Add comment to AllocatorKind and AllocatorMethod

Author: bjorn3

compiler/rustc_ast/src/expand/allocator.rs

@@ -3,7 +3,9 @@ use rustc_span::{Symbol, sym};
 
 #[derive(Clone, Debug, Copy, Eq, PartialEq, HashStable_Generic)]
 pub enum AllocatorKind {
+ /// Use `#[global_allocator]` as global allocator.
  Global,
+ /// Use the default implementation in libstd as global allocator.
  Default,
 }
 
@@ -29,6 +31,7 @@ pub enum AllocatorTy {
  Usize,
 }
 
+/// A method that will be codegened in the allocator shim.
 #[derive(Copy, Clone)]
 pub struct AllocatorMethod {
  pub name: Symbol,