Made Scroll to Last Read Post optional. Close #1009

Fix a bug where it attempted to scroll to a hidden post without stub, effectively scrolling to the end of
the thread.

CHANGELOG.md

@@ -1,3 +1,4 @@
+- `Scroll to Last Read Post` is now optional, enabled by default.
 - The QR won't auto-hide when auto-hide is enabled and one of its input is focused. Doesn't work on Firefox.
 - Fix QR remembering the file spoiler state when it shouldn't.
 - Fix QR cooldown in Opera.

src/config.coffee

@@ -39,6 +39,7 @@ Config =
       'Unread Count':                 [true,  'Show the unread posts count in the tab title.']
       'Unread Tab Icon':              [true,  'Show a different favicon when there are unread posts.']
       'Unread Line':                  [true,  'Show a line to distinguish read posts from unread ones.']
+      'Scroll to Last Read Post':     [true,  'Scroll back to the last read post when reopening a thread.']
       'Thread Excerpt':               [true,  'Show an excerpt of the thread in the tab title.']
       'Thread Stats':                 [true,  'Display reply and image count.']
       'Thread Watcher':               [true,  'Bookmark threads.']

src/features.coffee

@@ -160,6 +160,7 @@ Header =
     (if hide then $.addClass else $.rmClass) Header.bar, 'autohide'
   hashScroll: ->
     return unless post = $.id @location.hash[1..]
+    return if (Get.postFromRoot post).isHidden
     Header.scrollToPost post
   scrollToPost: (post) ->
     {top} = post.getBoundingClientRect()
@@ -3709,18 +3710,22 @@ Unread =
       threadID: @ID
       defaultValue: 0
     Unread.addPosts posts
-    if (hash = location.hash.match /\d+/) and post = @posts[hash[0]]
-      Header.scrollToPost post.nodes.root
-    else if Unread.posts.length
-      # Scroll to before the first unread post.
-      $.x('preceding-sibling::div[contains(@class,"postContainer")][1]', Unread.posts[0].nodes.root).scrollIntoView false
-    else if posts.length
-      # Scroll to the last read post.
-      Header.scrollToPost posts[posts.length - 1].nodes.root
     $.on d, 'ThreadUpdate',            Unread.onUpdate
     $.on d, 'scroll visibilitychange', Unread.read
     $.on d, 'visibilitychange',        Unread.setLine if Conf['Unread Line']
 
+    return unless Conf['Scroll to Last Read Post']
+    # Let the header's onload callback handle it.
+    return if (hash = location.hash.match /\d+/) and hash[0] of @posts
+    if Unread.posts.length
+      # Scroll to before the first unread post.
+      while root = $.x 'preceding-sibling::div[contains(@class,"postContainer")][1]', Unread.posts[0].nodes.root
+        break unless (Get.postFromRoot root).isHidden
+      root.scrollIntoView false
+    else if posts.length
+      # Scroll to the last read post.
+      Header.scrollToPost posts[posts.length - 1].nodes.root
+
   sync: ->
     lastReadPost = Unread.db.get
       boardID: Unread.thread.board.ID