Rollup merge of #98705 - WaffleLapkin:closure_binder, r=cjgillot

Implement `for<>` lifetime binder for closures

This PR implements RFC 3216 ([TI](rust-lang/rust#97362)) and allows code like the following:

```rust
let _f = for<'a, 'b> |a: &'a A, b: &'b B| -> &'b C { b.c(a) };
//       ^^^^^^^^^^^--- new!
```

cc ``@Aaron1011`` ``@cjgillot``

clippy_lints/src/blocks_in_if_conditions.rs

@@ -6,7 +6,7 @@ use clippy_utils::ty::implements_trait;
 use if_chain::if_chain;
 use rustc_errors::Applicability;
 use rustc_hir::intravisit::{walk_expr, Visitor};
-use rustc_hir::{BlockCheckMode, Expr, ExprKind};
+use rustc_hir::{BlockCheckMode, Closure, Expr, ExprKind};
 use rustc_lint::{LateContext, LateLintPass, LintContext};
 use rustc_middle::lint::in_external_macro;
 use rustc_session::{declare_lint_pass, declare_tool_lint};
@@ -51,7 +51,7 @@ struct ExVisitor<'a, 'tcx> {
 
 impl<'a, 'tcx> Visitor<'tcx> for ExVisitor<'a, 'tcx> {
     fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
-        if let ExprKind::Closure { body, .. } = expr.kind {
+        if let ExprKind::Closure(&Closure { body, .. }) = expr.kind {
             // do not lint if the closure is called using an iterator (see #1141)
             if_chain! {
                 if let Some(parent) = get_parent_expr(self.cx, expr);

clippy_lints/src/bytecount.rs

@@ -5,7 +5,7 @@ use clippy_utils::visitors::is_local_used;
 use clippy_utils::{path_to_local_id, paths, peel_blocks, peel_ref_operators, strip_pat_refs};
 use if_chain::if_chain;
 use rustc_errors::Applicability;
-use rustc_hir::{BinOpKind, Expr, ExprKind, PatKind};
+use rustc_hir::{BinOpKind, Closure, Expr, ExprKind, PatKind};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_middle::ty::{self, UintTy};
 use rustc_session::{declare_lint_pass, declare_tool_lint};
@@ -51,7 +51,7 @@ impl<'tcx> LateLintPass<'tcx> for ByteCount {
             if count.ident.name == sym::count;
             if let ExprKind::MethodCall(filter, [filter_recv, filter_arg], _) = count_recv.kind;
             if filter.ident.name == sym!(filter);
-            if let ExprKind::Closure { body, .. } = filter_arg.kind;
+            if let ExprKind::Closure(&Closure { body, .. }) = filter_arg.kind;
             let body = cx.tcx.hir().body(body);
             if let [param] = body.params;
             if let PatKind::Binding(_, arg_id, _, _) = strip_pat_refs(param.pat).kind;

clippy_lints/src/eta_reduction.rs

@@ -7,7 +7,7 @@ use clippy_utils::{higher, is_adjusted, path_to_local, path_to_local_id};
 use if_chain::if_chain;
 use rustc_errors::Applicability;
 use rustc_hir::def_id::DefId;
-use rustc_hir::{Expr, ExprKind, Param, PatKind, Unsafety};
+use rustc_hir::{Closure, Expr, ExprKind, Param, PatKind, Unsafety};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_middle::ty::adjustment::{Adjust, Adjustment, AutoBorrow};
 use rustc_middle::ty::binding::BindingMode;
@@ -78,7 +78,7 @@ impl<'tcx> LateLintPass<'tcx> for EtaReduction {
             return;
         }
         let body = match expr.kind {
-            ExprKind::Closure { body, .. } => cx.tcx.hir().body(body),
+            ExprKind::Closure(&Closure { body, .. }) => cx.tcx.hir().body(body),
             _ => return,
         };
         if body.value.span.from_expansion() {

