repl tab completion: insert common prefix of multiple completions

lib/readline.js

@@ -160,7 +160,6 @@ Interface.prototype._tabComplete = function () {
       self._insertString(completions[0].slice(completeOn.length));
       self._refreshLine();
     } else {
-      //TODO: If there is a common prefix to all matches (e.g. Python `sys.exi<Tab>`) then apply that portion
       self.output.write("\r\n");
       var width = completions.reduce(function(a, b) {
         return a.length > b.length ? a : b;
@@ -191,8 +190,8 @@ Interface.prototype._tabComplete = function () {
         self.output.write('\r\n');
       }
 
-      var group = [], c;
+      var group = [], c, i;
-      for (var i = 0; i < completions.length; i++) {
+      for (i = 0; i < completions.length; i++) {
         c = completions[i];
         if (c === "") {
           handleGroup(group);
@@ -202,11 +201,35 @@ Interface.prototype._tabComplete = function () {
         }
       }
       handleGroup(group);
+
+      // If there is a common prefix to all matches, then apply that
+      // portion.
+      var prefix = commonPrefix(
+        completions.filter(function(e) { if (e) return e }));
+      if (prefix.length > completeOn.length) {
+        self._insertString(prefix.slice(completeOn.length));
+      }
+
       self._refreshLine();
     }
   }
 };
 
+function commonPrefix(strings) {
+  if (!strings || strings.length == 0) {
+    return "";
+  }
+  var sorted = strings.slice().sort();
+  var min = sorted[0];
+  var max = sorted[sorted.length - 1];
+  for (var i = 0; i < min.length; i++) {
+    if (min[i] != max[i]) {
+      return min.slice(0, i);
+    }
+  }
+  return min;
+}
+
 Interface.prototype._historyNext = function () {
   if (this.historyIndex > 0) {
     this.historyIndex--;