Introduce formal policy for APIs that return strings.

This declares that any `const char *` returned from SDL is owned by SDL, and
promises to be valid _at least_ until the next time the event queue runs, or
SDL_Quit() is called, even if the thing that owns the string gets destroyed
or changed before then.

This is noted in the headers as "the SDL_GetStringRule", so this will both be
greppable to find a detailed explaination in docs/README-strings.md and
wikiheaders will automatically turn it into a link we can point at the
appropriate documentation.

Fixes #9902.

(and several FIXMEs, both known and yet-undocumented.)

src/SDL.c

@@ -573,10 +573,11 @@ int SDL_GetVersion(void)
 /* Get the library source revision */
 const char *SDL_GetRevision(void)
 {
-    return SDL_REVISION;
+    return SDL_REVISION;  // a string literal, no need to SDL_FreeLater it.
 }
 
-/* Get the name of the platform */
+// Get the name of the platform
+// (a string literal, no need to SDL_FreeLater it.)
 const char *SDL_GetPlatform(void)
 {
 #if defined(SDL_PLATFORM_AIX)

src/SDL_hints.c

@@ -74,9 +74,7 @@ SDL_bool SDL_SetHintWithPriority(const char *name, const char *value, SDL_HintPr
                     entry->callback(entry->userdata, name, old_value, value);
                     entry = next;
                 }
-                if (old_value) {
-                    SDL_free(old_value);
-                }
+                SDL_FreeLater(old_value);
             }
             hint->priority = priority;
             return SDL_TRUE;
@@ -120,7 +118,7 @@ SDL_bool SDL_ResetHint(const char *name)
                     entry = next;
                 }
             }
-            SDL_free(hint->value);
+            SDL_FreeLater(hint->value);
             hint->value = NULL;
             hint->priority = SDL_HINT_DEFAULT;
             return SDL_TRUE;
@@ -147,7 +145,7 @@ void SDL_ResetHints(void)
                 entry = next;
             }
         }
-        SDL_free(hint->value);
+        SDL_FreeLater(hint->value);
         hint->value = NULL;
         hint->priority = SDL_HINT_DEFAULT;
     }
@@ -305,7 +303,7 @@ void SDL_ClearHints(void)
         SDL_hints = hint->next;
 
         SDL_free(hint->name);
-        SDL_free(hint->value);
+        SDL_FreeLater(hint->value);
         for (entry = hint->callbacks; entry;) {
             SDL_HintWatch *freeable = entry;
             entry = entry->next;

src/SDL_internal.h

@@ -293,6 +293,13 @@ extern int SDLCALL SDL_WaitSemaphoreTimeoutNS(SDL_Semaphore *sem, Sint64 timeout
 extern int SDLCALL SDL_WaitConditionTimeoutNS(SDL_Condition *cond, SDL_Mutex *mutex, Sint64 timeoutNS);
 extern SDL_bool SDLCALL SDL_WaitEventTimeoutNS(SDL_Event *event, Sint64 timeoutNS);
 
+/* Queue `memory` to be passed to SDL_free once the event queue is emptied.
+   this manages the list of pointers to SDL_AllocateEventMemory, but you
+   can use it to queue pointers from other subsystems that can die at any
+   moment but definitely need to live long enough for the app to copy them
+   if they happened to query them in their last moments. */
+extern void *SDL_FreeLater(void *memory);
+
 /* Ends C function definitions when using C++ */
 #ifdef __cplusplus
 }

src/SDL_properties.c

@@ -65,14 +65,12 @@ static void SDL_FreePropertyWithCleanup(const void *key, const void *value, void
             }
             break;
         case SDL_PROPERTY_TYPE_STRING:
-            SDL_free(property->value.string_value);
+            SDL_FreeLater(property->value.string_value);  // this pointer might be given to the app by SDL_GetStringProperty.
             break;
         default:
             break;
         }
-        if (property->string_storage) {
-            SDL_free(property->string_storage);
-        }
+        SDL_FreeLater(property->string_storage);  // this pointer might be given to the app by SDL_GetStringProperty.
     }
     SDL_free((void *)key);
     SDL_free((void *)value);
@@ -552,12 +550,6 @@ const char *SDL_GetStringProperty(SDL_PropertiesID props, const char *name, cons
         return value;
     }
 
