[IMP] qweb: Allow to propagate value to variables outside the loop.

If the variable was existing outside the context of the ``foreach``,
the value is copied at the end of the foreach into the global context.

Fix #4461 - Q74531 - Q71486 - Q71675

addons/web/static/lib/qweb/qweb2.js

@@ -187,6 +187,10 @@ var QWeb2 = {
                         }
                       }
                 }
+
+                _.each(Object.keys(old_dict), function(z) {
+                    old_dict[z] = new_dict[z];
+                });
             } else {
                 this.exception("No enumerator given to foreach", context);
             }

doc/reference/qweb.rst

@@ -158,6 +158,26 @@ variables for various data points:
     a boolean flag indicating that the current iteration round is on an odd
     index
 
+
+These extra variables provided and all new variables created into the
+``foreach`` are only available in the scope of the``foreach``. If the
+variable exists outside the context of the ``foreach``, the value is copied
+at the end of the foreach into the global context.
+
+::
+
+    <t t-set="existing_variable" t-value="False"/>
+    <!-- existing_variable now False -->
+
+    <p t-foreach="[1, 2, 3]" t-as="i">
+        <t t-set="existing_variable" t-value="True"/>
+        <t t-set="new_variable" t-value="True"/>
+        <!-- existing_variable and new_variable now True -->
+    </p>
+
+    <!-- existing_variable always True -->
+    <!-- new_variable undefined -->
+
 .. _reference/qweb/attributes:
 
 attributes

openerp/addons/base/ir/ir_qweb.py

@@ -414,6 +414,10 @@ class QWeb(orm.AbstractModel):
                     '%s_odd' % varname: False,
                 })
             ru.append(self.render_element(element, template_attributes, generated_attributes, copy_qwebcontext))
+
+        for k in qwebcontext.keys():
+            qwebcontext[k] = copy_qwebcontext[k]
+
         return "".join(ru)
 
     def render_tag_if(self, element, template_attributes, generated_attributes, qwebcontext):