3 files changed, 42 insertions, 50 deletions
diff --git a/compiler/rustc_ast/src/ast.rs b/compiler/rustc_ast/src/ast.rs
index 4ef8d64c4c0..bf648388f4e 100644
--- a/compiler/rustc_ast/src/ast.rs
+++ b/compiler/rustc_ast/src/ast.rs
@@ -1311,7 +1311,7 @@ pub struct Closure {
     pub binder: ClosureBinder,
     pub capture_clause: CaptureBy,
     pub constness: Const,
-    pub asyncness: Async,
+    pub coro_kind: CoroutineKind,
     pub movability: Movability,
     pub fn_decl: P<FnDecl>,
     pub body: P<Expr>,
@@ -2406,28 +2406,38 @@ pub enum Unsafe {
     No,
 }
 
+/// Describes what kind of coroutine markers, if any, a function has.
+///
+/// Coroutine markers are things that cause the function to generate a coroutine, such as `async`,
+/// which makes the function return `impl Future`, or `gen`, which makes the function return `impl
+/// Iterator`.
 #[derive(Copy, Clone, Encodable, Decodable, Debug)]
-pub enum Async {
-    Yes { span: Span, closure_id: NodeId, return_impl_trait_id: NodeId },
-    No,
-}
-
-#[derive(Copy, Clone, Encodable, Decodable, Debug)]
-pub enum Gen {
-    Yes { span: Span, closure_id: NodeId, return_impl_trait_id: NodeId },
-    No,
+pub enum CoroutineKind {
+    /// `async`, which evaluates to `impl Future`
+    Async { span: Span, closure_id: NodeId, return_impl_trait_id: NodeId },
+    /// `gen`, which evaluates to `impl Iterator`
+    Gen { span: Span, closure_id: NodeId, return_impl_trait_id: NodeId },
+    /// Neither `async` nor `gen`
+    None,
 }
 
-impl Async {
+impl CoroutineKind {
     pub fn is_async(self) -> bool {
-        matches!(self, Async::Yes { .. })
+        matches!(self, CoroutineKind::Async { .. })
+    }
+
+    pub fn is_gen(self) -> bool {
+        matches!(self, CoroutineKind::Gen { .. })
     }
 
     /// In this case this is an `async` return, the `NodeId` for the generated `impl Trait` item.
     pub fn opt_return_id(self) -> Option<(NodeId, Span)> {
         match self {
-            Async::Yes { return_impl_trait_id, span, .. } => Some((return_impl_trait_id, span)),
-            Async::No => None,
+            CoroutineKind::Async { return_impl_trait_id, span, .. }
+            | CoroutineKind::Gen { return_impl_trait_id, span, .. } => {
+                Some((return_impl_trait_id, span))
+            }
+            CoroutineKind::None => None,
         }
     }
 }
@@ -2831,25 +2841,22 @@ impl Extern {
 pub struct FnHeader {
     /// The `unsafe` keyword, if any
     pub unsafety: Unsafe,
-    /// The `async` keyword, if any
-    pub asyncness: Async,
+    /// Whether this is `async`, `gen`, or nothing.
+    pub coro_kind: CoroutineKind,
     /// The `const` keyword, if any
     pub constness: Const,
     /// The `extern` keyword and corresponding ABI string, if any
     pub ext: Extern,
-    /// The `gen` keyword, if any
-    pub genness: Gen,
 }
 
 impl FnHeader {
     /// Does this function header have any qualifiers or is it empty?
     pub fn has_qualifiers(&self) -> bool {
-        let Self { unsafety, asyncness, constness, ext, genness } = self;
+        let Self { unsafety, coro_kind, constness, ext } = self;
         matches!(unsafety, Unsafe::Yes(_))
-            || asyncness.is_async()
+            || !matches!(coro_kind, CoroutineKind::None)
             || matches!(constness, Const::Yes(_))
             || !matches!(ext, Extern::None)
-            || matches!(genness, Gen::Yes { .. })
     }
 }
 