clippy_lints/src/infinite_iter.rs

@@ -1,7 +1,7 @@
 use clippy_utils::diagnostics::span_lint;
 use clippy_utils::ty::{implements_trait, is_type_diagnostic_item};
 use clippy_utils::{higher, match_def_path, path_def_id, paths};
-use rustc_hir::{BorrowKind, Expr, ExprKind};
+use rustc_hir::{BorrowKind, Closure, Expr, ExprKind};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_session::{declare_lint_pass, declare_tool_lint};
 use rustc_span::symbol::{sym, Symbol};
@@ -159,7 +159,7 @@ fn is_infinite(cx: &LateContext<'_>, expr: &Expr<'_>) -> Finiteness {
                 }
             }
             if method.ident.name == sym!(flat_map) && args.len() == 2 {
-                if let ExprKind::Closure { body, .. } = args[1].kind {
+                if let ExprKind::Closure(&Closure { body, .. }) = args[1].kind {
                     let body = cx.tcx.hir().body(body);
                     return is_infinite(cx, &body.value);
                 }

clippy_lints/src/loops/needless_range_loop.rs

@@ -9,7 +9,7 @@ use rustc_ast::ast;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_hir::def::{DefKind, Res};
 use rustc_hir::intravisit::{walk_expr, Visitor};
-use rustc_hir::{BinOpKind, BorrowKind, Expr, ExprKind, HirId, Mutability, Pat, PatKind, QPath};
+use rustc_hir::{BinOpKind, BorrowKind, Closure, Expr, ExprKind, HirId, Mutability, Pat, PatKind, QPath};
 use rustc_lint::LateContext;
 use rustc_middle::middle::region;
 use rustc_middle::ty::{self, Ty};
@@ -369,7 +369,7 @@ impl<'a, 'tcx> Visitor<'tcx> for VarVisitor<'a, 'tcx> {
                     self.visit_expr(expr);
                 }
             },
-            ExprKind::Closure { body, .. } => {
+            ExprKind::Closure(&Closure { body, .. }) => {
                 let body = self.cx.tcx.hir().body(body);
                 self.visit_expr(&body.value);
             },

clippy_lints/src/loops/while_let_on_iterator.rs

@@ -8,7 +8,7 @@ use clippy_utils::{
 use if_chain::if_chain;
 use rustc_errors::Applicability;
 use rustc_hir::intravisit::{walk_expr, Visitor};
-use rustc_hir::{def::Res, Expr, ExprKind, HirId, Local, Mutability, PatKind, QPath, UnOp};
+use rustc_hir::{Closure, def::Res, Expr, ExprKind, HirId, Local, Mutability, PatKind, QPath, UnOp};
 use rustc_lint::LateContext;
 use rustc_middle::ty::adjustment::Adjust;
 use rustc_span::{symbol::sym, Symbol};
@@ -220,7 +220,7 @@ fn uses_iter<'tcx>(cx: &LateContext<'tcx>, iter_expr: &IterExpr, container: &'tc
                 if let Some(e) = e {
                     self.visit_expr(e);
                 }
-            } else if let ExprKind::Closure { body: id, .. } = e.kind {
+            } else if let ExprKind::Closure(&Closure { body: id, .. }) = e.kind {
                 if is_res_used(self.cx, self.iter_expr.path, id) {
                     self.uses_iter = true;
                 }
@@ -260,7 +260,7 @@ fn needs_mutable_borrow(cx: &LateContext<'_>, iter_expr: &IterExpr, loop_expr: &
                     if let Some(e) = e {
                         self.visit_expr(e);
                     }
-                } else if let ExprKind::Closure { body: id, .. } = e.kind {
+                } else if let ExprKind::Closure(&Closure { body: id, .. }) = e.kind {
                     self.used_iter = is_res_used(self.cx, self.iter_expr.path, id);
                 } else {
                     walk_expr(self, e);
@@ -307,7 +307,7 @@ fn needs_mutable_borrow(cx: &LateContext<'_>, iter_expr: &IterExpr, loop_expr: &
                     if let Some(e) = e {
                         self.visit_expr(e);
                     }
-                } else if let ExprKind::Closure { body: id, .. } = e.kind {
+                } else if let ExprKind::Closure(&Closure { body: id, .. }) = e.kind {
                     self.used_after = is_res_used(self.cx, self.iter_expr.path, id);
                 } else {
                     walk_expr(self, e);