-    /* Note that taking the lock here only guarantees that we won't read the
-     * hashtable while it's being modified. The value itself can easily be
-     * freed from another thread after it is returned here.
-     *
-     * FIXME: Should we SDL_strdup() the return value to avoid this?
-     */
     SDL_LockMutex(properties->lock);
     {
         SDL_Property *property = NULL;

src/audio/SDL_audio.c

@@ -131,6 +131,7 @@ int SDL_GetNumAudioDrivers(void)
     return num_drivers;
 }
 
+// this returns string literals, so there's no need to use SDL_FreeLater.
 const char *SDL_GetAudioDriver(int index)
 {
     if (index >= 0 && index < SDL_GetNumAudioDrivers()) {
@@ -139,6 +140,7 @@ const char *SDL_GetAudioDriver(int index)
     return NULL;
 }
 
+// this returns string literals, so there's no need to use SDL_FreeLater.
 const char *SDL_GetCurrentAudioDriver(void)
 {
     return current_audio.name;
@@ -521,7 +523,7 @@ static void DestroyPhysicalAudioDevice(SDL_AudioDevice *device)
     SDL_DestroyMutex(device->lock);
     SDL_DestroyCondition(device->close_cond);
     SDL_free(device->work_buffer);
-    SDL_free(device->name);
+    SDL_FreeLater(device->name);  // this pointer is handed to the app during SDL_GetAudioDeviceName
     SDL_free(device);
 }
 
@@ -1402,12 +1404,12 @@ SDL_AudioDevice *SDL_FindPhysicalAudioDeviceByHandle(void *handle)
     return SDL_FindPhysicalAudioDeviceByCallback(TestDeviceHandleCallback, handle);
 }
 
-char *SDL_GetAudioDeviceName(SDL_AudioDeviceID devid)
+const char *SDL_GetAudioDeviceName(SDL_AudioDeviceID devid)
 {
-    char *retval = NULL;
+    const char *retval = NULL;
     SDL_AudioDevice *device = ObtainPhysicalAudioDevice(devid);
     if (device) {
-        retval = SDL_strdup(device->name);
+        retval = device->name;
     }
     ReleaseAudioDevice(device);
 

src/camera/SDL_camera.c

@@ -63,6 +63,7 @@ int SDL_GetNumCameraDrivers(void)
     return SDL_arraysize(bootstrap) - 1;
 }
 
+// this returns string literals, so there's no need to use SDL_FreeLater.
 const char *SDL_GetCameraDriver(int index)
 {
     if (index >= 0 && index < SDL_GetNumCameraDrivers()) {
@@ -71,6 +72,7 @@ const char *SDL_GetCameraDriver(int index)
     return NULL;
 }
 
+// this returns string literals, so there's no need to use SDL_FreeLater.
 const char *SDL_GetCurrentCameraDriver(void)
 {
     return camera_driver.name;

src/core/SDL_core_unsupported.c

@@ -141,7 +141,7 @@ int SDL_AndroidGetExternalStorageState(Uint32 *state)
     return SDL_Unsupported();
 }
 SDL_DECLSPEC const char *SDLCALL SDL_AndroidGetInternalStoragePath(void);
-const char *SDL_AndroidGetInternalStoragePath()
+const char *SDL_AndroidGetInternalStoragePath(void)
 {
     SDL_Unsupported();
     return NULL;

src/core/android/SDL_android.c

@@ -2417,6 +2417,7 @@ void SDL_AndroidBackButton(void)
     (*env)->CallStaticVoidMethod(env, mActivityClass, midManualBackButton);
 }
 
