Fix dangling reference in Character::gen_aim_mods_cache()

[BrettDong]

Summary

None

Purpose of change

Cataclysm-DDA/src/character.cpp

Lines 938 to 944 in 6807388

	aim_mods_cache Character::gen_aim_mods_cache( const item &gun )const
	{
	parallax_cache parallaxes{ get_character_parallax( true ), get_character_parallax( false ) };
	auto parallaxes_opt = std::make_optional( std::ref( parallaxes ) );
	aim_mods_cache aim_cache = { get_modifier( character_modifier_aim_speed_skill_mod, gun.gun_skill() ), get_modifier( character_modifier_aim_speed_dex_mod ), get_modifier( character_modifier_aim_speed_mod ), most_accurate_aiming_method_limit( gun ), aim_factor_from_volume( gun ), aim_factor_from_length( gun ), parallaxes_opt };
	return aim_cache;
	}

Character::gen_aim_mods_cache() stores a reference to the local variable parallaxes, causes a use-after-scope in subsequent aim speed calculations.

[brett] ~/Developer/Cataclysm-DDA [master]  % ./tests/cata_test unskilled_shooter_accuracy

22:34:33.469 INFO : SDL render devices: software, metal, opengl, opengles2
22:34:33.469 INFO : [options] C locale set to C
22:34:33.469 INFO : [options] C++ locale set to C
22:34:39.133 INFO : src/mod_tracker.h:68: Tried check if 'FakeSpecial_s_gas' had a duplicate, but type 'overmap_special' does not track object sources
22:35:01.319 INFO : Game data loaded, running Catch2 session:
Filters: unskilled_shooter_accuracy
=================================================================
==45065==ERROR: AddressSanitizer: stack-use-after-scope on address 0x00016fb189e4 at pc 0x000102812ab8 bp 0x00016fb18790 sp 0x00016fb18788
READ of size 4 at 0x00016fb189e4 thread T0
    #0 0x102812ab4 in Character::fastest_aiming_method_speed(item const&, double, Target_attributes, std::__1::optional<std::__1::reference_wrapper<parallax_cache>>) const character.cpp:988
    #1 0x102812f3c in Character::aim_per_move(item const&, double, Target_attributes, std::__1::optional<std::__1::reference_wrapper<aim_mods_cache const>>) const character.cpp:1100
    #2 0x104eb41ec in npc::aim(Target_attributes const&) npcmove.cpp:2300
    #3 0x101782168 in get_dispersion(npc&, int, int) ranged_balance_test.cpp:132
    #4 0x10177b3c0 in test_shooting_scenario(npc&, int, int, int) ranged_balance_test.cpp:163
    #5 0x101740b4c in ____C_A_T_C_H____T_E_S_T____37() ranged_balance_test.cpp:251
    #6 0x101bc01ec in Catch::RunContext::invokeActiveTestCase() catch.hpp:12997
    #7 0x101bbb528 in Catch::RunContext::runCurrentTest(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>&) catch.hpp:12970
    #8 0x101bb970c in Catch::RunContext::runTest(Catch::TestCase const&) catch.hpp:12731
    #9 0x101bc727c in Catch::Session::runInternal() catch.hpp:13530
    #10 0x101bc5bd8 in Catch::Session::run() catch.hpp:13486
    #11 0x101c0b424 in main test_main.cpp:405
    #12 0x18ecc10dc  (<unknown module>)

Address 0x00016fb189e4 is located in stack of thread T0 at offset 100 in frame
    #0 0x102812e04 in Character::aim_per_move(item const&, double, Target_attributes, std::__1::optional<std::__1::reference_wrapper<aim_mods_cache const>>) const character.cpp:1095

  This frame has 2 object(s):
    [32, 64) 'agg.tmp'
    [96, 112) 'gun_skill' (line 1115) <== Memory access at offset 100 is inside this variable
HINT: this may be a false positive if your program uses some custom stack unwind mechanism, swapcontext or vfork
      (longjmp and C++ exceptions *are* supported)
SUMMARY: AddressSanitizer: stack-use-after-scope character.cpp:988 in Character::fastest_aiming_method_speed(item const&, double, Target_attributes, std::__1::optional<std::__1::reference_wrapper<parallax_cache>>) const
Shadow bytes around the buggy address:
  0x00016fb18700: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x00016fb18780: 00 00 00 00 f1 f1 f1 f1 00 00 f2 f2 00 00 00 f2
  0x00016fb18800: f2 f2 f2 f2 f8 f8 f8 f3 f3 f3 f3 f3 00 00 00 00
  0x00016fb18880: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x00016fb18900: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
=>0x00016fb18980: f1 f1 f1 f1 00 00 00 00 f2 f2 f2 f2[f8]f8 f3 f3
  0x00016fb18a00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x00016fb18a80: 00 00 00 00 00 00 00 00 f1 f1 f1 f1 00 00 f2 f2
  0x00016fb18b00: 00 00 00 00 f2 f2 f2 f2 00 00 00 00 00 00 f2 f2
  0x00016fb18b80: f2 f2 f8 f2 f2 f2 00 00 00 00 f3 f3 f3 f3 f3 f3
  0x00016fb18c00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
Shadow byte legend (one shadow byte represents 8 application bytes):
  Addressable:           00
  Partially addressable: 01 02 03 04 05 06 07 
  Heap left redzone:       fa
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  Stack after return:      f5
  Stack use after scope:   f8
  Global redzone:          f9
  Global init order:       f6
  Poisoned by user:        f7
  Container overflow:      fc
  Array cookie:            ac
  Intra object redzone:    bb
  ASan internal:           fe
  Left alloca redzone:     ca
  Right alloca redzone:    cb
==45065==ABORTING
Stack trace at fatal error:


    Attempting to repeat stack trace using debug symbols…

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
cata_test is a Catch v2.13.7 host application.
Run with -? for options

-------------------------------------------------------------------------------
unskilled_shooter_accuracy
  an unskilled shooter with a common pistol
-------------------------------------------------------------------------------
../tests/ranged_balance_test.cpp:249
...............................................................................

../tests/ranged_balance_test.cpp:160: FAILED:
  {Unknown expression after the reported line}
due to a fatal error condition:
  SIGABRT - Abort (abnormal termination) signal

===============================================================================
test cases:  1 |  0 passed | 1 failed
assertions: 18 | 17 passed | 1 failed

zsh: abort      ./tests/cata_test unskilled_shooter_accuracy

Describe the solution

Make minimal code changes to avoid creating dangling references.

Describe alternatives you've considered

I am not sure if using std::optional<std::reference_wrapper<T> is really appropriate here, and this part of code might worth revisiting for a refactor in the future.

Testing

AddressSanitizer does not report error after this patch.

Additional context