Merge pull request CleverRaven#30212 from Night-Pryanik/on-roof-flag

Added ON_ROOF flag

data/mods/Aftershock/vehicles/afs_vehicle_parts.json

@@ -239,6 +239,7 @@
     "name": "roof-mounted external tank (200L)",
     "item": "55gal_drum",
     "location": "on_roof",
+    "flags": [ "ON_ROOF" ],
     "size": 200000
   },
   {

doc/JSON_FLAGS.md

@@ -537,6 +537,7 @@ These branches are also the valid entries for the categories of `dreams` in `dre
 - ```OBSTACLE``` Cannot walk through part, unless the part is also ```OPENABLE```.
 - ```ODDTURN``` Only on during odd turns.
 - ```ON_CONTROLS```
+- ```ON_ROOF``` - Parts with this flag could only be installed on a roof (parts with ```ROOF``` flag).
 - ```OPAQUE``` Cannot be seen through.
 - ```OPENABLE``` Can be opened or closed.
 - ```OPENCLOSE_INSIDE```  Can be opened or closed, but only from inside the vehicle.
@@ -568,7 +569,8 @@ These branches are also the valid entries for the categories of `dreams` in `dre
 - ```TOOL_WRENCH``` Attached with bolts, can be removed/installed with a wrench
 - ```TRACK``` Allows the vehicle installed on, to be marked and tracked on map.
 - ```TRACKED``` Contributes to steering effectiveness but doesn't count as a steering axle for install difficulty and still contributes to drag for the center of steering calculation.
-- ```TURRET``` Is a weapon turret.
+- ```TURRET``` Is a weapon turret. Can only be installed on a part with ```TURRET_MOUNT``` flag.
+- ```TURRET_MOUNT``` Parts with this flag are suitable for installing turrets.
 - ```UNMOUNT_ON_DAMAGE``` Part breaks off the vehicle when destroyed by damage.
 - ```UNMOUNT_ON_MOVE``` Dismount this part when the vehicle moves. Doesn't drop the part, unless you give it special handling.
 - ```VARIABLE_SIZE``` Has 'bigness' for power, wheel radius, etc.

src/vehicle.cpp

@@ -1015,7 +1015,7 @@ bool vehicle::can_mount( const point &dp, const vpart_id &id ) const
         }
     }
 
-    //Turret mounts must NOT be installed on other (moded) turret mounts
+    //Turret mounts must NOT be installed on other (modded) turret mounts
     if( part.has_flag( "TURRET_MOUNT" ) ) {
         for( const auto &elem : parts_in_square ) {
             if( part_info( elem ).has_flag( "TURRET_MOUNT" ) ) {
@@ -1024,6 +1024,20 @@ bool vehicle::can_mount( const point &dp, const vpart_id &id ) const
         }
     }
 
+    //Roof-mounted parts must be installed on a roofs
+    if( part.has_flag( "ON_ROOF" ) ) {
+        bool anchor_found = false;
+        for( const auto &elem : parts_in_square ) {
+            if( part_info( elem ).has_flag( "ROOF" ) ) {
+                anchor_found = true;
+                break;
+            }
+        }
+        if( !anchor_found ) {
+            return false;
+        }
+    }
+
     //Anything not explicitly denied is permitted
     return true;
 }