+// this caches a string until the process ends, so there's no need to use SDL_FreeLater.
 const char *SDL_AndroidGetInternalStoragePath(void)
 {
     static char *s_AndroidInternalFilesPath = NULL;
@@ -2516,6 +2517,7 @@ int SDL_AndroidGetExternalStorageState(Uint32 *state)
     return 0;
 }
 
+// this caches a string until the process ends, so there's no need to use SDL_FreeLater.
 const char *SDL_AndroidGetExternalStoragePath(void)
 {
     static char *s_AndroidExternalFilesPath = NULL;

src/dynapi/SDL_dynapi_procs.h

@@ -213,7 +213,7 @@ SDL_DYNAPI_PROC(SDL_AssertionHandler,SDL_GetAssertionHandler,(void **a),(a),retu
 SDL_DYNAPI_PROC(const SDL_AssertData*,SDL_GetAssertionReport,(void),(),return)
 SDL_DYNAPI_PROC(SDL_AudioDeviceID*,SDL_GetAudioCaptureDevices,(int *a),(a),return)
 SDL_DYNAPI_PROC(int,SDL_GetAudioDeviceFormat,(SDL_AudioDeviceID a, SDL_AudioSpec *b, int *c),(a,b,c),return)
-SDL_DYNAPI_PROC(char*,SDL_GetAudioDeviceName,(SDL_AudioDeviceID a),(a),return)
+SDL_DYNAPI_PROC(const char*,SDL_GetAudioDeviceName,(SDL_AudioDeviceID a),(a),return)
 SDL_DYNAPI_PROC(const char*,SDL_GetAudioDriver,(int a),(a),return)
 SDL_DYNAPI_PROC(SDL_AudioDeviceID*,SDL_GetAudioOutputDevices,(int *a),(a),return)
 SDL_DYNAPI_PROC(int,SDL_GetAudioStreamAvailable,(SDL_AudioStream *a),(a),return)

src/events/SDL_events.c

@@ -108,37 +108,40 @@ static SDL_Mutex *SDL_event_memory_lock;
 static SDL_EventMemory *SDL_event_memory_head;
 static SDL_EventMemory *SDL_event_memory_tail;
 
-void *SDL_AllocateEventMemory(size_t size)
+void *SDL_FreeLater(void *memory)
 {
-    void *memory = SDL_malloc(size);
-    if (!memory) {
+    if (memory == NULL) {
         return NULL;
     }
 
+    SDL_EventMemory *entry = (SDL_EventMemory *)SDL_malloc(sizeof(*entry));
+    if (!entry) {
+        return memory;  // this is now a leak, but you probably have bigger problems if malloc failed. We could probably pool up and reuse entries, though.
+    }
+
     SDL_LockMutex(SDL_event_memory_lock);
     {
-        SDL_EventMemory *entry = (SDL_EventMemory *)SDL_malloc(sizeof(*entry));
-        if (entry) {
-            entry->eventID = SDL_last_event_id;
-            entry->memory = memory;
-            entry->next = NULL;
+        entry->eventID = SDL_last_event_id;
+        entry->memory = memory;
+        entry->next = NULL;
 
-            if (SDL_event_memory_tail) {
-                SDL_event_memory_tail->next = entry;
-            } else {
-                SDL_event_memory_head = entry;
-            }
-            SDL_event_memory_tail = entry;
+        if (SDL_event_memory_tail) {
+            SDL_event_memory_tail->next = entry;
         } else {
-            SDL_free(memory);
-            memory = NULL;
+            SDL_event_memory_head = entry;
         }
+        SDL_event_memory_tail = entry;
     }
     SDL_UnlockMutex(SDL_event_memory_lock);
 
     return memory;
 }
 
+void *SDL_AllocateEventMemory(size_t size)
+{
+    return SDL_FreeLater(SDL_malloc(size));
+}
+
 static void SDL_FlushEventMemory(Uint32 eventID)
 {
     SDL_LockMutex(SDL_event_memory_lock);

src/events/SDL_keyboard.c

@@ -742,7 +742,7 @@ void SDL_RemoveKeyboard(SDL_KeyboardID keyboardID, SDL_bool send_event)
         return;
     }
 
