Expand the issuable sidebar when coming back from the Changes tab

Unless the user explicitly requested the collapsed sidebar.

app/assets/javascripts/merge_request_tabs.js.coffee

@@ -3,6 +3,8 @@
 # Handles persisting and restoring the current tab selection and lazily-loading
 # content on the MergeRequests#show page.
 #
+#= require jquery.cookie
+#
 # ### Example Markup
 #
 #   <ul class="nav-links merge-request-tabs">
@@ -68,11 +70,15 @@ class @MergeRequestTabs
 
     if action == 'commits'
       @loadCommits($target.attr('href'))
+      @expandView()
     else if action == 'diffs'
       @loadDiff($target.attr('href'))
       @shrinkView()
     else if action == 'builds'
       @loadBuilds($target.attr('href'))
+      @expandView()
+    else
+      @expandView()
 
     @setCurrentAction(action)
 
@@ -189,11 +195,24 @@ class @MergeRequestTabs
     $('.container-fluid').removeClass('container-limited')
 
   shrinkView: ->
-    $gutterIcon = $('.js-sidebar-toggle i')
+    $gutterIcon = $('.js-sidebar-toggle i:visible')
 
     # Wait until listeners are set
     setTimeout( ->
-      # Only when sidebar is collapsed
+      # Only when sidebar is expanded
       if $gutterIcon.is('.fa-angle-double-right')
-        $gutterIcon.closest('a').trigger('click',[true])
+        $gutterIcon.closest('a').trigger('click', [true])
+    , 0)
+
+  # Expand the issuable sidebar unless the user explicitly collapsed it
+  expandView: ->
+    return if $.cookie('collapsed_gutter') == 'true'
+
+    $gutterIcon = $('.js-sidebar-toggle i:visible')
+
+    # Wait until listeners are set
+    setTimeout( ->
+      # Only when sidebar is collapsed
+      if $gutterIcon.is('.fa-angle-double-left')
+        $gutterIcon.closest('a').trigger('click', [true])
     , 0)