Constant block_sys::BLOCK_USE_STRET

pub const BLOCK_USE_STRET: block_flags = 1 << 29; // 536_870_912i32

Block function uses a calling convention that returns a structure via a pointer passed in by the caller.

match (BLOCK_USE_STRET, BLOCK_HAS_SIGNATURE) { (false, false) => 10.6.ABI, no signature field available (true, false) => 10.6.ABI, no signature field available (false, true) => ABI.2010.3.16, regular calling convention, presence of signature field (true, true) => ABI.2010.3.16, stret calling convention, presence of signature field, }

See https://clang.llvm.org/docs/Block-ABI-Apple.html#high-level