-    SDL_free(SDL_keyboards[keyboard_index].name);
+    SDL_FreeLater(SDL_keyboards[keyboard_index].name);
 
     if (keyboard_index != SDL_keyboard_count - 1) {
         SDL_memcpy(&SDL_keyboards[keyboard_index], &SDL_keyboards[keyboard_index + 1], (SDL_keyboard_count - keyboard_index - 1) * sizeof(SDL_keyboards[keyboard_index]));
@@ -1334,6 +1334,7 @@ SDL_Scancode SDL_GetScancodeFromKey(SDL_Keycode key)
     return SDL_SCANCODE_UNKNOWN;
 }
 
+// these are static memory, so we don't use SDL_FreeLater on them.
 const char *SDL_GetScancodeName(SDL_Scancode scancode)
 {
     const char *name;
@@ -1374,7 +1375,7 @@ SDL_Scancode SDL_GetScancodeFromName(const char *name)
 
 const char *SDL_GetKeyName(SDL_Keycode key)
 {
-    static char name[8];
+    char name[8];
     char *end;
 
     if (key & SDLK_SCANCODE_MASK) {
@@ -1405,7 +1406,7 @@ const char *SDL_GetKeyName(SDL_Keycode key)
 
         end = SDL_UCS4ToUTF8((Uint32)key, name);
         *end = '\0';
-        return name;
+        return SDL_FreeLater(SDL_strdup(name));
     }
 }
 

src/events/SDL_mouse.c

@@ -288,7 +288,7 @@ void SDL_RemoveMouse(SDL_MouseID mouseID, SDL_bool send_event)
         return;
     }
 
-    SDL_free(SDL_mice[mouse_index].name);
+    SDL_FreeLater(SDL_mice[mouse_index].name);  // SDL_GetMouseInstanceName returns this pointer.
 
     if (mouse_index != SDL_mouse_count - 1) {
         SDL_memcpy(&SDL_mice[mouse_index], &SDL_mice[mouse_index + 1], (SDL_mouse_count - mouse_index - 1) * sizeof(SDL_mice[mouse_index]));

src/events/SDL_touch.c

@@ -493,7 +493,7 @@ void SDL_DelTouch(SDL_TouchID id)
         SDL_free(touch->fingers[i]);
     }
     SDL_free(touch->fingers);
-    SDL_free(touch->name);
+    SDL_FreeLater(touch->name);  // this pointer might be given to the app by SDL_GetTouchDeviceName.
     SDL_free(touch);
 
     SDL_num_touch--;

src/filesystem/winrt/SDL_sysfilesystem.cpp

@@ -93,6 +93,7 @@ static const wchar_t *SDL_WinRTGetFSPathUNICODE(SDL_WinRT_Path pathType)
     return NULL;
 }
 
+// this caches a string until the process ends, so there's no need to use SDL_FreeLater.
 extern "C" const char *SDL_WinRTGetFSPath(SDL_WinRT_Path pathType)
 {
     typedef unordered_map<SDL_WinRT_Path, string> UTF8PathMap;

src/haptic/SDL_haptic.c

@@ -100,7 +100,7 @@ const char *SDL_GetHapticInstanceName(SDL_HapticID instance_id)
     if (SDL_GetHapticIndex(instance_id, &device_index)) {
         name = SDL_SYS_HapticName(device_index);
     }
-    return name;
+    return name ? SDL_FreeLater(SDL_strdup(name)) : NULL;
 }
 
 SDL_Haptic *SDL_OpenHaptic(SDL_HapticID instance_id)
@@ -338,7 +338,7 @@ void SDL_CloseHaptic(SDL_Haptic *haptic)
     }
 
