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, 15 insertions, 13 deletions

diff --git a/lib/readline.js b/lib/readline.js
index 402923e925..9d34bb740d 100644
--- a/lib/readline.js
+++ b/lib/readline.js
@@ -41,6 +41,7 @@ function Interface(input, output, completer, terminal) {
 
   this._sawReturn = false;
   this.isCompletionEnabled = true;
+  this._previousKey = null;
 
   EventEmitter.call(this);
   var historySize;
@@ -391,7 +392,7 @@ Interface.prototype._insertString = function(c) {
   }
 };
 
-Interface.prototype._tabComplete = function() {
+Interface.prototype._tabComplete = function(lastKeypressWasTab) {
   var self = this;
 
   self.pause();
@@ -407,9 +408,7 @@ Interface.prototype._tabComplete = function() {
     const completeOn = rv[1];  // the text that was completed
     if (completions && completions.length) {
       // Apply/show completions.
-      if (completions.length === 1) {
-        self._insertString(completions[0].slice(completeOn.length));
-      } else {
+      if (lastKeypressWasTab) {
         self._writeToOutput('\r\n');
         var width = completions.reduce(function(a, b) {
           return a.length > b.length ? a : b;
@@ -429,16 +428,15 @@ Interface.prototype._tabComplete = function() {
           }
         }
         handleGroup(self, group, width, maxColumns);
+      }
 
-        // If there is a common prefix to all matches, then apply that
-        // portion.
-        var f = completions.filter(function(e) { if (e) return e; });
-        var prefix = commonPrefix(f);
-        if (prefix.length > completeOn.length) {
-          self._insertString(prefix.slice(completeOn.length));
-        }
-
+      // If there is a common prefix to all matches, then apply that portion.
+      const f = completions.filter(function(e) { if (e) return e; });
+      const prefix = commonPrefix(f);
+      if (prefix.length > completeOn.length) {
+        self._insertString(prefix.slice(completeOn.length));
       }
+
       self._refreshLine();
     }
   });
@@ -474,6 +472,7 @@ function commonPrefix(strings) {
   if (!strings || strings.length == 0) {
     return '';
   }
+  if (strings.length === 1) return strings[0];
   var sorted = strings.slice().sort();
   var min = sorted[0];
   var max = sorted[sorted.length - 1];
@@ -688,7 +687,9 @@ Interface.prototype._moveCursor = function(dx) {
 
 // handle a write from the tty
 Interface.prototype._ttyWrite = function(s, key) {
+  const previousKey = this._previousKey;
   key = key || {};
+  this._previousKey = key;
 
   // Ignore escape key - Fixes #2876
   if (key.name == 'escape') return;
@@ -892,7 +893,8 @@ Interface.prototype._ttyWrite = function(s, key) {
       case 'tab':
         // If tab completion enabled, do that...
         if (typeof this.completer === 'function' && this.isCompletionEnabled) {
-          this._tabComplete();
+          const lastKeypressWasTab = previousKey && previousKey.name === 'tab';
+          this._tabComplete(lastKeypressWasTab);
           break;
         }
         // falls through