Parse async fn header.

This is gated on edition 2018 & the `async_await` feature gate.

The parser will accept `async fn` and `async unsafe fn` as fn
items. Along the same lines as `const fn`, only `async unsafe fn`
is permitted, not `unsafe async fn`.The parser will not accept
`async` functions as trait methods.

To do a little code clean up, four fields of the function type
struct have been merged into the new `FnHeader` struct: constness,
asyncness, unsafety, and ABI.

Also, a small bug in HIR printing is fixed: it previously printed
`const unsafe fn` as `unsafe const fn`, which is grammatically
incorrect.

1 files changed, 5 insertions, 5 deletions

diff --git a/src/libsyntax_ext/deriving/generic/mod.rs b/src/libsyntax_ext/deriving/generic/mod.rs
index 672726d1475..3ea0eb8bbd8 100644
--- a/src/libsyntax_ext/deriving/generic/mod.rs
+++ b/src/libsyntax_ext/deriving/generic/mod.rs
@@ -197,7 +197,7 @@ use syntax::ast::{VariantData, GenericParamKind, GenericArg};
 use syntax::attr;
 use syntax::ext::base::{Annotatable, ExtCtxt};
 use syntax::ext::build::AstBuilder;
-use syntax::codemap::{self, dummy_spanned, respan};
+use syntax::codemap::{self, respan};
 use syntax::util::move_map::MoveMap;
 use syntax::ptr::P;
 use syntax::symbol::{Symbol, keywords};
@@ -971,10 +971,10 @@ impl<'a> MethodDef<'a> {
             defaultness: ast::Defaultness::Final,
             ident: method_ident,
             node: ast::ImplItemKind::Method(ast::MethodSig {
-                                                abi,
-                                                unsafety,
-                                                constness:
-                                                    dummy_spanned(ast::Constness::NotConst),
+                                                header: ast::FnHeader {
+                                                    unsafety, abi,
+                                                    ..ast::FnHeader::default()
+                                                },
                                                 decl: fn_decl,
                                             },
                                             body_block),