From 35fb7455cac402452b5d4d1d4bb93cef50e51d94 Mon Sep 17 00:00:00 2001
From: Paul Lancaster <paul@lancasterzone.com>
Date: Sat, 10 Oct 2020 11:22:27 +0100
Subject: [PATCH] AsyncFunctionExpr parsing

---
 .../primary/async_function_expression.rs      | 51 +++++++++++++++++--
 .../syntax/parser/expression/primary/mod.rs   |  6 +--
 2 files changed, 49 insertions(+), 8 deletions(-)

diff --git a/boa/src/syntax/parser/expression/primary/async_function_expression.rs b/boa/src/syntax/parser/expression/primary/async_function_expression.rs
index 61f24e8412..d030f848d6 100644
--- a/boa/src/syntax/parser/expression/primary/async_function_expression.rs
+++ b/boa/src/syntax/parser/expression/primary/async_function_expression.rs
@@ -6,11 +6,15 @@
 //!
 //! [mdn]:
 //! [spec]:
-
 use crate::{
     syntax::{
-        ast::node::AsyncFunctionExpr,
-        parser::{Cursor, ParseError, TokenParser},
+        ast::{node::AsyncFunctionExpr, Keyword, Punctuator},
+        lexer::TokenKind,
+        parser::{
+            function::{FormalParameters, FunctionBody},
+            statement::BindingIdentifier,
+            AllowYield, Cursor, ParseError, TokenParser,
+        },
     },
     BoaProfiler,
 };
@@ -26,7 +30,21 @@ use std::io::Read;
 /// [mdn]:
 /// [spec]:
 #[derive(Debug, Clone, Copy)]
-pub(super) struct AsyncFunctionExpression;
+pub(super) struct AsyncFunctionExpression {
+    allow_yield: AllowYield,
+}
+
+impl AsyncFunctionExpression {
+    /// Creates a new `AsyncFunctionExpression` parser.
+    pub(super) fn new<Y>(allow_yield: Y) -> Self
+    where
+        Y: Into<AllowYield>,
+    {
+        Self {
+            allow_yield: allow_yield.into(),
+        }
+    }
+}
 
 impl<R> TokenParser<R> for AsyncFunctionExpression
 where
@@ -36,7 +54,30 @@ where
 
     fn parse(self, cursor: &mut Cursor<R>) -> Result<Self::Output, ParseError> {
         let _timer = BoaProfiler::global().start_event("AsyncFunctionExpression", "Parsing");
+        cursor.expect_no_skip_lineterminator(Keyword::Function, "async function expression")?;
+
+        let tok = cursor.peek(0)?;
+
+        let name = if let Some(token) = tok {
+            match token.kind() {
+                TokenKind::Punctuator(Punctuator::OpenParen) => None,
+                _ => Some(BindingIdentifier::new(self.allow_yield, true).parse(cursor)?),
+            }
+        } else {
+            return Err(ParseError::AbruptEnd);
+        };
+
+        cursor.expect(Punctuator::OpenParen, "function expression")?;
+
+        let params = FormalParameters::new(!self.allow_yield.0, true).parse(cursor)?;
+
+        cursor.expect(Punctuator::CloseParen, "function expression")?;
+        cursor.expect(Punctuator::OpenBlock, "function expression")?;
+
+        let body = FunctionBody::new(!self.allow_yield.0, true).parse(cursor)?;
+
+        cursor.expect(Punctuator::CloseBlock, "function expression")?;
 
-        unimplemented!("Async function expression parse");
+        Ok(AsyncFunctionExpr::new(name, params, body))
     }
 }
diff --git a/boa/src/syntax/parser/expression/primary/mod.rs b/boa/src/syntax/parser/expression/primary/mod.rs
index 9963df4b57..7f55346663 100644
--- a/boa/src/syntax/parser/expression/primary/mod.rs
+++ b/boa/src/syntax/parser/expression/primary/mod.rs
@@ -78,9 +78,9 @@ where
             TokenKind::Keyword(Keyword::Function) => {
                 FunctionExpression.parse(cursor).map(Node::from)
             }
-            TokenKind::Keyword(Keyword::Async) => {
-                AsyncFunctionExpression.parse(cursor).map(Node::from)
-            }
+            TokenKind::Keyword(Keyword::Async) => AsyncFunctionExpression::new(self.allow_yield)
+                .parse(cursor)
+                .map(Node::from),
             TokenKind::Punctuator(Punctuator::OpenParen) => {
                 cursor.set_goal(InputElement::RegExp);
                 let expr =