@@ -2857,10 +2864,9 @@ impl Default for FnHeader {
     fn default() -> FnHeader {
         FnHeader {
             unsafety: Unsafe::No,
-            asyncness: Async::No,
+            coro_kind: CoroutineKind::None,
             constness: Const::No,
             ext: Extern::None,
-            genness: Gen::No,
         }
     }
 }
@@ -3181,7 +3187,7 @@ mod size_asserts {
     static_assert_size!(Block, 32);
     static_assert_size!(Expr, 72);
     static_assert_size!(ExprKind, 40);
-    static_assert_size!(Fn, 168);
+    static_assert_size!(Fn, 160);
     static_assert_size!(ForeignItem, 96);
     static_assert_size!(ForeignItemKind, 24);
     static_assert_size!(GenericArg, 24);
diff --git a/compiler/rustc_ast/src/mut_visit.rs b/compiler/rustc_ast/src/mut_visit.rs
index 7cdbb1a8c61..f9f767862f5 100644
--- a/compiler/rustc_ast/src/mut_visit.rs
+++ b/compiler/rustc_ast/src/mut_visit.rs
@@ -121,12 +121,8 @@ pub trait MutVisitor: Sized {
         noop_visit_fn_decl(d, self);
     }
 
-    fn visit_asyncness(&mut self, a: &mut Async) {
-        noop_visit_asyncness(a, self);
-    }
-
-    fn visit_genness(&mut self, a: &mut Gen) {
-        noop_visit_genness(a, self);
+    fn visit_coro_kind(&mut self, a: &mut CoroutineKind) {
+        noop_visit_coro_kind(a, self);
     }
 
     fn visit_closure_binder(&mut self, b: &mut ClosureBinder) {
@@ -875,23 +871,14 @@ pub fn noop_visit_closure_binder<T: MutVisitor>(binder: &mut ClosureBinder, vis:
     }
 }
 
-pub fn noop_visit_asyncness<T: MutVisitor>(asyncness: &mut Async, vis: &mut T) {
-    match asyncness {
-        Async::Yes { span: _, closure_id, return_impl_trait_id } => {
-            vis.visit_id(closure_id);
-            vis.visit_id(return_impl_trait_id);
-        }
-        Async::No => {}
-    }
-}
-
-pub fn noop_visit_genness<T: MutVisitor>(genness: &mut Gen, vis: &mut T) {
-    match genness {
-        Gen::Yes { span: _, closure_id, return_impl_trait_id } => {
+pub fn noop_visit_coro_kind<T: MutVisitor>(coro_kind: &mut CoroutineKind, vis: &mut T) {
+    match coro_kind {
+        CoroutineKind::Async { span: _, closure_id, return_impl_trait_id }
+        | CoroutineKind::Gen { span: _, closure_id, return_impl_trait_id } => {
             vis.visit_id(closure_id);
             vis.visit_id(return_impl_trait_id);
         }
-        Gen::No => {}
+        CoroutineKind::None => {}
     }
 }
 
@@ -1184,10 +1171,9 @@ fn visit_const_item<T: MutVisitor>(
 }
 
 pub fn noop_visit_fn_header<T: MutVisitor>(header: &mut FnHeader, vis: &mut T) {
-    let FnHeader { unsafety, asyncness, constness, ext: _, genness } = header;
+    let FnHeader { unsafety, coro_kind, constness, ext: _ } = header;
     visit_constness(constness, vis);
-    vis.visit_asyncness(asyncness);
-    vis.visit_genness(genness);
+    vis.visit_coro_kind(coro_kind);
     visit_unsafety(unsafety, vis);
 }
 
@@ -1421,7 +1407,7 @@ pub fn noop_visit_expr<T: MutVisitor>(
             binder,
             capture_clause,
             constness,
-            asyncness,
+            coro_kind,
             movability: _,
             fn_decl,
             body,
@@ -1430,7 +1416,7 @@ pub fn noop_visit_expr<T: MutVisitor>(
         }) => {
             vis.visit_closure_binder(binder);
             visit_constness(constness, vis);
-            vis.visit_asyncness(asyncness);
+            vis.visit_coro_kind(coro_kind);
             vis.visit_capture_by(capture_clause);
             vis.visit_fn_decl(fn_decl);
             vis.visit_expr(body);
diff --git a/compiler/rustc_ast/src/visit.rs b/compiler/rustc_ast/src/visit.rs
index 9dbadcb49d3..a303d6584f4 100644
--- a/compiler/rustc_ast/src/visit.rs
+++ b/compiler/rustc_ast/src/visit.rs
@@ -861,7 +861,7 @@ pub fn walk_expr<'a, V: Visitor<'a>>(visitor: &mut V, expression: &'a Expr) {
         ExprKind::Closure(box Closure {
             binder,
             capture_clause,
-            asyncness: _,
+            coro_kind: _,
             constness: _,
             movability: _,
             fn_decl,