diff --git a/src/librustc/hir/intravisit.rs b/src/librustc/hir/intravisit.rs
index 920635d838738..72de8ccd952d3 100644
--- a/src/librustc/hir/intravisit.rs
+++ b/src/librustc/hir/intravisit.rs
@@ -481,13 +481,13 @@ pub fn walk_item<'v, V: Visitor<'v>>(visitor: &mut V, item: &'v Item) {
             visitor.visit_ty(typ);
             visitor.visit_nested_body(body);
         }
-        ItemKind::Fn(ref declaration, header, ref generics, body_id) => {
+        ItemKind::Fn(ref sig, ref generics, body_id) => {
             visitor.visit_fn(FnKind::ItemFn(item.ident,
                                             generics,
-                                            header,
+                                            sig.header,
                                             &item.vis,
                                             &item.attrs),
-                             declaration,
+                             &sig.decl,
                              body_id,
                              item.span,
                              item.hir_id)
diff --git a/src/librustc/hir/lowering/item.rs b/src/librustc/hir/lowering/item.rs
index 5fe463d783f4b..5bc9fcb12f178 100644
--- a/src/librustc/hir/lowering/item.rs
+++ b/src/librustc/hir/lowering/item.rs
@@ -317,7 +317,7 @@ impl LoweringContext<'_> {
                     // declaration (decl), not the return types.
                     let body_id = this.lower_maybe_async_body(&decl, header.asyncness.node, body);
 
-                    let (generics, fn_decl) = this.add_in_band_defs(
+                    let (generics, decl) = this.add_in_band_defs(
                         generics,
                         fn_def_id,
                         AnonymousLifetimeMode::PassThrough,
@@ -328,13 +328,8 @@ impl LoweringContext<'_> {
                             header.asyncness.node.opt_return_id()
                         ),
                     );
-
-                    hir::ItemKind::Fn(
-                        fn_decl,
-                        this.lower_fn_header(header),
-                        generics,
-                        body_id,
-                    )
+                    let sig = hir::MethodSig { decl, header: this.lower_fn_header(header) };
+                    hir::ItemKind::Fn(sig, generics, body_id)
                 })
             }
             ItemKind::Mod(ref m) => hir::ItemKind::Mod(self.lower_mod(m)),
diff --git a/src/librustc/hir/map/blocks.rs b/src/librustc/hir/map/blocks.rs
index f670d5abe85e4..b2f4a015711db 100644
--- a/src/librustc/hir/map/blocks.rs
+++ b/src/librustc/hir/map/blocks.rs
@@ -219,16 +219,16 @@ impl<'a> FnLikeNode<'a> {
     {
         match self.node {
             map::Node::Item(i) => match i.kind {
-                ast::ItemKind::Fn(ref decl, header, ref generics, block) =>
+                ast::ItemKind::Fn(ref sig, ref generics, block) =>
                     item_fn(ItemFnParts {
                         id: i.hir_id,
                         ident: i.ident,
-                        decl: &decl,
+                        decl: &sig.decl,
                         body: block,
                         vis: &i.vis,
                         span: i.span,
                         attrs: &i.attrs,
-                        header,
+                        header: sig.header,
                         generics,
                     }),
                 _ => bug!("item FnLikeNode that is not fn-like"),
diff --git a/src/librustc/hir/map/mod.rs b/src/librustc/hir/map/mod.rs
index acadd77cc36c0..d7b1676c1d4d3 100644
--- a/src/librustc/hir/map/mod.rs
+++ b/src/librustc/hir/map/mod.rs
@@ -49,21 +49,21 @@ impl<'hir> Entry<'hir> {
         match self.node {
             Node::Item(ref item) => {
                 match item.kind {
-                    ItemKind::Fn(ref fn_decl, _, _, _) => Some(fn_decl),
+                    ItemKind::Fn(ref sig, _, _) => Some(&sig.decl),
                     _ => None,
                 }
             }
 
             Node::TraitItem(ref item) => {
                 match item.kind {
-                    TraitItemKind::Method(ref method_sig, _) => Some(&method_sig.decl),
+                    TraitItemKind::Method(ref sig, _) => Some(&sig.decl),
                     _ => None
                 }
             }
 
