Add back keyboard support within allowClear

This adds back keyboard support, so you can now clear a selected
item using either the backspace or delete key.  This only work when
the container is closed, to prevent issues with the selection being
clear while a user is searching.

This was a regression in accessibility from 3.x.

This closes https://github.com/select2/select2/issues/3224.

dist/js/select2.full.js

@@ -1638,8 +1638,9 @@ S2.define('select2/selection/placeholder',[
 });
 
 S2.define('select2/selection/allowClear',[
-  'jquery'
-], function ($) {
+  'jquery',
+  '../keys'
+], function ($, KEYS) {
   function AllowClear () { }
 
   AllowClear.prototype.bind = function (decorated, container, $container) {
@@ -1647,8 +1648,8 @@ S2.define('select2/selection/allowClear',[
 
     decorated.call(this, container, $container);
 
-    if (self.placeholder == null) {
-      if (self.options.get('debug') && window.console && console.error) {
+    if (this.placeholder == null) {
+      if (this.options.get('debug') && window.console && console.error) {
         console.error(
           'Select2: The `allowClear` option should be used in combination ' +
           'with the `placeholder` option.'
@@ -1658,34 +1659,61 @@ S2.define('select2/selection/allowClear',[
 
     this.$selection.on('mousedown', '.select2-selection__clear',
       function (evt) {
-        // Ignore the event if it is disabled
-        if (self.options.get('disabled')) {
-          return;
-        }
+        self._handleClear(evt);
+    });
 
-        evt.stopPropagation();
+    container.on('keypress', function (evt) {
+      self._handleKeyboardClear(evt, container);
+    });
+  };
 
-        var data = $(this).data('data');
+  AllowClear.prototype._handleClear = function (_, evt) {
+    console.log(arguments);
 
-        for (var d = 0; d < data.length; d++) {
-          var unselectData = {
-            data: data[d]
-          };
+    // Ignore the event if it is disabled
+    if (this.options.get('disabled')) {
+      return;
+    }
 
-          // Trigger the `unselect` event, so people can prevent it from being
-          // cleared.
-          self.trigger('unselect', unselectData);
+    var $clear = this.$selection.find('.select2-selection__clear');
 
-          // If the event was prevented, don't clear it out.
-          if (unselectData.prevented) {
-            return;
-          }
-        }
+    // Ignore the event if nothing has been selected
+    if ($clear.length === 0) {
+      return;
+    }
 
-        self.$element.val(self.placeholder.id).trigger('change');
+    evt.stopPropagation();
 
-        self.trigger('toggle');
-    });
+    var data = $clear.data('data');
+
+    for (var d = 0; d < data.length; d++) {
+      var unselectData = {
+        data: data[d]
+      };
+
+      // Trigger the `unselect` event, so people can prevent it from being
+      // cleared.
+      this.trigger('unselect', unselectData);
+
+      // If the event was prevented, don't clear it out.
+      if (unselectData.prevented) {
+        return;
+      }
+    }
+
+    this.$element.val(this.placeholder.id).trigger('change');
+
+    this.trigger('toggle');
+  };
+
+  AllowClear.prototype._handleKeyboardClear = function (_, evt, container) {
+    if (container.isOpen()) {
+      return;
+    }
+
+    if (evt.which == KEYS.DELETE || evt.which == KEYS.BACKSPACE) {
+      this._handleClear(evt);
+    }
   };
 
   AllowClear.prototype.update = function (decorated, data) {

dist/js/select2.js

@@ -1638,8 +1638,9 @@ S2.define('select2/selection/placeholder',[
 });
 
 S2.define('select2/selection/allowClear',[
-  'jquery'
-], function ($) {
+  'jquery',
+  '../keys'
+], function ($, KEYS) {
   function AllowClear () { }
 
   AllowClear.prototype.bind = function (decorated, container, $container) {
@@ -1647,8 +1648,8 @@ S2.define('select2/selection/allowClear',[
 
     decorated.call(this, container, $container);
 
-    if (self.placeholder == null) {
-      if (self.options.get('debug') && window.console && console.error) {
+    if (this.placeholder == null) {
+      if (this.options.get('debug') && window.console && console.error) {
         console.error(
           'Select2: The `allowClear` option should be used in combination ' +
           'with the `placeholder` option.'
@@ -1658,34 +1659,61 @@ S2.define('select2/selection/allowClear',[
 
     this.$selection.on('mousedown', '.select2-selection__clear',
       function (evt) {
-        // Ignore the event if it is disabled
-        if (self.options.get('disabled')) {
-          return;
-        }
+        self._handleClear(evt);
+    });
 
-        evt.stopPropagation();
+    container.on('keypress', function (evt) {
+      self._handleKeyboardClear(evt, container);
+    });
+  };
 
