Gui: Add ability to disable single-solid rule by default

src/Gui/PreferencePages/DlgSettingsGeneral.cpp

@@ -712,4 +712,4 @@ void DlgSettingsGeneral::attachObserver()
     handlers.addHandler(ParamKey(hDockWindows->GetGroup("DAGView"), "Enabled"), applyDockWidget);
 }
 
-#include "moc_DlgSettingsGeneral.cpp"
+#include "moc_DlgSettingsGeneral.cpp"

src/Mod/Part/Gui/DlgSettingsGeneral.cpp

@@ -60,6 +60,7 @@ void DlgSettingsGeneral::saveSettings()
     ui->checkBooleanRefine->onSave();
     ui->checkSketchBaseRefine->onSave();
     ui->checkObjectNaming->onSave();
+    ui->checkAllowCompoundBody->onSave();
 }
 
 void DlgSettingsGeneral::loadSettings()
@@ -68,6 +69,7 @@ void DlgSettingsGeneral::loadSettings()
     ui->checkBooleanRefine->onRestore();
     ui->checkSketchBaseRefine->onRestore();
     ui->checkObjectNaming->onRestore();
+    ui->checkAllowCompoundBody->onRestore();
 }
 
 /**

src/Mod/Part/Gui/DlgSettingsGeneral.ui

@@ -13,8 +13,8 @@
   <property name="windowTitle">
    <string>General</string>
   </property>
-  <layout class="QGridLayout" name="gridLayout_3">
-   <item row="0" column="0">
+  <layout class="QVBoxLayout" name="verticalLayout">
+   <item>
     <widget class="QGroupBox" name="groupBox_2">
      <property name="title">
       <string>Model settings</string>
@@ -62,14 +62,17 @@
      </layout>
     </widget>
    </item>
-   <item row="1" column="0">
+   <item>
     <widget class="QGroupBox" name="groupBox_3">
-     <property name="title">
-      <string>Object naming</string>
+     <property name="enabled">
+      <bool>true</bool>
      </property>
      <property name="visible">
       <bool>false</bool>
      </property>
+     <property name="title">
+      <string>Object naming</string>
+     </property>
      <layout class="QGridLayout" name="gridLayout_2">
       <item row="0" column="0">
        <widget class="Gui::PrefCheckBox" name="checkObjectNaming">
@@ -87,7 +90,45 @@
      </layout>
     </widget>
    </item>
-   <item row="2" column="0">
+   <item>
+    <widget class="QGroupBox" name="groupBoxExperimental">
+     <property name="enabled">
+      <bool>true</bool>
+     </property>
+     <property name="title">
+      <string>Experimental</string>
+     </property>
+     <property name="flat">
+      <bool>false</bool>
+     </property>
+     <layout class="QVBoxLayout" name="verticalLayout_2">
+      <item>
+       <widget class="QLabel" name="warningLabel">
+        <property name="text">
+         <string>These settings are experimental and may result in decreased stability, more problems and undefined behaviors.</string>
+        </property>
+        <property name="wordWrap">
+         <bool>true</bool>
+        </property>
+       </widget>
+      </item>
+      <item>
+       <widget class="Gui::PrefCheckBox" name="checkAllowCompoundBody">
+        <property name="text">
+         <string>Allow multiple solids in Part Design Body by default (experimental)</string>
+        </property>
+        <property name="prefEntry" stdset="0">
+         <cstring>AllowCompoundDefault</cstring>
+        </property>
+        <property name="prefPath" stdset="0">
+         <cstring>Mod/PartDesign</cstring>
+        </property>
+       </widget>
+      </item>
+     </layout>
+    </widget>
+   </item>
+   <item>
     <spacer>
      <property name="orientation">
       <enum>Qt::Vertical</enum>

src/Mod/PartDesign/App/Feature.cpp

@@ -180,6 +180,12 @@ bool Feature::isSingleSolidRuleSatisfied(const TopoDS_Shape& shape, TopAbs_Shape
 Feature::SingleSolidRuleMode Feature::singleSolidRuleMode()
 {
     auto body = getFeatureBody();
+
+    // When the feature is not part of an body (which should not happen) let's stay with the default
+    if (!body) {
+        return SingleSolidRuleMode::Enforced;
+    }
+
     auto areCompoundSolidsAllowed = body->AllowCompound.getValue();
 
     return areCompoundSolidsAllowed ? SingleSolidRuleMode::Disabled : SingleSolidRuleMode::Enforced;