[IMP] mail: load more messages: scrolling

- In the chat, when loading more messages, automatically scroll to the previous
oldest message instead of staying at the top;
- In the chat, don't use the event 'scrollTop < 50' to load more messages as
it won't work on mobile (all the webclient is scrolling, so the client action's
scrollTop will always be 0);
- Generalize the way to load more messages between chat and chatter by moving
the logic to the MailThreadMixin and creating a common template;
- Improve the style of this 'load more messages' button

3 files changed, 8 insertions, 4 deletions

diff --git a/addons/mail/static/src/xml/mail_chat_backend.xml b/addons/mail/static/src/xml/mail_chat_backend.xml
index acbc4b39a33..253cd1e95aa 100644
--- a/addons/mail/static/src/xml/mail_chat_backend.xml
+++ b/addons/mail/static/src/xml/mail_chat_backend.xml
@@ -116,6 +116,7 @@
     -->
     <t t-name="mail.chat.ChatMailThread.content">
         <t t-if="widget.get('messages').length">
+            <t t-call="mail.Thread.load_more"/>
             <t t-call="mail.Thread.messages"/>
         </t>
         <t t-if="!widget.get('messages').length">
diff --git a/addons/mail/static/src/xml/mail_chatter.xml b/addons/mail/static/src/xml/mail_chatter.xml
index 813a07946e5..47f17fa4957 100644
--- a/addons/mail/static/src/xml/mail_chatter.xml
+++ b/addons/mail/static/src/xml/mail_chatter.xml
@@ -67,16 +67,13 @@
             <div class="o_mail_chatter_compose_message"/>
             <!-- Message list -->
             <div class="o_mail_chatter_messages"/>
-
-            <div t-if="widget.options.display_show_more_message" class="o_mail_chatter_show_more_message text-muted">
-                ----------- Show more messages -----------
-            </div>
         </div>
     </t>
 
     <t t-name="mail.chatter.ChatterMailThread.messages">
         <t t-if="widget.get('messages').length">
             <t t-call="mail.Thread.messages"/>
+            <t t-call="mail.Thread.load_more"/>
         </t>
         <t t-if="!widget.get('messages').length">
             No Messages.
diff --git a/addons/mail/static/src/xml/mail_thread.xml b/addons/mail/static/src/xml/mail_thread.xml
index f4aad0754b1..e650dd323fc 100644
--- a/addons/mail/static/src/xml/mail_thread.xml
+++ b/addons/mail/static/src/xml/mail_thread.xml
@@ -158,6 +158,12 @@
         </t>
     </t>
 
+    <t t-name="mail.Thread.load_more">
+        <div t-if="!widget.all_messages_loaded" class="o_mail_thread_show_more">
+            <button class="btn btn-sm btn-link">-------- Show more messages --------</button>
+        </div>
+    </t>
+
     <t t-name="mail.Thread.tracking_message">
         <div>
             <ul class="o_mail_thread_message_tracking">