     /* Free the data associated with this device */
-    SDL_free(haptic->name);
+    SDL_FreeLater(haptic->name);  // this pointer is handed to the app in SDL_GetHapticName()
     SDL_free(haptic);
 }
 

src/joystick/SDL_gamepad.c

@@ -1594,7 +1594,7 @@ static GamepadMapping_t *SDL_PrivateAddMappingForGUID(SDL_JoystickGUID jGUID, co
         /* Only overwrite the mapping if the priority is the same or higher. */
         if (pGamepadMapping->priority <= priority) {
             /* Update existing mapping */
-            SDL_free(pGamepadMapping->name);
+            SDL_FreeLater(pGamepadMapping->name);  // this is returned in SDL_GetGamepadName.
             pGamepadMapping->name = pchName;
             SDL_free(pGamepadMapping->mapping);
             pGamepadMapping->mapping = pchMapping;
@@ -3413,7 +3413,8 @@ const char * SDL_GetGamepadSerial(SDL_Gamepad *gamepad)
     if (!joystick) {
         return NULL;
     }
-    return SDL_GetJoystickSerial(joystick);
+    return SDL_GetJoystickSerial(joystick);  // this already returns a SDL_FreeLater pointer.
+
 }
 
 Uint64 SDL_GetGamepadSteamHandle(SDL_Gamepad *gamepad)
@@ -3680,7 +3681,7 @@ void SDL_QuitGamepadMappings(void)
     while (s_pSupportedGamepads) {
         pGamepadMap = s_pSupportedGamepads;
         s_pSupportedGamepads = s_pSupportedGamepads->next;
-        SDL_free(pGamepadMap->name);
+        SDL_FreeLater(pGamepadMap->name);  // this is returned in SDL_GetGamepadName.
         SDL_free(pGamepadMap->mapping);
         SDL_free(pGamepadMap);
     }
@@ -3826,8 +3827,8 @@ void SDL_GamepadHandleDelayedGuideButton(SDL_Joystick *joystick)
 const char *SDL_GetGamepadAppleSFSymbolsNameForButton(SDL_Gamepad *gamepad, SDL_GamepadButton button)
 {
 #ifdef SDL_JOYSTICK_MFI
-    const char *IOS_GetAppleSFSymbolsNameForButton(SDL_Gamepad *gamepad, SDL_GamepadButton button);
-    const char *retval;
+    char *IOS_GetAppleSFSymbolsNameForButton(SDL_Gamepad *gamepad, SDL_GamepadButton button);
+    char *retval;
 
     SDL_LockJoysticks();
     {
@@ -3837,9 +3838,11 @@ const char *SDL_GetGamepadAppleSFSymbolsNameForButton(SDL_Gamepad *gamepad, SDL_
     }
     SDL_UnlockJoysticks();
 
+    // retval was malloc'd by IOS_GetAppleSFSymbolsNameForButton
     if (retval && *retval) {
-        return retval;
+        return SDL_FreeLater(retval);
     }
+    SDL_free(retval);
 #endif
     return NULL;
 }
@@ -3847,8 +3850,8 @@ const char *SDL_GetGamepadAppleSFSymbolsNameForButton(SDL_Gamepad *gamepad, SDL_
 const char *SDL_GetGamepadAppleSFSymbolsNameForAxis(SDL_Gamepad *gamepad, SDL_GamepadAxis axis)
 {
 #ifdef SDL_JOYSTICK_MFI
-    const char *IOS_GetAppleSFSymbolsNameForAxis(SDL_Gamepad *gamepad, SDL_GamepadAxis axis);
-    const char *retval;
+    char *IOS_GetAppleSFSymbolsNameForAxis(SDL_Gamepad *gamepad, SDL_GamepadAxis axis);
+    char *retval;
 