clippy_lints/src/manual_async_fn.rs

@@ -6,7 +6,7 @@ use if_chain::if_chain;
 use rustc_errors::Applicability;
 use rustc_hir::intravisit::FnKind;
 use rustc_hir::{
-    AsyncGeneratorKind, Block, Body, Expr, ExprKind, FnDecl, FnRetTy, GeneratorKind, GenericArg, GenericBound, HirId,
+    AsyncGeneratorKind, Block, Body, Closure, Expr, ExprKind, FnDecl, FnRetTy, GeneratorKind, GenericArg, GenericBound, HirId,
     IsAsync, ItemKind, LifetimeName, Term, TraitRef, Ty, TyKind, TypeBindingKind,
 };
 use rustc_lint::{LateContext, LateLintPass};
@@ -177,7 +177,7 @@ fn desugared_async_block<'tcx>(cx: &LateContext<'tcx>, block: &'tcx Block<'tcx>)
         if let Some(block_expr) = block.expr;
         if let Some(args) = match_function_call(cx, block_expr, &FUTURE_FROM_GENERATOR);
         if args.len() == 1;
-        if let Expr{kind: ExprKind::Closure { body, .. }, ..} = args[0];
+        if let Expr{kind: ExprKind::Closure(&Closure { body, .. }), ..} = args[0];
         let closure_body = cx.tcx.hir().body(body);
         if closure_body.generator_kind == Some(GeneratorKind::Async(AsyncGeneratorKind::Block));
         then {

clippy_lints/src/manual_ok_or.rs

@@ -5,7 +5,7 @@ use clippy_utils::{is_lang_ctor, path_to_local_id};
 use if_chain::if_chain;
 use rustc_errors::Applicability;
 use rustc_hir::LangItem::{ResultErr, ResultOk};
-use rustc_hir::{Expr, ExprKind, PatKind};
+use rustc_hir::{Closure, Expr, ExprKind, PatKind};
 use rustc_lint::LintContext;
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_middle::lint::in_external_macro;
@@ -88,7 +88,7 @@ fn is_ok_wrapping(cx: &LateContext<'_>, map_expr: &Expr<'_>) -> bool {
         }
     }
     if_chain! {
-        if let ExprKind::Closure { body, .. } = map_expr.kind;
+        if let ExprKind::Closure(&Closure { body, .. }) = map_expr.kind;
         let body = cx.tcx.hir().body(body);
         if let PatKind::Binding(_, param_id, ..) = body.params[0].pat.kind;
         if let ExprKind::Call(Expr { kind: ExprKind::Path(ok_path), .. }, &[ref ok_arg]) = body.value.kind;

clippy_lints/src/manual_retain.rs

@@ -148,7 +148,7 @@ fn check_to_owned(
 
 fn suggest(cx: &LateContext<'_>, parent_expr: &hir::Expr<'_>, left_expr: &hir::Expr<'_>, filter_expr: &hir::Expr<'_>) {
     if let hir::ExprKind::MethodCall(_, [_, closure], _) = filter_expr.kind
-        && let hir::ExprKind::Closure{ body, ..} = closure.kind
+        && let hir::ExprKind::Closure(&hir::Closure { body, ..}) = closure.kind
         && let filter_body = cx.tcx.hir().body(body)
         && let [filter_params] = filter_body.params
         && let Some(sugg) = match filter_params.pat.kind {

clippy_lints/src/map_clone.rs

@@ -67,7 +67,7 @@ impl<'tcx> LateLintPass<'tcx> for MapClone {
             if method.ident.name == sym::map;
             let ty = cx.typeck_results().expr_ty(&args[0]);
             if is_type_diagnostic_item(cx, ty, sym::Option) || is_trait_method(cx, e, sym::Iterator);
-            if let hir::ExprKind::Closure { body, .. } = args[1].kind;
+            if let hir::ExprKind::Closure(&hir::Closure { body, .. }) = args[1].kind;
             then {
                 let closure_body = cx.tcx.hir().body(body);
                 let closure_expr = peel_blocks(&closure_body.value);

clippy_lints/src/map_err_ignore.rs

@@ -1,5 +1,5 @@
 use clippy_utils::diagnostics::span_lint_and_help;
-use rustc_hir::{CaptureBy, Expr, ExprKind, PatKind};
+use rustc_hir::{CaptureBy, Closure, Expr, ExprKind, PatKind};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_session::{declare_lint_pass, declare_tool_lint};
 