             Node::ImplItem(ref item) => {
                 match item.kind {
-                    ImplItemKind::Method(ref method_sig, _) => Some(&method_sig.decl),
+                    ImplItemKind::Method(ref sig, _) => Some(&sig.decl),
                     _ => None,
                 }
             }
@@ -85,7 +85,7 @@ impl<'hir> Entry<'hir> {
                 match item.kind {
                     ItemKind::Const(_, body) |
                     ItemKind::Static(.., body) |
-                    ItemKind::Fn(_, _, _, body) => Some(body),
+                    ItemKind::Fn(.., body) => Some(body),
                     _ => None,
                 }
             }
@@ -605,7 +605,7 @@ impl<'hir> Map<'hir> {
                 Node::TraitItem(ref trait_item) => Some(&trait_item.generics),
                 Node::Item(ref item) => {
                     match item.kind {
-                        ItemKind::Fn(_, _, ref generics, _) |
+                        ItemKind::Fn(_, ref generics, _) |
                         ItemKind::TyAlias(_, ref generics) |
                         ItemKind::Enum(_, ref generics) |
                         ItemKind::Struct(_, ref generics) |
@@ -702,9 +702,9 @@ impl<'hir> Map<'hir> {
                 ..
             }) => true,
             Node::Item(&Item {
-                kind: ItemKind::Fn(_, header, ..),
+                kind: ItemKind::Fn(ref sig, ..),
                 ..
-            }) => header.constness == Constness::Const,
+            }) => sig.header.constness == Constness::Const,
             _ => false,
         }
     }
diff --git a/src/librustc/hir/mod.rs b/src/librustc/hir/mod.rs
index d409ca6f3c5f5..93503c1509448 100644
--- a/src/librustc/hir/mod.rs
+++ b/src/librustc/hir/mod.rs
@@ -2534,7 +2534,7 @@ pub enum ItemKind {
     /// A `const` item.
     Const(P<Ty>, BodyId),
     /// A function declaration.
-    Fn(P<FnDecl>, FnHeader, Generics, BodyId),
+    Fn(MethodSig, Generics, BodyId),
     /// A module.
     Mod(Mod),
     /// An external module, e.g. `extern { .. }`.
@@ -2599,7 +2599,7 @@ impl ItemKind {
 
     pub fn generics(&self) -> Option<&Generics> {
         Some(match *self {
-            ItemKind::Fn(_, _, ref generics, _) |
+            ItemKind::Fn(_, ref generics, _) |
             ItemKind::TyAlias(_, ref generics) |
             ItemKind::OpaqueTy(OpaqueTy { ref generics, impl_trait_fn: None, .. }) |
             ItemKind::Enum(_, ref generics) |
diff --git a/src/librustc/hir/print.rs b/src/librustc/hir/print.rs
index a25c111b59871..69d2a9ad2810d 100644
--- a/src/librustc/hir/print.rs
+++ b/src/librustc/hir/print.rs
@@ -533,10 +533,10 @@ impl<'a> State<'a> {
                 self.s.word(";");
                 self.end(); // end the outer cbox
             }
-            hir::ItemKind::Fn(ref decl, header, ref param_names, body) => {
+            hir::ItemKind::Fn(ref sig, ref param_names, body) => {
                 self.head("");
-                self.print_fn(decl,
-                              header,
+                self.print_fn(&sig.decl,
+                              sig.header,
                               Some(item.ident.name),
                               param_names,
                               &item.vis,
diff --git a/src/librustc/infer/error_reporting/nice_region_error/find_anon_type.rs b/src/librustc/infer/error_reporting/nice_region_error/find_anon_type.rs
index f4751e591bf3c..db5557204e4da 100644
--- a/src/librustc/infer/error_reporting/nice_region_error/find_anon_type.rs
+++ b/src/librustc/infer/error_reporting/nice_region_error/find_anon_type.rs
@@ -31,10 +31,10 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
             if let Some(hir_id) = self.tcx().hir().as_local_hir_id(def_id) {
                 let fndecl = match self.tcx().hir().get(hir_id) {
                     Node::Item(&hir::Item {
-                        kind: hir::ItemKind::Fn(ref fndecl, ..),
+                        kind: hir::ItemKind::Fn(ref m, ..),
                         ..
-                    }) => &fndecl,
-                    Node::TraitItem(&hir::TraitItem {
+                    })
+                    | Node::TraitItem(&hir::TraitItem {
                         kind: hir::TraitItemKind::Method(ref m, ..),
                         ..
                     })
diff --git a/src/librustc/middle/reachable.rs b/src/librustc/middle/reachable.rs
index 8be64bf64b5e9..f77f5a72e60ce 100644
--- a/src/librustc/middle/reachable.rs
+++ b/src/librustc/middle/reachable.rs
@@ -33,7 +33,7 @@ fn item_might_be_inlined(tcx: TyCtxt<'tcx>, item: &hir::Item, attrs: CodegenFnAt
     }
 