     SDL_LockJoysticks();
     {
@@ -3858,9 +3861,11 @@ const char *SDL_GetGamepadAppleSFSymbolsNameForAxis(SDL_Gamepad *gamepad, SDL_Ga
     }
     SDL_UnlockJoysticks();
 
+    // retval was malloc'd by IOS_GetAppleSFSymbolsNameForAxis
     if (retval && *retval) {
-        return retval;
+        return SDL_FreeLater(retval);
     }
+    SDL_free(retval);
 #endif
     return NULL;
 }

src/joystick/SDL_joystick.c

@@ -785,8 +785,7 @@ const char *SDL_GetJoystickInstanceName(SDL_JoystickID instance_id)
     }
     SDL_UnlockJoysticks();
 
-    /* FIXME: Really we should reference count this name so it doesn't go away after unlock */
-    return name;
+    return name ? SDL_FreeLater(SDL_strdup(name)) : NULL;
 }
 
 /*
@@ -804,11 +803,10 @@ const char *SDL_GetJoystickInstancePath(SDL_JoystickID instance_id)
     }
     SDL_UnlockJoysticks();
 
-    /* FIXME: Really we should reference count this path so it doesn't go away after unlock */
     if (!path) {
         SDL_Unsupported();
     }
-    return path;
+    return path ? SDL_FreeLater(SDL_strdup(path)) : NULL;
 }
 
 /*
@@ -1663,7 +1661,6 @@ const char *SDL_GetJoystickName(SDL_Joystick *joystick)
     }
     SDL_UnlockJoysticks();
 
-    /* FIXME: Really we should reference count this name so it doesn't go away after unlock */
     return retval;
 }
 
@@ -1888,9 +1885,9 @@ void SDL_CloseJoystick(SDL_Joystick *joystick)
         }
 
         /* Free the data associated with this joystick */
-        SDL_free(joystick->name);
-        SDL_free(joystick->path);
-        SDL_free(joystick->serial);
+        SDL_FreeLater(joystick->name);  // SDL_GetJoystickName returns this pointer.
+        SDL_FreeLater(joystick->path);  // SDL_GetJoystickPath returns this pointer.
+        SDL_FreeLater(joystick->serial);  // SDL_GetJoystickSerial returns this pointer.
         SDL_free(joystick->axes);
         SDL_free(joystick->balls);
         SDL_free(joystick->hats);

src/joystick/apple/SDL_mfijoystick.m

@@ -1916,11 +1916,11 @@ static GCControllerDirectionPad *GetDirectionalPadForController(GCController *co
 }
 #endif /* SDL_JOYSTICK_MFI && ENABLE_PHYSICAL_INPUT_PROFILE */
 
-static char elementName[256];
-
-const char *IOS_GetAppleSFSymbolsNameForButton(SDL_Gamepad *gamepad, SDL_GamepadButton button)
+char *IOS_GetAppleSFSymbolsNameForButton(SDL_Gamepad *gamepad, SDL_GamepadButton button)
 {
+    char elementName[256];
     elementName[0] = '\0';
+
 #if defined(SDL_JOYSTICK_MFI) && defined(ENABLE_PHYSICAL_INPUT_PROFILE)
     if (gamepad && SDL_GetGamepadJoystick(gamepad)->driver == &SDL_IOS_JoystickDriver) {
         if (@available(macOS 10.16, iOS 14.0, tvOS 14.0, *)) {
@@ -2030,12 +2030,15 @@ const char *IOS_GetAppleSFSymbolsNameForButton(SDL_Gamepad *gamepad, SDL_Gamepad
         }
     }
 #endif
-    return elementName;
+
+    return SDL_strdup(elementName);
 }
 
