Auto merge of #51580 - cramertj:async-await, r=eddyb

async/await

This PR implements `async`/`await` syntax for `async fn` in Rust 2015 and `async` closures and `async` blocks in Rust 2018 (tracking issue: https://github.com/rust-lang/rust/issues/50547). Limitations: non-`move` async closures with arguments are currently not supported, nor are `async fn` with multiple different input lifetimes. These limitations are not fundamental and will be removed in the future, however I'd like to go ahead and get this PR merged so we can start experimenting with this in combination with futures 0.3.

Based on https://github.com/rust-lang/rust/pull/51414.
cc @petrochenkov for parsing changes.
r? @eddyb

1 files changed, 2 insertions, 0 deletions

diff --git a/src/libsyntax/util/parser.rs b/src/libsyntax/util/parser.rs
index 51b535275d6..15d910b33b0 100644
--- a/src/libsyntax/util/parser.rs
+++ b/src/libsyntax/util/parser.rs
@@ -277,6 +277,7 @@ pub enum ExprPrecedence {
     Block,
     Catch,
     Struct,
+    Async,
 }
 
 impl PartialOrd for ExprPrecedence {
@@ -346,6 +347,7 @@ impl ExprPrecedence {
             ExprPrecedence::Match |
             ExprPrecedence::Block |
             ExprPrecedence::Catch |
+            ExprPrecedence::Async |
             ExprPrecedence::Struct => PREC_PAREN,
         }
     }