-        var data = $(this).data('data');
+  AllowClear.prototype._handleClear = function (_, evt) {
+    console.log(arguments);
 
-        for (var d = 0; d < data.length; d++) {
-          var unselectData = {
-            data: data[d]
-          };
+    // Ignore the event if it is disabled
+    if (this.options.get('disabled')) {
+      return;
+    }
 
-          // Trigger the `unselect` event, so people can prevent it from being
-          // cleared.
-          self.trigger('unselect', unselectData);
+    var $clear = this.$selection.find('.select2-selection__clear');
 
-          // If the event was prevented, don't clear it out.
-          if (unselectData.prevented) {
-            return;
-          }
-        }
+    // Ignore the event if nothing has been selected
+    if ($clear.length === 0) {
+      return;
+    }
 
-        self.$element.val(self.placeholder.id).trigger('change');
+    evt.stopPropagation();
 
-        self.trigger('toggle');
-    });
+    var data = $clear.data('data');
+
+    for (var d = 0; d < data.length; d++) {
+      var unselectData = {
+        data: data[d]
+      };
+
+      // Trigger the `unselect` event, so people can prevent it from being
+      // cleared.
+      this.trigger('unselect', unselectData);
+
+      // If the event was prevented, don't clear it out.
+      if (unselectData.prevented) {
+        return;
+      }
+    }
+
+    this.$element.val(this.placeholder.id).trigger('change');
+
+    this.trigger('toggle');
+  };
+
+  AllowClear.prototype._handleKeyboardClear = function (_, evt, container) {
+    if (container.isOpen()) {
+      return;
+    }
+
+    if (evt.which == KEYS.DELETE || evt.which == KEYS.BACKSPACE) {
+      this._handleClear(evt);
+    }
   };
 
   AllowClear.prototype.update = function (decorated, data) {

src/js/select2/selection/allowClear.js

@@ -1,6 +1,7 @@
 define([
-  'jquery'
-], function ($) {
+  'jquery',
+  '../keys'
+], function ($, KEYS) {
   function AllowClear () { }
 
   AllowClear.prototype.bind = function (decorated, container, $container) {
@@ -8,8 +9,8 @@ define([
 
     decorated.call(this, container, $container);
 
-    if (self.placeholder == null) {
-      if (self.options.get('debug') && window.console && console.error) {
+    if (this.placeholder == null) {
+      if (this.options.get('debug') && window.console && console.error) {
         console.error(
           'Select2: The `allowClear` option should be used in combination ' +
           'with the `placeholder` option.'
@@ -19,34 +20,59 @@ define([
 
     this.$selection.on('mousedown', '.select2-selection__clear',
       function (evt) {
-        // Ignore the event if it is disabled
-        if (self.options.get('disabled')) {
-          return;
-        }
+        self._handleClear(evt);
+    });
+
+    container.on('keypress', function (evt) {
+      self._handleKeyboardClear(evt, container);
+    });
+  };
+
+  AllowClear.prototype._handleClear = function (_, evt) {
+    // Ignore the event if it is disabled
+    if (this.options.get('disabled')) {
+      return;
+    }
 
-        evt.stopPropagation();
+    var $clear = this.$selection.find('.select2-selection__clear');
 
-        var data = $(this).data('data');
+    // Ignore the event if nothing has been selected
+    if ($clear.length === 0) {
+      return;
+    }
 
-        for (var d = 0; d < data.length; d++) {
-          var unselectData = {
-            data: data[d]
-          };
+    evt.stopPropagation();
 
-          // Trigger the `unselect` event, so people can prevent it from being
-          // cleared.
-          self.trigger('unselect', unselectData);
+    var data = $clear.data('data');
 
-          // If the event was prevented, don't clear it out.
-          if (unselectData.prevented) {
-            return;
-          }
-        }
+    for (var d = 0; d < data.length; d++) {
+      var unselectData = {
+        data: data[d]
+      };
 
-        self.$element.val(self.placeholder.id).trigger('change');
+      // Trigger the `unselect` event, so people can prevent it from being
+      // cleared.
+      this.trigger('unselect', unselectData);
 
-        self.trigger('toggle');
-    });
+      // If the event was prevented, don't clear it out.
+      if (unselectData.prevented) {
+        return;
+      }
+    }
+
+    this.$element.val(this.placeholder.id).trigger('change');
+
+    this.trigger('toggle');
+  };
+
+  AllowClear.prototype._handleKeyboardClear = function (_, evt, container) {
+    if (container.isOpen()) {
+      return;
+    }
+
+    if (evt.which == KEYS.DELETE || evt.which == KEYS.BACKSPACE) {
+      this._handleClear(evt);
+    }
   };
 
   AllowClear.prototype.update = function (decorated, data) {