-const char *IOS_GetAppleSFSymbolsNameForAxis(SDL_Gamepad *gamepad, SDL_GamepadAxis axis)
+char *IOS_GetAppleSFSymbolsNameForAxis(SDL_Gamepad *gamepad, SDL_GamepadAxis axis)
 {
+    char elementName[256];
     elementName[0] = '\0';
+
 #if defined(SDL_JOYSTICK_MFI) && defined(ENABLE_PHYSICAL_INPUT_PROFILE)
     if (gamepad && SDL_GetGamepadJoystick(gamepad)->driver == &SDL_IOS_JoystickDriver) {
         if (@available(macOS 10.16, iOS 14.0, tvOS 14.0, *)) {
@@ -2068,7 +2071,7 @@ const char *IOS_GetAppleSFSymbolsNameForAxis(SDL_Gamepad *gamepad, SDL_GamepadAx
         }
     }
 #endif
-    return *elementName ? elementName : NULL;
+    return *elementName ? SDL_strdup(elementName) : NULL;
 }
 
 SDL_JoystickDriver SDL_IOS_JoystickDriver = {

src/render/SDL_render.c

@@ -780,6 +780,7 @@ int SDL_GetNumRenderDrivers(void)
 #endif
 }
 
+// this returns string literals, so there's no need to use SDL_FreeLater.
 const char *SDL_GetRenderDriver(int index)
 {
 #ifndef SDL_RENDER_DISABLED

src/sensor/SDL_sensor.c

@@ -250,8 +250,7 @@ const char *SDL_GetSensorInstanceName(SDL_SensorID instance_id)
     }
     SDL_UnlockSensors();
 
-    /* FIXME: Really we should reference count this name so it doesn't go away after unlock */
-    return name;
+    return name ? SDL_FreeLater(SDL_strdup(name)) : NULL;
 }
 
 SDL_SensorType SDL_GetSensorInstanceType(SDL_SensorID instance_id)
@@ -527,7 +526,7 @@ void SDL_CloseSensor(SDL_Sensor *sensor)
         }
 
         /* Free the data associated with this sensor */
-        SDL_free(sensor->name);
+        SDL_FreeLater(sensor->name);  // this pointer gets handed to the app by SDL_GetSensorName().
         SDL_free(sensor);
     }
     SDL_UnlockSensors();

src/thread/SDL_thread.c

@@ -299,9 +299,7 @@ void SDL_RunThread(SDL_Thread *thread)
     if (!SDL_AtomicCompareAndSwap(&thread->state, SDL_THREAD_STATE_ALIVE, SDL_THREAD_STATE_ZOMBIE)) {
         /* Clean up if something already detached us. */
         if (SDL_AtomicCompareAndSwap(&thread->state, SDL_THREAD_STATE_DETACHED, SDL_THREAD_STATE_CLEANED)) {
-            if (thread->name) {
-                SDL_free(thread->name);
-            }
+            SDL_FreeLater(thread->name);
             SDL_free(thread);
         }
     }
@@ -421,9 +419,7 @@ void SDL_WaitThread(SDL_Thread *thread, int *status)
         if (status) {
             *status = thread->status;
         }
-        if (thread->name) {
-            SDL_free(thread->name);
-        }
+        SDL_FreeLater(thread->name);
         SDL_free(thread);
     }
 }

src/video/SDL_pixels.c

@@ -85,6 +85,7 @@ Uint16 SDL_expand_byte10[] = {
 
 /* Helper functions */
 
+// This doesn't need SDL_FreeLater since it returns string literals.
 #define CASE(X) \
     case X:     \
         return #X;

src/video/SDL_video.c

@@ -498,6 +498,7 @@ int SDL_GetNumVideoDrivers(void)
     return SDL_arraysize(bootstrap) - 1;
 }
 
+// this returns string literals, so there's no need to use SDL_FreeLater.
 const char *SDL_GetVideoDriver(int index)
 {
     if (index >= 0 && index < SDL_GetNumVideoDrivers()) {
@@ -642,6 +643,7 @@ pre_driver_error:
     return -1;
 }
 
+// this returns string literals, so there's no need to use SDL_FreeLater.
 const char *SDL_GetCurrentVideoDriver(void)
 {
     if (!_this) {