syntax_data: {"ast_node_type":"other","tokens":[{"end":69,"kind":"keyword","start":0,"text":"//"}]}
source_snippet:     // this is understood as a special case elsewhere in the compiler
context_before:     // change its layout to that of `*mut ()`, a thin pointer, but keep the same type
context_after:     let unit_ptr_ty = Ty::new_mut_ptr(tcx, tcx.types.unit);