readline: show completions only after 2nd TAB

Show `TAB` completion suggestions only after the user has pressed `TAB`
twice in a row, so that the full list of suggestions doesn’t present
a distraction. The first time a `TAB` key is pressed, only partial
longest-common-prefix completion is performed.

This moves the `readline` autocompletion a lot closer to what e.g.
`bash` does.

Fixes: https://github.com/nodejs/node/issues/7665
PR-URL: https://github.com/nodejs/node/pull/7754
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Trevor Norris <trev.norris@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: James M Snell <jasnell@gmail.com>

1 files changed, 9 insertions, 4 deletions

diff --git a/test/parallel/test-readline-undefined-columns.js b/test/parallel/test-readline-undefined-columns.js
index f3197ff59a..5f8a1c02d3 100644
--- a/test/parallel/test-readline-undefined-columns.js
+++ b/test/parallel/test-readline-undefined-columns.js
@@ -1,6 +1,6 @@
 'use strict';
 
-require('../common');
+const common = require('../common');
 const assert = require('assert');
 const PassThrough = require('stream').PassThrough;
 const readline = require('readline');
@@ -26,12 +26,17 @@ oStream.on('data', function(data) {
   output += data;
 });
 
-oStream.on('end', function() {
+oStream.on('end', common.mustCall(() => {
   const expect = 'process.stdout\r\n' +
                  'process.stdin\r\n' +
                  'process.stderr';
   assert(new RegExp(expect).test(output));
-});
+}));
+
+iStream.write('process.s\t');
+
+assert(/process.std\b/.test(output));  // Completion works.
+assert(!/stdout/.test(output));  // Completion doesn’t show all results yet.
 
-iStream.write('process.std\t');
+iStream.write('\t');
 oStream.end();