simulation: don't ask user to choose a delivery solver when only one is configured

In order to make solving divergences easier, we sometimes don't need to
show the delivery solver (priority) field when the solver only allow
one.

bt5/erp5_simulation/SkinTemplateItem/portal_skins/erp5_simulation/Base_viewSimulationFieldLibrary/my_dialog_mode_solver_decision_delivery_solver.xml

@@ -10,8 +10,10 @@
             <key> <string>delegated_list</string> </key>
             <value>
               <list>
+                <string>css_class</string>
                 <string>default</string>
                 <string>external_validator</string>
+                <string>hidden</string>
                 <string>items</string>
                 <string>title</string>
               </list>
@@ -64,11 +66,17 @@
             <value>
               <dictionary>
                 <item>
-                    <key> <string>default</string> </key>
+                    <key> <string>css_class</string> </key>
                     <value>
                       <persistent> <string encoding="base64">AAAAAAAAAAI=</string> </persistent>
                     </value>
                 </item>
+                <item>
+                    <key> <string>default</string> </key>
+                    <value>
+                      <persistent> <string encoding="base64">AAAAAAAAAAM=</string> </persistent>
+                    </value>
+                </item>
                 <item>
                     <key> <string>external_validator</string> </key>
                     <value> <string></string> </value>
@@ -81,10 +89,16 @@
                     <key> <string>form_id</string> </key>
                     <value> <string></string> </value>
                 </item>
+                <item>
+                    <key> <string>hidden</string> </key>
+                    <value>
+                      <persistent> <string encoding="base64">AAAAAAAAAAQ=</string> </persistent>
+                    </value>
+                </item>
                 <item>
                     <key> <string>items</string> </key>
                     <value>
-                      <persistent> <string encoding="base64">AAAAAAAAAAM=</string> </persistent>
+                      <persistent> <string encoding="base64">AAAAAAAAAAU=</string> </persistent>
                     </value>
                 </item>
                 <item>
@@ -102,6 +116,10 @@
             <key> <string>values</string> </key>
             <value>
               <dictionary>
+                <item>
+                    <key> <string>css_class</string> </key>
+                    <value> <string></string> </value>
+                </item>
                 <item>
                     <key> <string>default</string> </key>
                     <value> <string></string> </value>
@@ -109,7 +127,7 @@
                 <item>
                     <key> <string>external_validator</string> </key>
                     <value>
-                      <persistent> <string encoding="base64">AAAAAAAAAAQ=</string> </persistent>
+                      <persistent> <string encoding="base64">AAAAAAAAAAY=</string> </persistent>
                     </value>
                 </item>
                 <item>
@@ -120,6 +138,10 @@
                     <key> <string>form_id</string> </key>
                     <value> <string>Base_viewFieldLibrary</string> </value>
                 </item>
+                <item>
+                    <key> <string>hidden</string> </key>
+                    <value> <int>0</int> </value>
+                </item>
                 <item>
                     <key> <string>items</string> </key>
                     <value>
@@ -152,7 +174,7 @@
       <dictionary>
         <item>
             <key> <string>_text</string> </key>
-            <value> <string>python:here.getConfigurationPropertyDict().get(\'delivery_solver\', None)</string> </value>
+            <value> <string>python: "hidden_label" if here.SolverDecision_getDefaultDeliverySolverIfUnique() else ""</string> </value>
         </item>
       </dictionary>
     </pickle>
@@ -165,12 +187,38 @@
       <dictionary>
         <item>
             <key> <string>_text</string> </key>
-            <value> <string>python:[(here.Base_translateString(x.getSolverActionTitle() or \'\'), x.getId()) for x in here.searchDeliverySolverList()]</string> </value>
+            <value> <string>python:here.getConfigurationPropertyDict().get(\'delivery_solver\') or here.SolverDecision_getDefaultDeliverySolverIfUnique()</string> </value>
         </item>
       </dictionary>
     </pickle>
   </record>
   <record id="4" aka="AAAAAAAAAAQ=">
+    <pickle>
+      <global name="TALESMethod" module="Products.Formulator.TALESField"/>
+    </pickle>
+    <pickle>
+      <dictionary>
+        <item>
+            <key> <string>_text</string> </key>
+            <value> <string>python: here.SolverDecision_getDefaultDeliverySolverIfUnique()</string> </value>
+        </item>
+      </dictionary>
+    </pickle>
+  </record>
+  <record id="5" aka="AAAAAAAAAAU=">
+    <pickle>
+      <global name="TALESMethod" module="Products.Formulator.TALESField"/>
+    </pickle>
+    <pickle>
+      <dictionary>
+        <item>
+            <key> <string>_text</string> </key>
+            <value> <string>python:[(here.Base_translateString(x.getSolverActionTitle() or \'\'), x.getId()) for x in here.searchDeliverySolverList()]</string> </value>
+        </item>
+      </dictionary>
+    </pickle>
+  </record>
+  <record id="6" aka="AAAAAAAAAAY=">
     <pickle>
       <global name="Method" module="Products.Formulator.MethodField"/>
     </pickle>

bt5/erp5_simulation/SkinTemplateItem/portal_skins/erp5_simulation/SolverDecision_getDefaultDeliverySolverIfUnique.py

+# type: () -> Optional[str]
+"""Returns the id of delivery solver if there's only one configured
+on this solver, None otherwise.
+"""
+delivery_solver_list = context.searchDeliverySolverList()
+if len(delivery_solver_list) == 1:
+  return delivery_solver_list[0].getId()

bt5/erp5_simulation/SkinTemplateItem/portal_skins/erp5_simulation/SolverDecision_getDefaultDeliverySolverIfUnique.xml

+<?xml version="1.0"?>
+<ZopeData>
+  <record id="1" aka="AAAAAAAAAAE=">
+    <pickle>
+      <global name="PythonScript" module="Products.PythonScripts.PythonScript"/>
+    </pickle>
+    <pickle>
+      <dictionary>
+        <item>
+            <key> <string>Script_magic</string> </key>
+            <value> <int>3</int> </value>
+        </item>
+        <item>
+            <key> <string>_bind_names</string> </key>
+            <value>
+              <object>
+                <klass>
+                  <global name="NameAssignments" module="Shared.DC.Scripts.Bindings"/>
+                </klass>
+                <tuple/>
+                <state>
+                  <dictionary>
+                    <item>
+                        <key> <string>_asgns</string> </key>
+                        <value>
+                          <dictionary>
+                            <item>
+                                <key> <string>name_container</string> </key>
+                                <value> <string>container</string> </value>
+                            </item>
+                            <item>
+                                <key> <string>name_context</string> </key>
+                                <value> <string>context</string> </value>
+                            </item>
+                            <item>
+                                <key> <string>name_m_self</string> </key>
+                                <value> <string>script</string> </value>
+                            </item>
+                            <item>
+                                <key> <string>name_subpath</string> </key>
+                                <value> <string>traverse_subpath</string> </value>
+                            </item>
+                          </dictionary>
+                        </value>
+                    </item>
+                  </dictionary>
+                </state>
+              </object>
+            </value>
+        </item>
+        <item>
+            <key> <string>_params</string> </key>
+            <value> <string></string> </value>
+        </item>
+        <item>
+            <key> <string>id</string> </key>
+            <value> <string>SolverDecision_getDefaultDeliverySolverIfUnique</string> </value>
+        </item>
+      </dictionary>
+    </pickle>
+  </record>
+</ZopeData>