Prevent crash when lastworld.json is corrupted or empty.

[KheirFerrum]

Summary

SUMMARY: Bugfixes "Prevent crash when lastworld.json is corrupted or empty."

Purpose of change

Had an issue today where someone's computer didn't end the game appropriately, corrupting lastworld.json, this caused a crash that would consistently prevent the game from starting with no warning except crash log messages.

Describe the solution

Use try and catch to catch exceptions and report them when they occur loading lastworld.json

Describe alternatives you've considered

Testing

Need others to test for me, my computer is down. This should be tested via creating lastworld.json in the config folder. Either leave it empty or in various states of incomplete/wrong format.

Additional context

[scarf005]

moderately corrupt JSON

{
  "world_name": Very-Empty",
  "foo": [1,,2,3]
  "character_name": "Maribel Hearn"
}  

array in lastworld.json:

[]

empty lastworld.json:

corrupt options.json for comparison:

[adfs
  { "info": "If enabled, when your character dies, the player is given a prompt that gives the option to cancel savefile deletion and other death effects, returning to the main menu without saving instead.", "default": "Default: False", "name": "PROMPT_ON_CHARACTER_DEATH", "value": "true" },
(continues below)

---

the changes doesn't seem to work, could you have a look?

[KheirFerrum]

Dammit, will make draft, can't really do much with a notepad, so will have to wait until I get my computer back. Weird that test_object() isn't working at all.

[scarf005]

yeah strange. i think cata's JSON parser doesn't handle invalid JSONs very well in general, as seen on corrupt options.json

[olanti-p]

test_object only checks if an object is about to start (i.e. next character is {), it doesn't validate it or even check if there's a matching }.

According to the debugger, in some cases the game crashes because get_object() throws an exception when it tries and fails to parse the object, but that exception isn't caught by anything.

Other cases were caused by missing check in Lua backtrace code, that should be fixed by #3187

[KheirFerrum]

test_object only checks if an object is about to start (i.e. next character is {), it doesn't validate it or even check if there's a matching }.

According to the debugger, in some cases the game crashes because get_object() throws an exception when it tries and fails to parse the object, but that exception isn't caught by anything.

Other cases were caused by missing check in Lua backtrace code, that should be fixed by #3187

Then is there no way to prevent this from crashing? Or just deleting the file and restarting when it would otherwise crash?

[olanti-p]

You need to replace that if test_object { get_object } else { error } with try { get_object } catch { error }. test_object is useless here; get_object works perfectly - detects error and throws an exception, but because there's no code that catches the exception, it gets caught by the OS and the OS terminates the game.

[scarf005]

 DEBUG    : Json error: config/lastworld.json:2:23: missing comma

{
  "world_name": "Test"
                      ^
  "character_name": "Maribel Hearn"
}


 FUNCTION : void worldfactory::load_last_world_info()
 FILE     : /home/scarf/repo/cata/Cataclysm/src/worldfactory.cpp
 LINE     : 609
 VERSION  : BN 440e1342128

LGTM