diff --git a/clippy_lints/src/attrs.rs b/clippy_lints/src/attrs.rs
index 06df8504d..5c881adca 100644
--- a/clippy_lints/src/attrs.rs
+++ b/clippy_lints/src/attrs.rs
@@ -355,7 +355,7 @@ fn check_clippy_lint_names(cx: &LateContext<'_, '_>, items: &[NestedMetaItem]) {
 }
 
 fn is_relevant_item(cx: &LateContext<'_, '_>, item: &Item) -> bool {
-    if let ItemKind::Fn(_, _, _, eid) = item.kind {
+    if let ItemKind::Fn(_, _, eid) = item.kind {
         is_relevant_expr(cx, cx.tcx.body_tables(eid), &cx.tcx.hir().body(eid).value)
     } else {
         true
diff --git a/clippy_lints/src/doc.rs b/clippy_lints/src/doc.rs
index aca4d1767..e014d1912 100644
--- a/clippy_lints/src/doc.rs
+++ b/clippy_lints/src/doc.rs
@@ -126,8 +126,8 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for DocMarkdown {
         }
         // no safety header
         match item.kind {
-            hir::ItemKind::Fn(_, ref header, ..) => {
-                if cx.access_levels.is_exported(item.hir_id) && header.unsafety == hir::Unsafety::Unsafe {
+            hir::ItemKind::Fn(ref sig, ..) => {
+                if cx.access_levels.is_exported(item.hir_id) && sig.header.unsafety == hir::Unsafety::Unsafe {
                     span_lint(
                         cx,
                         MISSING_SAFETY_DOC,
diff --git a/clippy_lints/src/functions.rs b/clippy_lints/src/functions.rs
index 59a16c36d..8c3306f6d 100644
--- a/clippy_lints/src/functions.rs
+++ b/clippy_lints/src/functions.rs
@@ -208,7 +208,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Functions {
             match kind {
                 hir::intravisit::FnKind::Method(
                     _,
-                    &hir::MethodSig {
+                    &hir::FnSig {
                         header: hir::FnHeader { abi: Abi::Rust, .. },
                         ..
                     },
@@ -228,20 +228,20 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Functions {
 
     fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx hir::Item) {
         let attr = must_use_attr(&item.attrs);
-        if let hir::ItemKind::Fn(ref decl, ref _header, ref _generics, ref body_id) = item.kind {
+        if let hir::ItemKind::Fn(ref sig, ref _generics, ref body_id) = item.kind {
             if let Some(attr) = attr {
-                let fn_header_span = item.span.with_hi(decl.output.span().hi());
-                check_needless_must_use(cx, decl, item.hir_id, item.span, fn_header_span, attr);
+                let fn_header_span = item.span.with_hi(sig.decl.output.span().hi());
+                check_needless_must_use(cx, &sig.decl, item.hir_id, item.span, fn_header_span, attr);
                 return;
             }
             if cx.access_levels.is_exported(item.hir_id) && !is_proc_macro(&item.attrs) {
                 check_must_use_candidate(
                     cx,
-                    decl,
+                    &sig.decl,
                     cx.tcx.hir().body(*body_id),
                     item.span,
                     item.hir_id,
-                    item.span.with_hi(decl.output.span().hi()),
+                    item.span.with_hi(sig.decl.output.span().hi()),
                     "this function could have a `#[must_use]` attribute",
                 );
             }
diff --git a/clippy_lints/src/lifetimes.rs b/clippy_lints/src/lifetimes.rs
index be1e65fc1..fad54c3de 100644
--- a/clippy_lints/src/lifetimes.rs
+++ b/clippy_lints/src/lifetimes.rs
@@ -59,8 +59,8 @@ declare_lint_pass!(Lifetimes => [NEEDLESS_LIFETIMES, EXTRA_UNUSED_LIFETIMES]);
 
 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Lifetimes {
     fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx Item) {
-        if let ItemKind::Fn(ref decl, _, ref generics, id) = item.kind {
-            check_fn_inner(cx, decl, Some(id), generics, item.span, true);
+        if let ItemKind::Fn(ref sig, ref generics, id) = item.kind {
+            check_fn_inner(cx, &sig.decl, Some(id), generics, item.span, true);
         }
     }
 
diff --git a/clippy_lints/src/non_expressive_names.rs b/clippy_lints/src/non_expressive_names.rs
index 12df93256..8ac31743a 100644
--- a/clippy_lints/src/non_expressive_names.rs
+++ b/clippy_lints/src/non_expressive_names.rs
@@ -352,8 +352,8 @@ impl<'a, 'tcx> Visitor<'tcx> for SimilarNamesLocalVisitor<'a, 'tcx> {
 
