[master] d109b419c doc: Mention remaining VCL changes

[Dridi Boukelmoune]

commit d109b419cda9dbf7fc6c12eb50d80d5d2452e9aa
Author: Dridi Boukelmoune <dridi.boukelmoune at gmail.com>
Date:   Fri Sep 11 16:09:15 2020 +0200

    doc: Mention remaining VCL changes
    
    Leaving out any change that is solely a bug fix on purpose.

diff --git a/doc/sphinx/whats-new/changes-trunk.rst b/doc/sphinx/whats-new/changes-trunk.rst
index da9782274..8a0e637f2 100644
--- a/doc/sphinx/whats-new/changes-trunk.rst
+++ b/doc/sphinx/whats-new/changes-trunk.rst
@@ -38,6 +38,21 @@ Changes to VCL
 VCL variables
 ~~~~~~~~~~~~~
 
+A new ``obj.can_esi`` variable has been added to identify whether the response
+can be ESI processed.
+
+Once ``resp.filters`` is explicitly set, trying to set a ``resp.do_*`` field
+results in a VCL failure. The same rule applies to ``beresp.filters`` and
+``beresp.do_*`` fields.
+
+The ``BACKEND`` VCL type now has a ``.resolve()`` method to find the effective
+backend directly from VCL. When a director is selected, the resolution would
+otherwise be delayed until after returning from ``vcl_backend_fetch`` or
+``vcl_pipe``::
+
+    # eager backend selection
+    set bereq.backend = bereq.backend.resolve();
+
 It is now possible to manually set a ``Connection: close`` header in
 ``beresp`` to signal that the backend connection shouldn't be recycled.
 This might help dealing with backends that would under certain circumstances
@@ -57,11 +72,16 @@ header::
         }
     }
 
-**XXX new, deprecated or removed variables, or changed semantics**
-
 Other changes to VCL
 ~~~~~~~~~~~~~~~~~~~~
 
+A failure in ``vcl_recv`` could resume execution in ``vcl_hash`` before
+effectively ending the transaction, this has been corrected. A failure in
+``vcl_recv`` is now definitive.
+
+There is a new syntax for ``BLOB`` literals: ``:<base64>:``. This syntax is
+also used to automatically cast a blob into a string.
+
 VMODs
 =====