ARIA support for collapse

Added handling of aria-expanded=true/false to collapse.js, updated
documentation to include advice on making expand/collapse controls
accessible, updated examples and javascript documentation to use
aria-expanded and aria-controls (when targetting single collapsible
element, using ID rather than class selector)

Closes #14147.
Closes #14153.

js/collapse.js

@@ -56,6 +56,7 @@
     this.$element
       .removeClass('collapse')
       .addClass('collapsing')[dimension](0)
+      .attr('aria-expanded', true)
 
     this.transitioning = 1
 
@@ -91,6 +92,7 @@
     this.$element
       .addClass('collapsing')
       .removeClass('collapse in')
+      .attr('aria-expanded', false)
 
     this.transitioning = 1
 
@@ -161,8 +163,9 @@
     var $parent = parent && $(parent)
 
     if (!data || !data.transitioning) {
-      if ($parent) $parent.find('[data-toggle="collapse"][data-parent="' + parent + '"]').not($this).addClass('collapsed')
-      $this.toggleClass('collapsed', $target.hasClass('in'))
+      if ($parent) $parent.find('[data-toggle="collapse"][data-parent="' + parent + '"]').not($this).addClass('collapsed').attr('aria-expanded', false)
+      var isCollapsed = $target.hasClass('in')
+      $this.toggleClass('collapsed', isCollapsed).attr('aria-expanded', !isCollapsed)
     }
 
     Plugin.call($target, option)

js/tests/unit/collapse.js

@@ -75,7 +75,7 @@ $(function () {
   test('should remove "collapsed" class from target when collapse is shown', function () {
     stop()
 
-    var $target = $('<a data-toggle="collapse" href="#test1"/>').appendTo('#qunit-fixture')
+    var $target = $('<a data-toggle="collapse" class="collapsed" href="#test1"/>').appendTo('#qunit-fixture')
 
     $('<div id="test1"/>')
       .appendTo('#qunit-fixture')
@@ -200,4 +200,67 @@ $(function () {
     $target3.click()
   })
 
-})
+  test('should set aria-expanded="true" on target when collapse is shown', function () {
+    stop()
+
+    var $target = $('<a data-toggle="collapse" class="collapsed" href="#test1" aria-expanded="false"/>').appendTo('#qunit-fixture')
+
+    $('<div id="test1"/>')
+      .appendTo('#qunit-fixture')
+      .on('show.bs.collapse', function () {
+        equal($target.attr('aria-expanded'), 'true', 'aria-expanded on target is "true"')
+        start()
+      })
+
+    $target.click()
+  })
+
+  test('should set aria-expanded="false" on target when collapse is hidden', function () {
+    stop()
+
+    var $target = $('<a data-toggle="collapse" href="#test1" aria-expanded="true"/>').appendTo('#qunit-fixture')
+
+    $('<div id="test1" class="in"/>')
+      .appendTo('#qunit-fixture')
+      .on('hide.bs.collapse', function () {
+        equal($target.attr('aria-expanded'), 'false', 'aria-expanded on target is "false"')
+        start()
+      })
+
+    $target.click()
+  })
+
+  test('should change aria-expanded from active accordion target to "false" and set the newly active one to "true"', function () {
+    stop()
+
+    var accordionHTML = '<div id="accordion">'
+        + '<div class="accordion-group"/>'
+        + '<div class="accordion-group"/>'
+        + '<div class="accordion-group"/>'
+        + '</div>'
+    var $groups = $(accordionHTML).appendTo('#qunit-fixture').find('.accordion-group')
+
+    var $target1 = $('<a data-toggle="collapse" href="#body1" data-parent="#accordion"/>').appendTo($groups.eq(0))
+
+    $('<div id="body1" aria-expanded="true" class="in"/>').appendTo($groups.eq(0))
+
+    var $target2 = $('<a class="collapsed" data-toggle="collapse" href="#body2" data-parent="#accordion"/>').appendTo($groups.eq(1))
+
+    $('<div id="body2" aria-expanded="false"/>').appendTo($groups.eq(1))
+
+    var $target3 = $('<a class="collapsed" data-toggle="collapse" href="#body3" data-parent="#accordion"/>').appendTo($groups.eq(2))
+
+    $('<div id="body3" aria-expanded="false"/>')
+      .appendTo($groups.eq(2))
+      .on('show.bs.collapse', function () {
+        equal($target1.attr('aria-expanded'), 'false', 'inactive target 1 has aria-expanded="false"')
+        equal($target2.attr('aria-expanded'), 'false', 'inactive target 2 has aria-expanded="false"')
+        equal($target3.attr('aria-expanded'), 'true', 'active target 3 has aria-expanded="false"')
+
+        start()
+      })
+
+    $target3.click()
+  })
+
+})