readline: establish y in cursorTo as optional

Parameter y in cursorTo() is optional and this is also verified by
tests but docs don't state this. Besides that if the newly added
parameter callback is used with no y, it's quite unhandy. This PR allows
to simply omit y.

PR-URL: #29128
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

doc/api/readline.md

@@ -487,7 +487,7 @@ function completer(linePartial, callback) {
 }
 ```
 
-## readline.cursorTo(stream, x, y[, callback])
+## readline.cursorTo(stream, x[, y][, callback])
 <!-- YAML
 added: v0.7.7
 changes:

doc/api/tty.md

@@ -145,7 +145,7 @@ added: v0.7.7
 A `number` specifying the number of columns the TTY currently has. This property
 is updated whenever the `'resize'` event is emitted.
 
-### writeStream.cursorTo(x, y[, callback])
+### writeStream.cursorTo(x[, y][, callback])
 <!-- YAML
 added: v0.7.7
 changes:

lib/readline.js

@@ -1193,6 +1193,11 @@ function cursorTo(stream, x, y, callback) {
   if (callback !== undefined && typeof callback !== 'function')
     throw new ERR_INVALID_CALLBACK(callback);
 
+  if (typeof y === 'function') {
+    callback = y;
+    y = undefined;
+  }
+
   if (stream == null || (typeof x !== 'number' && typeof y !== 'number')) {
     if (typeof callback === 'function')
       process.nextTick(callback);

test/parallel/test-readline-csi.js

@@ -133,6 +133,10 @@ writable.data = '';
 assert.strictEqual(readline.cursorTo(writable, 1, 'a'), true);
 assert.strictEqual(writable.data, '\x1b[2G');
 
+writable.data = '';
+assert.strictEqual(readline.cursorTo(writable, 1), true);
+assert.strictEqual(writable.data, '\x1b[2G');
+
 writable.data = '';
 assert.strictEqual(readline.cursorTo(writable, 1, 2), true);
 assert.strictEqual(writable.data, '\x1b[3;2H');
@@ -141,6 +145,10 @@ writable.data = '';
 assert.strictEqual(readline.cursorTo(writable, 1, 2, common.mustCall()), true);
 assert.strictEqual(writable.data, '\x1b[3;2H');
 
+writable.data = '';
+assert.strictEqual(readline.cursorTo(writable, 1, common.mustCall()), true);
+assert.strictEqual(writable.data, '\x1b[2G');
+
 // Verify that cursorTo() throws on invalid callback.
 assert.throws(() => {
   readline.cursorTo(writable, 1, 1, null);