Result of SDL_GetGamepads must be de-allocated by SDL_free

[MattGuerrette]

This PR fixes a memory leak in the SDL3 backend where the gamepad list returned by SDL_GetGamepads was not being deallocated.

Noticed by running under the Xcode Instruments leak detector.

[ocornut]

See #7898
i believe you may need to update your copy of SDL

[MattGuerrette]

#7898

I am using mainline of the SDL repo, as my CMake fetch content script pulls down the latest.

You can see here: https://github.com/MattGuerrette/Metal/blob/db4360991f93a0c8ad68edd44f2d6853355f4274/cmake/FetchExternal.cmake#L23

Also, the mainline documentation of SDL3 now states:

/**
 * Get a list of currently connected gamepads.
 *
 * \param count a pointer filled in with the number of gamepads returned, may
 *              be NULL.
 * \returns a 0 terminated array of joystick instance IDs or NULL on failure;
 *          call SDL_GetError() for more information. This should be freed
 *          with SDL_free() when it is no longer needed.
 *
 * \since This function is available since SDL 3.0.0.
 *
 * \sa SDL_HasGamepad
 * \sa SDL_OpenGamepad
 */

[mgerhardy]

Unfortunately not: https://github.com/libsdl-org/SDL/blob/4961af4569eaaec8d2c9cbbd213236e6b7e2f1dd/include/SDL3/SDL_joystick.h#L216 - see the linked ticket there are more details.

[MattGuerrette]

Unfortunately not: https://github.com/libsdl-org/SDL/blob/4961af4569eaaec8d2c9cbbd213236e6b7e2f1dd/include/SDL3/SDL_joystick.h#L216 - see the linked ticket there are more details.

This is certainly a leak, as when should this be cleaned up then?

https://github.com/libsdl-org/SDL/blob/d9a5ed75b969af481a3da882ca87def205499513/src/joystick/SDL_joystick.c#L730

They are clearly allocating this joystick array and never freeing it. I don't think Xcode Instruments is confused about this at all.

I could file a ticket to SDL repo to fix that documentation, but for now I'd suggest doing what the SDL_Gamepad documentation clearly states and de-allocating this array:
https://github.com/libsdl-org/SDL/blob/d9a5ed75b969af481a3da882ca87def205499513/include/SDL3/SDL_gamepad.h#L473

[ocornut]

Looks like they made a large change to the memory system and then reverted it end of july, that explains things:
libsdl-org/SDL@4f55271

[ocornut]

Merged as 6a73195. Thank you!