repl: fix tab completion for defined commands

PR-URL: https://github.com/nodejs/node/pull/7364
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>

lib/repl.js

@@ -659,11 +659,11 @@ REPLServer.prototype.complete = function(line, callback) {
 
   // REPL commands (e.g. ".break").
   var match = null;
-  match = line.match(/^\s*(\.\w*)$/);
+  match = line.match(/^\s*\.(\w*)$/);
   if (match) {
     completionGroups.push(Object.keys(this.commands));
     completeOn = match[1];
-    if (match[1].length > 1) {
+    if (match[1].length) {
       filter = match[1];
     }
 

test/parallel/test-repl-tab-complete.js

@@ -306,3 +306,10 @@ putIn.run(['var obj = {1:"a","1a":"b",a:"b"};']);
 testMe.complete('obj.', common.mustCall(function(error, data) {
   assert.deepEqual(data, obj_elements);
 }));
+
+// tab completion for defined commands
+putIn.run(['.clear']);
+
+testMe.complete('.b', common.mustCall((error, data) => {
+  assert.deepStrictEqual(data, [['break'], 'b']);
+}));