@@ -119,12 +119,12 @@ impl<'tcx> LateLintPass<'tcx> for MapErrIgnore {
             if method.ident.as_str() == "map_err" && args.len() == 2 {
                 // make sure the first argument is a closure, and grab the CaptureRef, BodyId, and fn_decl_span
                 // fields
-                if let ExprKind::Closure {
+                if let ExprKind::Closure(&Closure {
                     capture_clause,
                     body,
                     fn_decl_span,
                     ..
-                } = args[1].kind
+                }) = args[1].kind
                 {
                     // check if this is by Reference (meaning there's no move statement)
                     if capture_clause == CaptureBy::Ref {

clippy_lints/src/map_unit_fn.rs

@@ -169,7 +169,7 @@ fn unit_closure<'tcx>(
     expr: &hir::Expr<'_>,
 ) -> Option<(&'tcx hir::Param<'tcx>, &'tcx hir::Expr<'tcx>)> {
     if_chain! {
-        if let hir::ExprKind::Closure { fn_decl, body, .. } = expr.kind;
+        if let hir::ExprKind::Closure(&hir::Closure { fn_decl, body, .. }) = expr.kind;
         let body = cx.tcx.hir().body(body);
         let body_expr = &body.value;
         if fn_decl.inputs.len() == 1;

clippy_lints/src/methods/bind_instead_of_map.rs

@@ -150,7 +150,7 @@ pub(crate) trait BindInsteadOfMap {
         }
 
         match arg.kind {
-            hir::ExprKind::Closure { body, fn_decl_span, .. } => {
+            hir::ExprKind::Closure(&hir::Closure { body, fn_decl_span, .. }) => {
                 let closure_body = cx.tcx.hir().body(body);
                 let closure_expr = peel_blocks(&closure_body.value);
 

clippy_lints/src/methods/filter_map.rs

@@ -6,7 +6,7 @@ use if_chain::if_chain;
 use rustc_errors::Applicability;
 use rustc_hir as hir;
 use rustc_hir::def::Res;
-use rustc_hir::{Expr, ExprKind, PatKind, PathSegment, QPath, UnOp};
+use rustc_hir::{Closure, Expr, ExprKind, PatKind, PathSegment, QPath, UnOp};
 use rustc_lint::LateContext;
 use rustc_span::source_map::Span;
 use rustc_span::symbol::{sym, Symbol};
@@ -22,8 +22,8 @@ fn is_method<'tcx>(cx: &LateContext<'tcx>, expr: &hir::Expr<'_>, method_name: Sy
         hir::ExprKind::Path(QPath::Resolved(_, segments)) => {
             segments.segments.last().unwrap().ident.name == method_name
         },
-        hir::ExprKind::Closure { body, .. } => {
-            let body = cx.tcx.hir().body(*body);
+        hir::ExprKind::Closure(&hir::Closure { body, .. }) => {
+            let body = cx.tcx.hir().body(body);
             let closure_expr = peel_blocks(&body.value);
             let arg_id = body.params[0].pat.hir_id;
             match closure_expr.kind {
@@ -106,7 +106,7 @@ pub(super) fn check<'tcx>(
             if is_trait_method(cx, map_recv, sym::Iterator);
 
             // filter(|x| ...is_some())...
-            if let ExprKind::Closure { body: filter_body_id, .. } = filter_arg.kind;
+            if let ExprKind::Closure(&Closure { body: filter_body_id, .. }) = filter_arg.kind;
             let filter_body = cx.tcx.hir().body(filter_body_id);
             if let [filter_param] = filter_body.params;
             // optional ref pattern: `filter(|&x| ..)`
@@ -129,7 +129,7 @@ pub(super) fn check<'tcx>(
             if path.ident.name.as_str() == if is_result { "is_ok" } else { "is_some" };
 