     match item.kind {
-        hir::ItemKind::Fn(_, header, ..) if header.is_const() => {
+        hir::ItemKind::Fn(ref sig, ..) if sig.header.is_const() => {
             return true;
         }
         hir::ItemKind::Impl(..) |
@@ -225,8 +225,8 @@ impl<'a, 'tcx> ReachableContext<'a, 'tcx> {
             // If we are building an executable, only explicitly extern
             // types need to be exported.
             if let Node::Item(item) = *node {
-                let reachable = if let hir::ItemKind::Fn(_, header, ..) = item.kind {
-                    header.abi != Abi::Rust
+                let reachable = if let hir::ItemKind::Fn(ref sig, ..) = item.kind {
+                    sig.header.abi != Abi::Rust
                 } else {
                     false
                 };
diff --git a/src/librustc/middle/resolve_lifetime.rs b/src/librustc/middle/resolve_lifetime.rs
index 488d6332f7e39..f37d9b2827be0 100644
--- a/src/librustc/middle/resolve_lifetime.rs
+++ b/src/librustc/middle/resolve_lifetime.rs
@@ -460,8 +460,8 @@ impl<'a, 'tcx> Visitor<'tcx> for LifetimeContext<'a, 'tcx> {
 
     fn visit_item(&mut self, item: &'tcx hir::Item) {
         match item.kind {
-            hir::ItemKind::Fn(ref decl, _, ref generics, _) => {
-                self.visit_early_late(None, decl, generics, |this| {
+            hir::ItemKind::Fn(ref sig, ref generics, _) => {
+                self.visit_early_late(None, &sig.decl, generics, |this| {
                     intravisit::walk_item(this, item);
                 });
             }
@@ -1524,8 +1524,8 @@ impl<'a, 'tcx> LifetimeContext<'a, 'tcx> {
             {
                 match parent {
                     Node::Item(item) => {
-                        if let hir::ItemKind::Fn(decl, _, _, _) = &item.kind {
-                            find_arg_use_span(&decl.inputs);
+                        if let hir::ItemKind::Fn(sig, _, _) = &item.kind {
+                            find_arg_use_span(&sig.decl.inputs);
                         }
                     },
                     Node::ImplItem(impl_item) => {
diff --git a/src/librustc/traits/error_reporting.rs b/src/librustc/traits/error_reporting.rs
index fe18a14d89058..54c0103422173 100644
--- a/src/librustc/traits/error_reporting.rs
+++ b/src/librustc/traits/error_reporting.rs
@@ -383,9 +383,9 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         let hir = &self.tcx.hir();
         let node = hir.find(hir_id)?;
         if let hir::Node::Item(
-            hir::Item{kind: hir::ItemKind::Fn(_ ,fn_header ,_ , body_id), .. }) = &node {
+            hir::Item{kind: hir::ItemKind::Fn(sig, _, body_id), .. }) = &node {
             self.describe_generator(*body_id).or_else(||
-                Some(if let hir::FnHeader{ asyncness: hir::IsAsync::Async, .. } = fn_header {
+                Some(if let hir::FnHeader{ asyncness: hir::IsAsync::Async, .. } = sig.header {
                     "an async function"
                 } else {
                     "a function"
@@ -1081,7 +1081,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                 }
 
