fix #https://github.com/microsoft/vscode/issues/123000

src/common/buffer/BufferRange.test.ts

@@ -0,0 +1,32 @@
+/**
+ * Copyright (c) 2021 The xterm.js authors. All rights reserved.
+ * @license MIT
+ */
+
+import { assert } from 'chai';
+import { getRangeLength } from 'common/buffer/BufferRange';
+import { IBufferRange } from 'xterm';
+
+describe.only('BufferRange', () => {
+  describe('getRangeLength', () => {
+    it('should get range for single line', () => {
+      assert.equal(getRangeLength(createRange(1, 1, 4, 1), 0), 3);
+    });
+    it('should throw for invalid range', () => {
+      assert.throws(() => getRangeLength(createRange(1, 3, 1, 1), 0));
+    });
+    it('should get range multiple lines', () => {
+      assert.equal(getRangeLength(createRange(1, 1, 4, 5), 5), 23);
+    });
+    it('should get range for end line right after start line', () => {
+      assert.equal(getRangeLength(createRange(1, 1, 7, 2), 5), 11);
+    });
+  });
+});
+
+function createRange(x1: number, y1: number, x2: number, y2: number): IBufferRange {
+  return {
+    start: { x: x1, y: y1 },
+    end: { x: x2, y: y2 }
+  };
+}

src/common/buffer/BufferRange.ts

@@ -0,0 +1,16 @@
+/**
+ * Copyright (c) 2021 The xterm.js authors. All rights reserved.
+ * @license MIT
+ */
+
+import { IBufferRange } from 'xterm';
+
+export function getRangeLength(range: IBufferRange, cols: number): number {
+  if (range.start.y === range.end.y) {
+    return range.end.x - range.start.x;
+  }
+  if (range.start.y > range.end.y) {
+    throw new Error(`Buffer range end (${range.end.x}, ${range.end.y}) cannot be before start (${range.start.x}, ${range.start.y})`);
+  }
+  return cols * (range.end.y - range.start.y - 1) + cols - range.start.x + range.end.x;
+}