From 80bdcbf50a63845dd3cfeb05751ba3dcbd1025b8 Mon Sep 17 00:00:00 2001
From: Nadrieril <nadrieril+git@gmail.com>
Date: Mon, 27 Nov 2023 03:15:56 +0100
Subject: Parse a pattern with no arm

---
 compiler/rustc_ast/src/ast.rs       | 22 ++++++++++++++++++++--
 compiler/rustc_ast/src/mut_visit.rs |  2 +-
 compiler/rustc_ast/src/visit.rs     |  2 +-
 3 files changed, 22 insertions(+), 4 deletions(-)

(limited to 'compiler/rustc_ast')

diff --git a/compiler/rustc_ast/src/ast.rs b/compiler/rustc_ast/src/ast.rs
index cba9121aa5a..62bacf97f49 100644
--- a/compiler/rustc_ast/src/ast.rs
+++ b/compiler/rustc_ast/src/ast.rs
@@ -658,6 +658,24 @@ impl Pat {
     pub fn is_rest(&self) -> bool {
         matches!(self.kind, PatKind::Rest)
     }
+
+    /// Could this be a never pattern? I.e. is it a never pattern modulo macro invocations that
+    /// might return never patterns?
+    pub fn could_be_never_pattern(&self) -> bool {
+        let mut could_be_never_pattern = false;
+        self.walk(&mut |pat| match &pat.kind {
+            PatKind::Never | PatKind::MacCall(_) => {
+                could_be_never_pattern = true;
+                false
+            }
+            PatKind::Or(s) => {
+                could_be_never_pattern = s.iter().all(|p| p.could_be_never_pattern());
+                false
+            }
+            _ => true,
+        });
+        could_be_never_pattern
+    }
 }
 
 /// A single field in a struct pattern.
@@ -1080,8 +1098,8 @@ pub struct Arm {
     pub pat: P<Pat>,
     /// Match arm guard, e.g. `n > 10` in `match foo { n if n > 10 => {}, _ => {} }`
     pub guard: Option<P<Expr>>,
-    /// Match arm body.
-    pub body: P<Expr>,
+    /// Match arm body. Omitted if the pattern is a never pattern.
+    pub body: Option<P<Expr>>,
     pub span: Span,
     pub id: NodeId,
     pub is_placeholder: bool,
diff --git a/compiler/rustc_ast/src/mut_visit.rs b/compiler/rustc_ast/src/mut_visit.rs
index 8ce86bf9ecf..e909e8dc774 100644
--- a/compiler/rustc_ast/src/mut_visit.rs
+++ b/compiler/rustc_ast/src/mut_visit.rs
@@ -453,7 +453,7 @@ pub fn noop_flat_map_arm<T: MutVisitor>(mut arm: Arm, vis: &mut T) -> SmallVec<[
     vis.visit_id(id);
     vis.visit_pat(pat);
     visit_opt(guard, |guard| vis.visit_expr(guard));
-    vis.visit_expr(body);
+    visit_opt(body, |body| vis.visit_expr(body));
     vis.visit_span(span);
     smallvec![arm]
 }
diff --git a/compiler/rustc_ast/src/visit.rs b/compiler/rustc_ast/src/visit.rs
index 9dbadcb49d3..773a7ebc707 100644
--- a/compiler/rustc_ast/src/visit.rs
+++ b/compiler/rustc_ast/src/visit.rs
@@ -951,7 +951,7 @@ pub fn walk_param<'a, V: Visitor<'a>>(visitor: &mut V, param: &'a Param) {
 pub fn walk_arm<'a, V: Visitor<'a>>(visitor: &mut V, arm: &'a Arm) {
     visitor.visit_pat(&arm.pat);
     walk_list!(visitor, visit_expr, &arm.guard);
-    visitor.visit_expr(&arm.body);
+    walk_list!(visitor, visit_expr, &arm.body);
     walk_list!(visitor, visit_attribute, &arm.attrs);
 }
 
-- 
cgit 1.4.1-3-g733a5