Format Async block and async fn

src/expr.rs

@@ -345,8 +345,27 @@ pub fn format_expr(
         }
         // FIXME(#2743)
         ast::ExprKind::ObsoleteInPlace(..) => unimplemented!(),
-        // FIXME(topecongiro) Format async block.
-        ast::ExprKind::Async(..) => None,
+        ast::ExprKind::Async(_capture_by, _node_id, ref block) => {
+            if let rw @ Some(_) =
+                rewrite_single_line_block(context, "async ", block, Some(&expr.attrs), None, shape)
+            {
+                rw
+            } else {
+                // 6 = `async `
+                let budget = shape.width.saturating_sub(6);
+                Some(format!(
+                    "{}{}",
+                    "async ",
+                    rewrite_block(
+                        block,
+                        Some(&expr.attrs),
+                        None,
+                        context,
+                        Shape::legacy(budget, shape.indent)
+                    )?
+                ))
+            }
+        }
     };
 
     expr_rw

src/items.rs

@@ -164,6 +164,7 @@ pub struct FnSig<'a> {
     decl: &'a ast::FnDecl,
     generics: &'a ast::Generics,
     abi: abi::Abi,
+    asyncness: ast::IsAsync,
     constness: ast::Constness,
     defaultness: ast::Defaultness,
     unsafety: ast::Unsafety,
@@ -180,6 +181,7 @@ impl<'a> FnSig<'a> {
             decl,
             generics,
             abi: abi::Abi::Rust,
+            asyncness: ast::IsAsync::NotAsync,
             constness: ast::Constness::NotConst,
             defaultness: ast::Defaultness::Final,
             unsafety: ast::Unsafety::Normal,
@@ -193,6 +195,7 @@ impl<'a> FnSig<'a> {
     ) -> FnSig<'a> {
         FnSig {
             unsafety: method_sig.header.unsafety,
+            asyncness: method_sig.header.asyncness,
             constness: method_sig.header.constness.node,
             defaultness: ast::Defaultness::Final,
             abi: method_sig.header.abi,
@@ -214,6 +217,7 @@ impl<'a> FnSig<'a> {
                 generics,
                 abi: fn_header.abi,
                 constness: fn_header.constness.node,
+                asyncness: fn_header.asyncness,
                 defaultness,
                 unsafety: fn_header.unsafety,
                 visibility: visibility.clone(),
@@ -235,6 +239,7 @@ impl<'a> FnSig<'a> {
         // Vis defaultness constness unsafety abi.
         result.push_str(&*format_visibility(context, &self.visibility));
         result.push_str(format_defaultness(self.defaultness));
+        result.push_str(format_asyncness(self.asyncness));
         result.push_str(format_constness(self.constness));
         result.push_str(format_unsafety(self.unsafety));
         result.push_str(&format_abi(

src/utils.rs

@@ -81,6 +81,14 @@ pub fn format_visibility(context: &RewriteContext, vis: &Visibility) -> Cow<'sta
     }
 }
 
+#[inline]
+pub fn format_asyncness(asyncness: ast::IsAsync) -> &'static str {
+    match asyncness {
+        ast::IsAsync::Async { .. } => "async ",
+        ast::IsAsync::NotAsync => "",
+    }
+}
+
 #[inline]
 pub fn format_constness(constness: ast::Constness) -> &'static str {
     match constness {

src/visitor.rs

@@ -253,7 +253,6 @@ impl<'b, 'a: 'b> FmtVisitor<'a> {
 
     // Note that this only gets called for function definitions. Required methods
     // on traits do not get handled here.
-    // FIXME(topecongiro) Format async fn (#2812).
     fn visit_fn(
         &mut self,
         fk: visit::FnKind,