Add trigger action for forming a one-way alliance

src/spawner/spawner.asm

@@ -601,9 +601,11 @@ _Init_Game_Check_Spawn_Arg_No_Intro:
 
 _HouseClass__Make_Ally_STFU_when_Allying_In_Loading_Screen_Spawner:
     cmp byte [IsDoingAlliancesSpawner], 1
-    jz 0x004BDE68
-    test al, al          ; hooked by patch
-    jz 0x4BDE68
+    je  0x004BDE68
+    cmp byte [AlliesAllowed], 0
+    je  0x004BDE68
+    test al, al          ; fix code that our jump-to-hook destroyed
+    jz  0x004BDE68
     jmp 0x004BDDB9
 
 _SessionClass__Free_Scenario_Descriptions_RETN_Patch:

src/trigger_actions_extended.asm

@@ -161,6 +161,8 @@ hack 0x0061913B ; Extend trigger action jump table
     jz .Remove_Attached_Objects_Action
     cmp edx, 115
     jz .Assign_Mission_To_All_Units_Action
+    cmp edx, 116
+    jz .Make_Ally_One_Sided_Action
 
     cmp edx, 68h
     ja 0x0061A9C5 ; default
@@ -419,3 +421,24 @@ hack 0x0061913B ; Extend trigger action jump table
     jl    .AM_Loop_MainBody
     jmp   0x00619F9F ; success
 
+
+
+; ***********************************
+; ***    Make Ally (One-Sided)    ***
+; ***********************************
+.Make_Ally_One_Sided_Action:
+    mov     ecx, [esi+40h]  ; Fetch first parameter
+    cmp     ecx, 0FFFFFFFFh
+    jz      0x00619F9F      ; success
+    call    0x004C4730      ; HouseClass::As_Pointer(HousesType)
+    mov     ecx, [esp+1C4h] ; Fetch owning house from trigger data
+    push    eax
+    ; We need to increment ScenarioInit to allow houses to ally even if they would be the "last enemies" to each other in multiplayer
+    mov     edi, [ScenarioInit]
+    inc     edi
+    mov     [ScenarioInit], edi
+    call    0x004BDB50      ; HouseClass::Make_Ally(HouseClass *)
+    mov     edi, [ScenarioInit]
+    dec     edi
+    mov     [ScenarioInit], edi
+    jmp     0x00619F9F      ; success