLine).text.length;
+
+    setEmptyCursors(activeTextEditor, [lastLine, lastChar]);
+    activeTextEditor.revealRange(new vscode.Range(lastLine, lastChar, lastLine, lastChar));
+
+    await vscode.commands.executeCommand("deleteLeft");
+
+    await delay(10); // Wait for the event listeners are called after the edit.
+
+    assertCursorsEqual(activeTextEditor, [lastLine, lastChar - 1]);
+
+    Configuration.reload();
+  });
 });