From 0253be53b706d59da904acbab2a0fca618b7b4f6 Mon Sep 17 00:00:00 2001
From: Oli Scherer <git-spam-no-reply9815368754983@oli-obk.de>
Date: Thu, 11 Apr 2024 12:48:32 +0000
Subject: [PATCH] Add explicit syntax for coroutines instead of relying on
 closures having `yield` expressions

---
 compiler/rustc_ast_lowering/src/expr.rs        | 12 +++++++++++-
 compiler/rustc_feature/src/builtin_attrs.rs    |  6 ++++++
 tests/ui/coroutine/derived-drop-parent-expr.rs |  4 ++--
 3 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/compiler/rustc_ast_lowering/src/expr.rs b/compiler/rustc_ast_lowering/src/expr.rs
index 2305cc07795db..6c3f03431472b 100644
--- a/compiler/rustc_ast_lowering/src/expr.rs
+++ b/compiler/rustc_ast_lowering/src/expr.rs
@@ -217,6 +217,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                         binder,
                         *capture_clause,
                         e.id,
+                        hir_id,
                         *constness,
                         *movability,
                         fn_decl,
@@ -955,6 +956,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         binder: &ClosureBinder,
         capture_clause: CaptureBy,
         closure_id: NodeId,
+        closure_hir_id: hir::HirId,
         constness: Const,
         movability: Movability,
         decl: &FnDecl,
@@ -965,7 +967,15 @@ impl<'hir> LoweringContext<'_, 'hir> {
         let (binder_clause, generic_params) = self.lower_closure_binder(binder);
 
         let (body_id, closure_kind) = self.with_new_scopes(fn_decl_span, move |this| {
-            let mut coroutine_kind = None;
+            let mut coroutine_kind = if this
+                .attrs
+                .get(&closure_hir_id.local_id)
+                .is_some_and(|attrs| attrs.iter().any(|attr| attr.has_name(sym::coroutine)))
+            {
+                Some(hir::CoroutineKind::Coroutine(Movability::Movable))
+            } else {
+                None
+            };
             let body_id = this.lower_fn_body(decl, |this| {
                 let e = this.lower_expr_mut(body);
                 coroutine_kind = this.coroutine_kind;
diff --git a/compiler/rustc_feature/src/builtin_attrs.rs b/compiler/rustc_feature/src/builtin_attrs.rs
index 4f62323231a73..2c5511d67fd0b 100644
--- a/compiler/rustc_feature/src/builtin_attrs.rs
+++ b/compiler/rustc_feature/src/builtin_attrs.rs
@@ -534,6 +534,12 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         EncodeCrossCrate::Yes, experimental!(cfi_encoding)
     ),
 
+    // `#[coroutine]` attribute to be applied to closures to make them coroutines instead
+    gated!(
+        coroutine, Normal, template!(Word), ErrorFollowing,
+        EncodeCrossCrate::No, coroutines, experimental!(coroutines)
+    ),
+
     // ==========================================================================
     // Internal attributes: Stability, deprecation, and unsafe:
     // ==========================================================================
diff --git a/tests/ui/coroutine/derived-drop-parent-expr.rs b/tests/ui/coroutine/derived-drop-parent-expr.rs
index f70a732c90f08..71f7506ab845e 100644
--- a/tests/ui/coroutine/derived-drop-parent-expr.rs
+++ b/tests/ui/coroutine/derived-drop-parent-expr.rs
@@ -10,7 +10,7 @@ pub struct Client { pub nickname: String }
 
 fn main() {
     let g = move || match drop(Client { ..Client::default() }) {
-        _status => yield,
-    };
+            _status => yield,
+        };
     assert_send(g);
 }