Remove identity_future indirection

This was previously needed because the indirection used to hide some unexplained lifetime errors, which it turned out were related to the `min_choice` algorithm.

Removing the indirection also solves a couple of cycle errors, large moves and makes async blocks support the `#[track_caller]` annotation.

clippy_lints/src/manual_async_fn.rs

@@ -1,5 +1,4 @@
 use clippy_utils::diagnostics::span_lint_and_then;
-use clippy_utils::match_function_call_with_def_id;
 use clippy_utils::source::{position_before_rarrow, snippet_block, snippet_opt};
 use if_chain::if_chain;
 use rustc_errors::Applicability;
@@ -175,16 +174,10 @@ fn captures_all_lifetimes(inputs: &[Ty<'_>], output_lifetimes: &[LifetimeName])
 fn desugared_async_block<'tcx>(cx: &LateContext<'tcx>, block: &'tcx Block<'tcx>) -> Option<&'tcx Body<'tcx>> {
     if_chain! {
         if let Some(block_expr) = block.expr;
-        if let Some(args) = cx
-            .tcx
-            .lang_items()
-            .identity_future_fn()
-            .and_then(|def_id| match_function_call_with_def_id(cx, block_expr, def_id));
-        if args.len() == 1;
         if let Expr {
             kind: ExprKind::Closure(&Closure { body, .. }),
             ..
-        } = args[0];
+        } = block_expr;
         let closure_body = cx.tcx.hir().body(body);
         if closure_body.generator_kind == Some(GeneratorKind::Async(AsyncGeneratorKind::Block));
         then {

clippy_utils/src/lib.rs

@@ -1904,16 +1904,7 @@ pub fn is_async_fn(kind: FnKind<'_>) -> bool {
 
 /// Peels away all the compiler generated code surrounding the body of an async function,
 pub fn get_async_fn_body<'tcx>(tcx: TyCtxt<'tcx>, body: &Body<'_>) -> Option<&'tcx Expr<'tcx>> {
-    if let ExprKind::Call(
-        _,
-        &[
-            Expr {
-                kind: ExprKind::Closure(&Closure { body, .. }),
-                ..
-            },
-        ],
-    ) = body.value.kind
-    {
+    if let ExprKind::Closure(&Closure { body, .. }) = body.value.kind {
         if let ExprKind::Block(
             Block {
                 stmts: [],

tests/ui/author/blocks.stdout

@@ -43,11 +43,7 @@ if let ExprKind::Block(block, None) = expr.kind
 if let ExprKind::Closure(CaptureBy::Value, fn_decl, body_id, _, None) = expr.kind
     && let FnRetTy::DefaultReturn(_) = fn_decl.output
     && expr1 = &cx.tcx.hir().body(body_id).value
-    && let ExprKind::Call(func, args) = expr1.kind
-    && let ExprKind::Path(ref qpath) = func.kind
-    && matches!(qpath, QPath::LangItem(LangItem::IdentityFuture, _))
-    && args.len() == 1
-    && let ExprKind::Closure(CaptureBy::Value, fn_decl1, body_id1, _, Some(Movability::Static)) = args[0].kind
+    && let ExprKind::Closure(CaptureBy::Value, fn_decl1, body_id1, _, Some(Movability::Static)) = expr1.kind
     && let FnRetTy::DefaultReturn(_) = fn_decl1.output
     && expr2 = &cx.tcx.hir().body(body_id1).value
     && let ExprKind::Block(block, None) = expr2.kind