 impl EarlyLintPass for NonExpressiveNames {
     fn check_item(&mut self, cx: &EarlyContext<'_>, item: &Item) {
-        if let ItemKind::Fn(ref decl, _, _, ref blk) = item.kind {
-            do_check(self, cx, &item.attrs, decl, blk);
+        if let ItemKind::Fn(ref sig, _, ref blk) = item.kind {
+            do_check(self, cx, &item.attrs, &sig.decl, blk);
         }
     }
 
diff --git a/clippy_lints/src/ptr.rs b/clippy_lints/src/ptr.rs
index 8b9e39e34..55662a1ad 100644
--- a/clippy_lints/src/ptr.rs
+++ b/clippy_lints/src/ptr.rs
@@ -101,8 +101,8 @@ declare_lint_pass!(Ptr => [PTR_ARG, CMP_NULL, MUT_FROM_REF]);
 
 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Ptr {
     fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx Item) {
-        if let ItemKind::Fn(ref decl, _, _, body_id) = item.kind {
-            check_fn(cx, decl, item.hir_id, Some(body_id));
+        if let ItemKind::Fn(ref sig, _, body_id) = item.kind {
+            check_fn(cx, &sig.decl, item.hir_id, Some(body_id));
         }
     }
 
diff --git a/clippy_lints/src/types.rs b/clippy_lints/src/types.rs
index 62da724ff..c303445f7 100644
--- a/clippy_lints/src/types.rs
+++ b/clippy_lints/src/types.rs
@@ -1408,7 +1408,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for TypeComplexity {
     fn check_trait_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx TraitItem) {
         match item.kind {
             TraitItemKind::Const(ref ty, _) | TraitItemKind::Type(_, Some(ref ty)) => self.check_type(cx, ty),
-            TraitItemKind::Method(MethodSig { ref decl, .. }, TraitMethod::Required(_)) => self.check_fndecl(cx, decl),
+            TraitItemKind::Method(FnSig { ref decl, .. }, TraitMethod::Required(_)) => self.check_fndecl(cx, decl),
             // methods with default impl are covered by check_fn
             _ => (),
         }
@@ -2118,10 +2118,10 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ImplicitHasher {
                     );
                 }
             },
-            ItemKind::Fn(ref decl, .., ref generics, body_id) => {
+            ItemKind::Fn(ref sig, ref generics, body_id) => {
                 let body = cx.tcx.hir().body(body_id);
 
-                for ty in &decl.inputs {
+                for ty in &sig.decl.inputs {
                     let mut vis = ImplicitHasherTypeVisitor::new(cx);
                     vis.visit_ty(ty);
 
diff --git a/clippy_lints/src/use_self.rs b/clippy_lints/src/use_self.rs
index 35e154aea..98a788954 100644
--- a/clippy_lints/src/use_self.rs
+++ b/clippy_lints/src/use_self.rs
@@ -193,7 +193,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UseSelf {
                     if let Some(impl_trait_ref) = impl_trait_ref {
                         for impl_item_ref in refs {
                             let impl_item = cx.tcx.hir().impl_item(impl_item_ref.id);
-                            if let ImplItemKind::Method(MethodSig{ decl: impl_decl, .. }, impl_body_id)
+                            if let ImplItemKind::Method(FnSig{ decl: impl_decl, .. }, impl_body_id)
                                     = &impl_item.kind {
                                 let item_type = cx.tcx.type_of(impl_def_id);
                                 check_trait_method_impl_decl(cx, item_type, impl_item, impl_decl, &impl_trait_ref);
diff --git a/clippy_lints/src/utils/mod.rs b/clippy_lints/src/utils/mod.rs
index bf46a9a8b..092606d56 100644
--- a/clippy_lints/src/utils/mod.rs
+++ b/clippy_lints/src/utils/mod.rs
@@ -87,9 +87,9 @@ pub fn in_constant(cx: &LateContext<'_, '_>, id: HirId) -> bool {
             ..
         }) => true,
         Node::Item(&Item {
-            kind: ItemKind::Fn(_, header, ..),
+            kind: ItemKind::Fn(ref sig, ..),
             ..
-        }) => header.constness == Constness::Const,
+        }) => sig.header.constness == Constness::Const,
         Node::ImplItem(&ImplItem {
             kind: ImplItemKind::Method(ref sig, _),
             ..
@@ -635,7 +635,7 @@ pub fn get_enclosing_block<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, hir_id: HirId)
         match node {
             Node::Block(block) => Some(block),
             Node::Item(&Item {
-                kind: ItemKind::Fn(_, _, _, eid),
+                kind: ItemKind::Fn(_, _, eid),
                 ..
             })
             | Node::ImplItem(&ImplItem {