Function instance_flags 

pub fn instance_flags(flags: InstanceFlags, env: Option<&str>) -> InstanceFlags

wgpu’s instance flags for every instance an app creates, from flags (wgpu’s defaults with its environment variables applied) without VALIDATION_INDIRECT_CALL, unless WGPU_VALIDATION_INDIRECT_CALL asks for it (any value but 0). That validation builds an internal compute pipeline when each device is created; Intel Macs’ Metal compiler fails on it (“Compiler encountered an internal error”), the device is lost and the window never opens (#250). It only guards indirect draws and dispatches, which the apps do not issue.