                 hir::Node::Item(hir::Item {
-                    kind: hir::ItemKind::Fn(_, _, generics, _), ..
+                    kind: hir::ItemKind::Fn(_, generics, _), ..
                 }) |
                 hir::Node::TraitItem(hir::TraitItem {
                     generics,
@@ -1112,7 +1112,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                     kind: hir::ItemKind::Impl(_, _, _, generics, ..), span, ..
                 }) |
                 hir::Node::Item(hir::Item {
-                    kind: hir::ItemKind::Fn(_, _, generics, _), span, ..
+                    kind: hir::ItemKind::Fn(_, generics, _), span, ..
                 }) |
                 hir::Node::Item(hir::Item {
                     kind: hir::ItemKind::TyAlias(_, generics), span, ..
@@ -1436,12 +1436,12 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         let parent_node = hir.get_parent_node(obligation.cause.body_id);
         let node = hir.find(parent_node);
         if let Some(hir::Node::Item(hir::Item {
-            kind: hir::ItemKind::Fn(decl, _, _, body_id),
+            kind: hir::ItemKind::Fn(sig, _, body_id),
             ..
         })) = node {
             let body = hir.body(*body_id);
             if let hir::ExprKind::Block(blk, _) = &body.value.kind {
-                if decl.output.span().overlaps(span) && blk.expr.is_none() &&
+                if sig.decl.output.span().overlaps(span) && blk.expr.is_none() &&
                     "()" == &trait_ref.self_ty().to_string()
                 {
                     // FIXME(estebank): When encountering a method with a trait
@@ -1493,20 +1493,20 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
             }
             Node::Item(&hir::Item {
                 span,
-                kind: hir::ItemKind::Fn(ref decl, ..),
+                kind: hir::ItemKind::Fn(ref sig, ..),
                 ..
             }) |
             Node::ImplItem(&hir::ImplItem {
                 span,
-                kind: hir::ImplItemKind::Method(hir::MethodSig { ref decl, .. }, _),
+                kind: hir::ImplItemKind::Method(ref sig, _),
                 ..
             }) |
             Node::TraitItem(&hir::TraitItem {
                 span,
-                kind: hir::TraitItemKind::Method(hir::MethodSig { ref decl, .. }, _),
+                kind: hir::TraitItemKind::Method(ref sig, _),
                 ..
             }) => {
-                (self.tcx.sess.source_map().def_span(span), decl.inputs.iter()
+                (self.tcx.sess.source_map().def_span(span), sig.decl.inputs.iter()
                         .map(|arg| match arg.clone().kind {
                     hir::TyKind::Tup(ref tys) => ArgKind::Tuple(
                         Some(arg.span),
@@ -2040,11 +2040,11 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
             .and_then(|parent_did| self.tcx.hir().get_if_local(parent_did));
         debug!("note_obligation_cause_for_async_await: parent_node={:?}", parent_node);
         if let Some(hir::Node::Item(hir::Item {
-            kind: hir::ItemKind::Fn(_, header, _, _),
+            kind: hir::ItemKind::Fn(sig, _, _),
             ..
         })) = parent_node {
-            debug!("note_obligation_cause_for_async_await: header={:?}", header);
-            if header.asyncness != hir::IsAsync::Async {
+            debug!("note_obligation_cause_for_async_await: header={:?}", sig.header);
+            if sig.header.asyncness != hir::IsAsync::Async {
                 return false;
             }
         }
diff --git a/src/librustc_metadata/rmeta/encoder.rs b/src/librustc_metadata/rmeta/encoder.rs
index afc81649e3719..c6677ea3534d0 100644
--- a/src/librustc_metadata/rmeta/encoder.rs
+++ b/src/librustc_metadata/rmeta/encoder.rs
@@ -1095,10 +1095,10 @@ impl EncodeContext<'tcx> {
                     self.encode_rendered_const_for_body(body_id)
                 )
             }
-            hir::ItemKind::Fn(_, header, .., body) => {
+            hir::ItemKind::Fn(ref sig, .., body) => {
                 let data = FnData {
-                    asyncness: header.asyncness,
-                    constness: header.constness,
+                    asyncness: sig.header.asyncness,
+                    constness: sig.header.constness,
                     param_names: self.encode_fn_param_names_for_body(body),
                 };
 
