When compiling as C++20, MOZ_CONSTINIT expands to constinit. Since gNumNormalOrHighPriorityQueuesHaveTaskScheduledMainThread's extern declaration in WebTaskScheduler.h was declared constinit, the definition in WebTaskSchedulerMainThread.cpp must also be constinit (MOZ_CONSTINIT).
dom/webscheduling/WebTaskSchedulerMainThread.cpp:15:10: error: 'constinit' specifier missing on initializing declaration of 'gNumNormalOrHighPriorityQueuesHaveTaskScheduledMainThread' [-Werror,-Wmissing-constinit]
15 | uint32_t gNumNormalOrHighPriorityQueuesHaveTaskScheduledMainThread = 0;
| ^
dom/webscheduling/WebTaskScheduler.h:27:1: note: variable declared constinit here
27 | MOZ_CONSTINIT extern uint32_t
| ^
Differential Revision: https://phabricator.services.mozilla.com/D244285
6c3d2c6d8e