             // ...map(|x| ...unwrap())
-            if let ExprKind::Closure { body: map_body_id, .. } = map_arg.kind;
+            if let ExprKind::Closure(&Closure { body: map_body_id, .. }) = map_arg.kind;
             let map_body = cx.tcx.hir().body(map_body_id);
             if let [map_param] = map_body.params;
             if let PatKind::Binding(_, map_param_id, map_param_ident, None) = map_param.pat.kind;

clippy_lints/src/methods/option_as_ref_deref.rs

@@ -51,7 +51,7 @@ pub(super) fn check<'tcx>(
             .map_or(false, |fun_def_id| {
                 deref_aliases.iter().any(|path| match_def_path(cx, fun_def_id, path))
             }),
-        hir::ExprKind::Closure { body, .. } => {
+        hir::ExprKind::Closure(&hir::Closure { body, .. }) => {
             let closure_body = cx.tcx.hir().body(body);
             let closure_expr = peel_blocks(&closure_body.value);
 

clippy_lints/src/methods/option_map_or_none.rs

@@ -71,7 +71,7 @@ pub(super) fn check<'tcx>(
     if is_option {
         let self_snippet = snippet(cx, recv.span, "..");
         if_chain! {
-            if let hir::ExprKind::Closure { body, fn_decl_span, .. } = map_arg.kind;
+            if let hir::ExprKind::Closure(&hir::Closure { body, fn_decl_span, .. }) = map_arg.kind;
             let arg_snippet = snippet(cx, fn_decl_span, "..");
             let body = cx.tcx.hir().body(body);
             if let Some((func, [arg_char])) = reduce_unit_expression(&body.value);

clippy_lints/src/methods/search_is_some.rs

@@ -41,7 +41,7 @@ pub(super) fn check<'tcx>(
             let mut applicability = Applicability::MachineApplicable;
             let any_search_snippet = if_chain! {
                 if search_method == "find";
-                if let hir::ExprKind::Closure { body, .. } = search_arg.kind;
+                if let hir::ExprKind::Closure(&hir::Closure { body, .. }) = search_arg.kind;
                 let closure_body = cx.tcx.hir().body(body);
                 if let Some(closure_arg) = closure_body.params.get(0);
                 then {

clippy_lints/src/methods/unnecessary_filter_map.rs

@@ -18,7 +18,7 @@ pub(super) fn check(cx: &LateContext<'_>, expr: &hir::Expr<'_>, arg: &hir::Expr<
         return;
     }
 
-    if let hir::ExprKind::Closure { body, .. } = arg.kind {
+    if let hir::ExprKind::Closure(&hir::Closure { body, .. }) = arg.kind {
         let body = cx.tcx.hir().body(body);
         let arg_id = body.params[0].pat.hir_id;
         let mutates_arg =

clippy_lints/src/methods/unnecessary_fold.rs

@@ -29,7 +29,7 @@ pub(super) fn check(
     ) {
         if_chain! {
             // Extract the body of the closure passed to fold
-            if let hir::ExprKind::Closure { body, .. } = acc.kind;
+            if let hir::ExprKind::Closure(&hir::Closure { body, .. }) = acc.kind;
             let closure_body = cx.tcx.hir().body(body);
             let closure_expr = peel_blocks(&closure_body.value);
 

clippy_lints/src/methods/unnecessary_lazy_eval.rs

@@ -22,7 +22,7 @@ pub(super) fn check<'tcx>(
     let is_result = is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(recv), sym::Result);
 
     if is_option || is_result {
-        if let hir::ExprKind::Closure { body, .. } = arg.kind {
+        if let hir::ExprKind::Closure(&hir::Closure { body, .. }) = arg.kind {
             let body = cx.tcx.hir().body(body);
             let body_expr = &body.value;
 

clippy_lints/src/needless_for_each.rs

@@ -1,7 +1,7 @@
 use rustc_errors::Applicability;
 use rustc_hir::{
     intravisit::{walk_expr, Visitor},
-    Expr, ExprKind, Stmt, StmtKind,
+    Closure, Expr, ExprKind, Stmt, StmtKind,
 };
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_session::{declare_lint_pass, declare_tool_lint};
@@ -72,7 +72,7 @@ impl<'tcx> LateLintPass<'tcx> for NeedlessForEach {
             if has_iter_method(cx, cx.typeck_results().expr_ty(iter_recv)).is_some();
             // Skip the lint if the body is not block because this is simpler than `for` loop.
             // e.g. `v.iter().for_each(f)` is simpler and clearer than using `for` loop.
-            if let ExprKind::Closure { body, .. } = for_each_arg.kind;
+            if let ExprKind::Closure(&Closure { body, .. }) = for_each_arg.kind;
             let body = cx.tcx.hir().body(body);
             if let ExprKind::Block(..) = body.value.kind;
             then {