@@ -1284,14 +1284,14 @@ impl EncodeContext<'tcx> {
 
         let mir = match item.kind {
             hir::ItemKind::Static(..) | hir::ItemKind::Const(..) => true,
-            hir::ItemKind::Fn(_, header, ..) => {
+            hir::ItemKind::Fn(ref sig, ..) => {
                 let generics = tcx.generics_of(def_id);
                 let needs_inline =
                     (generics.requires_monomorphization(tcx) ||
                         tcx.codegen_fn_attrs(def_id).requests_inline()) &&
                         !self.metadata_output_only();
                 let always_encode_mir = self.tcx.sess.opts.debugging_opts.always_encode_mir;
-                needs_inline || header.constness == hir::Constness::Const || always_encode_mir
+                needs_inline || sig.header.constness == hir::Constness::Const || always_encode_mir
             }
             _ => false,
         };
diff --git a/src/librustc_mir/build/mod.rs b/src/librustc_mir/build/mod.rs
index ffb70180bbb4b..59301619b4bdd 100644
--- a/src/librustc_mir/build/mod.rs
+++ b/src/librustc_mir/build/mod.rs
@@ -30,7 +30,12 @@ pub fn mir_build(tcx: TyCtxt<'_>, def_id: DefId) -> Body<'_> {
     // Figure out what primary body this item has.
     let (body_id, return_ty_span) = match tcx.hir().get(id) {
         Node::Expr(hir::Expr { kind: hir::ExprKind::Closure(_, decl, body_id, _, _), .. })
-        | Node::Item(hir::Item { kind: hir::ItemKind::Fn(decl, _, _, body_id), .. })
+        | Node::Item(
+            hir::Item {
+                kind: hir::ItemKind::Fn(hir::MethodSig { decl, .. }, _, body_id),
+                ..
+            }
+        )
         | Node::ImplItem(
             hir::ImplItem {
                 kind: hir::ImplItemKind::Method(hir::MethodSig { decl, .. }, body_id),
diff --git a/src/librustc_mir/transform/check_unsafety.rs b/src/librustc_mir/transform/check_unsafety.rs
index 7d5507168587b..4b57cb75cea48 100644
--- a/src/librustc_mir/transform/check_unsafety.rs
+++ b/src/librustc_mir/transform/check_unsafety.rs
@@ -576,10 +576,10 @@ fn is_enclosed(
         if used_unsafe.contains(&parent_id) {
             Some(("block".to_string(), parent_id))
         } else if let Some(Node::Item(&hir::Item {
-            kind: hir::ItemKind::Fn(_, header, _, _),
+            kind: hir::ItemKind::Fn(ref sig, _, _),
             ..
         })) = tcx.hir().find(parent_id) {
-            match header.unsafety {
+            match sig.header.unsafety {
                 hir::Unsafety::Unsafe => Some(("fn".to_string(), parent_id)),
                 hir::Unsafety::Normal => None,
             }
diff --git a/src/librustc_typeck/check/mod.rs b/src/librustc_typeck/check/mod.rs
index fe2c7a200d202..39a7996df0cdc 100644
--- a/src/librustc_typeck/check/mod.rs
+++ b/src/librustc_typeck/check/mod.rs
@@ -815,8 +815,8 @@ fn primary_body_of(
                 hir::ItemKind::Const(ref ty, body) |
                 hir::ItemKind::Static(ref ty, _, body) =>
                     Some((body, Some(ty), None, None)),
-                hir::ItemKind::Fn(ref decl, ref header, .., body) =>
-                    Some((body, None, Some(header), Some(decl))),
+                hir::ItemKind::Fn(ref sig, .., body) =>
+                    Some((body, None, Some(&sig.header), Some(&sig.decl))),
                 _ =>
                     None,
             }
@@ -1297,7 +1297,7 @@ fn check_fn<'a, 'tcx>(
                     }
 
                     if let Node::Item(item) = fcx.tcx.hir().get(fn_id) {
-                        if let ItemKind::Fn(_, _, ref generics, _) = item.kind {
+                        if let ItemKind::Fn(_, ref generics, _) = item.kind {
                             if !generics.params.is_empty() {
                                 fcx.tcx.sess.span_err(
                                     span,
@@ -1345,7 +1345,7 @@ fn check_fn<'a, 'tcx>(
                     }
 
