Fix map_cursor containing local coordinates #40296
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The function `are_requirements_nearby` accesses `player::backlog::front()`, which causes UB when the `backlog` list is empty. This is usually checked by the caller, but there is at least one way to reach this function without that check: ``` #2 0x000000000083dfaa in string_id<activity_type>::operator== (rhs=..., this=0xdf1b460) at src/player_activity.h:93 #3 are_requirements_nearby (loot_spots=std::vector of length 21, capacity 32 = {...}, needed_things=..., p=..., activity_to_restore=..., in_loot_zones=true, src_loc=...) at src/activity_item_handling.cpp:1113 CleverRaven#4 0x0000000000843a46 in generic_multi_activity_check_requirement (p=..., act_id=..., act_info=..., src=..., src_loc=..., src_set=std::unordered_set with 1 element = {...}, check_only=false) at src/activity_item_handling.cpp:2676 CleverRaven#5 0x0000000000852813 in generic_multi_activity_handler (act=..., p=..., check_only=check_only@entry=false) at src/activity_item_handling.cpp:2885 CleverRaven#6 0x0000000000800896 in activity_handlers::multiple_butcher_do_turn (act=<optimized out>, p=<optimized out>) at src/activity_handlers.cpp:3822 CleverRaven#7 0x000000000082b248 in std::_Function_handler<void (player_activity*, player*), void (*)(player_activity*, player*)>::_M_invoke(std::_Any_data const&, player_activity*&&, player*&&) (__functor=..., __args#0=<optimized out>, __args#1=<optimized out>) at /usr/include/c++/8/bits/std_function.h:88 CleverRaven#8 0x00000000008630e3 in std::function<void (player_activity*, player*)>::operator()(player_activity*, player*) const (this=<optimized out>, __args#0=<optimized out>, __args#0@entry=0xdf1b330, __args#1=<optimized out>, __args#1@entry=0xdf1ae50) at /usr/include/c++/8/bits/std_function.h:260 CleverRaven#9 0x0000000000860306 in activity_type::call_do_turn (this=0x2c3c930, act=act@entry=0xdf1b330, p=p@entry=0xdf1ae50) at src/activity_type.cpp:118 CleverRaven#10 0x00000000014a968b in player_activity::do_turn (this=this@entry=0xdf1b330, p=...) at src/player_activity.cpp:237 CleverRaven#11 0x00000000013092a4 in npc::do_player_activity (this=this@entry=0xdf1ae50) at src/npcmove.cpp:3299 CleverRaven#12 0x0000000001322a07 in npc::execute_action (this=this@entry=0xdf1ae50, action=<optimized out>, action@entry=npc_player_activity) at src/npcmove.cpp:1237 CleverRaven#13 0x000000000132690a in npc::move (this=this@entry=0xdf1ae50) at src/npcmove.cpp:907 ``` This adds a simple check within the function.
`map_cursor` is used in `item_location`, which in turn is used by the `player_activity`, which in turn is used by NPCs. So if you ask an NPC to butcher something, it will move to the corpse and "wait" there (won't move until the butchering is done). This stores are references to the corpse via an `item_location` (and the contained `map_cursor`), which means it stores the **local** coordinates of the corpse. If you move far enough away, so the map shifts, those coordinates are now pointing to a different location. Consequently, when the butchering finishes, it will try to remove the corpse from the wrong place. I fixed this with the smallest amount of code changes possible. But it's not a good fix. Better would be to access the `tripoint` via dedicated getters. This may also fix some other bugs that display a "Tried to remove item from object which did not contain it" message.
ZhilkinSerg
added
<Bugfix>
This was referenced May 10, 2020
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