Added back select2("data")

In the past, `select2("data")` allowed you to retrieve the currently
selected data objects.  Read-only support has been added back for
this, which maps to the `current` method of the data adapter.  This
will only work for data adapters which allow for the synchronous
retrieval of the current data, which is the case for all of the
default data adapters.

You could also previously overwrite the currently selected data
objects by passing in an argument to `select2("data")`.  As this
dealt directly with the internals, and required a considerable
amount of work to synchronize it, it has been removed.  A warning
will now be triggered if the method is called with additional
elements, and the `val` method should be used instead.

This closes https://github.com/select2/select2/issues/2938.

dist/js/select2.amd.full.js

@@ -4531,6 +4531,23 @@ define('select2/core',[
     this.$element.prop('disabled', disabled);
   };
 
+  Select2.prototype.data = function () {
+    if (arguments.length > 0 && console && console.warn) {
+      console.warn(
+        'Select2: Data can no longer be set using `select2("data")`. You ' +
+        'should consider setting the value instead using `$element.val()`.'
+      );
+    }
+
+    var data = [];
+
+    this.dataAdpater.current(function (currentData) {
+      data = currentData;
+    });
+
+    return data;
+  };
+
   Select2.prototype.val = function (args) {
     if (console && console.warn) {
       console.warn(

dist/js/select2.amd.js

@@ -4531,6 +4531,23 @@ define('select2/core',[
     this.$element.prop('disabled', disabled);
   };
 
+  Select2.prototype.data = function () {
+    if (arguments.length > 0 && console && console.warn) {
+      console.warn(
+        'Select2: Data can no longer be set using `select2("data")`. You ' +
+        'should consider setting the value instead using `$element.val()`.'
+      );
+    }
+
+    var data = [];
+
+    this.dataAdpater.current(function (currentData) {
+      data = currentData;
+    });
+
+    return data;
+  };
+
   Select2.prototype.val = function (args) {
     if (console && console.warn) {
       console.warn(

dist/js/select2.full.js

@@ -4969,6 +4969,23 @@ define('select2/core',[
     this.$element.prop('disabled', disabled);
   };
 
+  Select2.prototype.data = function () {
+    if (arguments.length > 0 && console && console.warn) {
+      console.warn(
+        'Select2: Data can no longer be set using `select2("data")`. You ' +
+        'should consider setting the value instead using `$element.val()`.'
+      );
+    }
+
+    var data = [];
+
+    this.dataAdpater.current(function (currentData) {
+      data = currentData;
+    });
+
+    return data;
+  };
+
   Select2.prototype.val = function (args) {
     if (console && console.warn) {
       console.warn(

dist/js/select2.js

@@ -4969,6 +4969,23 @@ define('select2/core',[
     this.$element.prop('disabled', disabled);
   };
 
+  Select2.prototype.data = function () {
+    if (arguments.length > 0 && console && console.warn) {
+      console.warn(
+        'Select2: Data can no longer be set using `select2("data")`. You ' +
+        'should consider setting the value instead using `$element.val()`.'
+      );
+    }
+
+    var data = [];
+
+    this.dataAdpater.current(function (currentData) {
+      data = currentData;
+    });
+
+    return data;
+  };
+
   Select2.prototype.val = function (args) {
     if (console && console.warn) {
       console.warn(

src/js/select2/core.js

@@ -408,6 +408,23 @@ define([
     this.$element.prop('disabled', disabled);
   };
 
+  Select2.prototype.data = function () {
+    if (arguments.length > 0 && console && console.warn) {
+      console.warn(
+        'Select2: Data can no longer be set using `select2("data")`. You ' +
+        'should consider setting the value instead using `$element.val()`.'
+      );
+    }
+
+    var data = [];
+
+    this.dataAdpater.current(function (currentData) {
+      data = currentData;
+    });
+
+    return data;
+  };
+
   Select2.prototype.val = function (args) {
     if (console && console.warn) {
       console.warn(