                     if let Node::Item(item) = fcx.tcx.hir().get(fn_id) {
-                        if let ItemKind::Fn(_, _, ref generics, _) = item.kind {
+                        if let ItemKind::Fn(_, ref generics, _) = item.kind {
                             if !generics.params.is_empty() {
                                 fcx.tcx.sess.span_err(
                                     span,
@@ -4278,7 +4278,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         let node = self.tcx.hir().get(self.tcx.hir().get_parent_item(id));
         match node {
             Node::Item(&hir::Item {
-                kind: hir::ItemKind::Fn(_, _, _, body_id), ..
+                kind: hir::ItemKind::Fn(_, _, body_id), ..
             }) |
             Node::ImplItem(&hir::ImplItem {
                 kind: hir::ImplItemKind::Method(_, body_id), ..
@@ -4303,23 +4303,19 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     fn get_node_fn_decl(&self, node: Node<'tcx>) -> Option<(&'tcx hir::FnDecl, ast::Ident, bool)> {
         match node {
             Node::Item(&hir::Item {
-                ident, kind: hir::ItemKind::Fn(ref decl, ..), ..
+                ident, kind: hir::ItemKind::Fn(ref sig, ..), ..
             }) => {
                 // This is less than ideal, it will not suggest a return type span on any
                 // method called `main`, regardless of whether it is actually the entry point,
                 // but it will still present it as the reason for the expected type.
-                Some((decl, ident, ident.name != sym::main))
+                Some((&sig.decl, ident, ident.name != sym::main))
             }
             Node::TraitItem(&hir::TraitItem {
-                ident, kind: hir::TraitItemKind::Method(hir::MethodSig {
-                    ref decl, ..
-                }, ..), ..
-            }) => Some((decl, ident, true)),
+                ident, kind: hir::TraitItemKind::Method(ref sig, ..), ..
+            }) => Some((&sig.decl, ident, true)),
             Node::ImplItem(&hir::ImplItem {
-                ident, kind: hir::ImplItemKind::Method(hir::MethodSig {
-                    ref decl, ..
-                }, ..), ..
-            }) => Some((decl, ident, false)),
+                ident, kind: hir::ImplItemKind::Method(ref sig, ..), ..
+            }) => Some((&sig.decl, ident, false)),
             _ => None,
         }
     }
diff --git a/src/librustc_typeck/collect.rs b/src/librustc_typeck/collect.rs
index ef84f1cb20f51..68fd29d04e33f 100644
--- a/src/librustc_typeck/collect.rs
+++ b/src/librustc_typeck/collect.rs
@@ -885,8 +885,8 @@ fn has_late_bound_regions<'tcx>(tcx: TyCtxt<'tcx>, node: Node<'tcx>) -> Option<S
             _ => None,
         },
         Node::Item(item) => match item.kind {
-            hir::ItemKind::Fn(ref fn_decl, .., ref generics, _) => {
-                has_late_bound_regions(tcx, generics, fn_decl)
+            hir::ItemKind::Fn(ref sig, .., ref generics, _) => {
+                has_late_bound_regions(tcx, generics, &sig.decl)
             }
             _ => None,
         },
@@ -1779,17 +1779,17 @@ fn fn_sig(tcx: TyCtxt<'_>, def_id: DefId) -> ty::PolyFnSig<'_> {
 
     match tcx.hir().get(hir_id) {
         TraitItem(hir::TraitItem {
-            kind: TraitItemKind::Method(MethodSig { header, decl }, TraitMethod::Provided(_)),
+            kind: TraitItemKind::Method(sig, TraitMethod::Provided(_)),
             ..
         })
         | ImplItem(hir::ImplItem {
-            kind: ImplItemKind::Method(MethodSig { header, decl }, _),
+            kind: ImplItemKind::Method(sig, _),
             ..
         })
         | Item(hir::Item {
-            kind: ItemKind::Fn(decl, header, _, _),
+            kind: ItemKind::Fn(sig, _, _),
             ..
-        }) => match get_infer_ret_ty(&decl.output) {
+        }) => match get_infer_ret_ty(&sig.decl.output) {
             Some(ty) => {
                 let fn_sig = tcx.typeck_tables_of(def_id).liberated_fn_sigs()[hir_id];
                 let mut diag = bad_placeholder_type(tcx, ty.span);
@@ -1805,7 +1805,7 @@ fn fn_sig(tcx: TyCtxt<'_>, def_id: DefId) -> ty::PolyFnSig<'_> {
                 diag.emit();
                 ty::Binder::bind(fn_sig)
             },
-            None => AstConv::ty_of_fn(&icx, header.unsafety, header.abi, decl)
+            None => AstConv::ty_of_fn(&icx, sig.header.unsafety, sig.header.abi, &sig.decl)
         },
 
         TraitItem(hir::TraitItem {
diff --git a/src/librustdoc/visit_ast.rs b/src/librustdoc/visit_ast.rs
index 5a83569f02a5c..aea9b7c38efba 100644
--- a/src/librustdoc/visit_ast.rs
+++ b/src/librustdoc/visit_ast.rs
@@ -438,8 +438,8 @@ impl<'a, 'tcx> RustdocVisitor<'a, 'tcx> {
                 om.structs.push(self.visit_variant_data(item, ident.name, sd, gen)),
             hir::ItemKind::Union(ref sd, ref gen) =>
                 om.unions.push(self.visit_union_data(item, ident.name, sd, gen)),
-            hir::ItemKind::Fn(ref fd, header, ref gen, body) =>
-                self.visit_fn(om, item, ident.name, &**fd, header, gen, body),
+            hir::ItemKind::Fn(ref sig, ref gen, body) =>
+                self.visit_fn(om, item, ident.name, &sig.decl, sig.header, gen, body),
             hir::ItemKind::TyAlias(ref ty, ref gen) => {
                 let t = Typedef {
                     ty,