clippy_lints/src/only_used_in_recursion.rs

@@ -11,7 +11,7 @@ use rustc_hir::def_id::DefId;
 use rustc_hir::definitions::{DefPathData, DisambiguatedDefPathData};
 use rustc_hir::intravisit::{walk_expr, walk_stmt, FnKind, Visitor};
 use rustc_hir::{
-    Arm, Block, Body, Expr, ExprKind, Guard, HirId, ImplicitSelfKind, Let, Local, Pat, PatKind, Path, PathSegment,
+    Arm, Closure, Block, Body, Expr, ExprKind, Guard, HirId, ImplicitSelfKind, Let, Local, Pat, PatKind, Path, PathSegment,
     QPath, Stmt, StmtKind, TyKind, UnOp,
 };
 use rustc_lint::{LateContext, LateLintPass};
@@ -298,7 +298,7 @@ impl<'tcx> Visitor<'tcx> for SideEffectVisit<'tcx> {
             },
             ExprKind::Match(expr, arms, _) => self.visit_match(expr, arms),
             // since analysing the closure is not easy, just set all variables in it to side-effect
-            ExprKind::Closure { body, .. } => {
+            ExprKind::Closure(&Closure { body, .. }) => {
                 let body = self.tcx.hir().body(body);
                 self.visit_body(body);
                 let vars = std::mem::take(&mut self.ret_vars);

clippy_lints/src/redundant_closure_call.rs

@@ -69,7 +69,7 @@ impl EarlyLintPass for RedundantClosureCall {
         if_chain! {
             if let ast::ExprKind::Call(ref paren, _) = expr.kind;
             if let ast::ExprKind::Paren(ref closure) = paren.kind;
-            if let ast::ExprKind::Closure(_, _, _, ref decl, ref block, _) = closure.kind;
+            if let ast::ExprKind::Closure(_, _, _, _, ref decl, ref block, _) = closure.kind;
             then {
                 let mut visitor = ReturnVisitor::new();
                 visitor.visit_expr(block);

clippy_lints/src/suspicious_operation_groupings.rs

@@ -582,7 +582,7 @@ fn ident_difference_expr_with_base_location(
         | (Await(_), Await(_))
         | (Async(_, _, _), Async(_, _, _))
         | (Block(_, _), Block(_, _))
-        | (Closure(_, _, _, _, _, _), Closure(_, _, _, _, _, _))
+        | (Closure(_, _, _, _, _, _, _), Closure(_, _, _, _, _, _, _))
         | (Match(_, _), Match(_, _))
         | (Loop(_, _), Loop(_, _))
         | (ForLoop(_, _, _, _), ForLoop(_, _, _, _))

clippy_lints/src/unit_return_expecting_ord.rs

@@ -2,7 +2,7 @@ use clippy_utils::diagnostics::{span_lint, span_lint_and_help};
 use clippy_utils::{get_trait_def_id, paths};
 use if_chain::if_chain;
 use rustc_hir::def_id::DefId;
-use rustc_hir::{Expr, ExprKind, StmtKind};
+use rustc_hir::{Closure, Expr, ExprKind, StmtKind};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_middle::ty;
 use rustc_middle::ty::{GenericPredicates, PredicateKind, ProjectionPredicate, TraitPredicate};
@@ -116,7 +116,7 @@ fn get_args_to_check<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) -> Ve
 
 fn check_arg<'tcx>(cx: &LateContext<'tcx>, arg: &'tcx Expr<'tcx>) -> Option<(Span, Option<Span>)> {
     if_chain! {
-        if let ExprKind::Closure { body, fn_decl_span, .. } = arg.kind;
+        if let ExprKind::Closure(&Closure { body, fn_decl_span, .. }) = arg.kind;
         if let ty::Closure(_def_id, substs) = &cx.typeck_results().node_type(arg.hir_id).kind();
         let ret_ty = substs.as_closure().sig().output();
         let ty = cx.tcx.erase_late_bound_regions(ret_ty);