error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
  --> tests/ui-nightly/transmute-size-increase.rs:19:29
   |
19 | const INCREASE_SIZE: AU16 = transmute!(0u8);
   |                             ^^^^^^^^^^^^^^^
   |
   = note: source type: `u8` (8 bits)
   = note: target type: `AU16` (16 bits)
   = note: this error originates in the macro `transmute` (in Nightly builds, run with -Z macro-backtrace for more info)