Rollup merge of #119967 - ShE3py:patkind-err, r=WaffleLapkin

Add `PatKind::Err` to AST/HIR

#116715 added `thir::PatKind::Error`; this PR adds `hir::PatKind::Err` and `ast::PatKind::Err` (see https://github.com/rust-lang/rust/pull/118625#discussion_r1446587901.)

---

``@rustbot`` label +A-patterns
r? WaffleLapkin

3 files changed, 7 insertions, 3 deletions

diff --git a/compiler/rustc_ast/src/ast.rs b/compiler/rustc_ast/src/ast.rs
index 21077c312bd..d0d98eb3d62 100644
--- a/compiler/rustc_ast/src/ast.rs
+++ b/compiler/rustc_ast/src/ast.rs
@@ -625,7 +625,8 @@ impl Pat {
             | PatKind::Range(..)
             | PatKind::Ident(..)
             | PatKind::Path(..)
-            | PatKind::MacCall(_) => {}
+            | PatKind::MacCall(_)
+            | PatKind::Err(_) => {}
         }
     }
 
@@ -809,6 +810,9 @@ pub enum PatKind {
 
     /// A macro pattern; pre-expansion.
     MacCall(P<MacCall>),
+
+    /// Placeholder for a pattern that wasn't syntactically well formed in some way.
+    Err(ErrorGuaranteed),
 }
 
 /// Whether the `..` is present in a struct fields pattern.
diff --git a/compiler/rustc_ast/src/mut_visit.rs b/compiler/rustc_ast/src/mut_visit.rs
index 450555d0cb5..90677151d25 100644
--- a/compiler/rustc_ast/src/mut_visit.rs
+++ b/compiler/rustc_ast/src/mut_visit.rs
@@ -1267,7 +1267,7 @@ pub fn noop_visit_pat<T: MutVisitor>(pat: &mut P<Pat>, vis: &mut T) {
     let Pat { id, kind, span, tokens } = pat.deref_mut();
     vis.visit_id(id);
     match kind {
-        PatKind::Wild | PatKind::Rest | PatKind::Never => {}
+        PatKind::Wild | PatKind::Rest | PatKind::Never | PatKind::Err(_) => {}
         PatKind::Ident(_binding_mode, ident, sub) => {
             vis.visit_ident(ident);
             visit_opt(sub, |sub| vis.visit_pat(sub));
diff --git a/compiler/rustc_ast/src/visit.rs b/compiler/rustc_ast/src/visit.rs
index 3617df931e2..89f50d3a0a7 100644
--- a/compiler/rustc_ast/src/visit.rs
+++ b/compiler/rustc_ast/src/visit.rs
@@ -568,7 +568,7 @@ pub fn walk_pat<'a, V: Visitor<'a>>(visitor: &mut V, pattern: &'a Pat) {
             walk_list!(visitor, visit_expr, lower_bound);
             walk_list!(visitor, visit_expr, upper_bound);
         }
-        PatKind::Wild | PatKind::Rest | PatKind::Never => {}
+        PatKind::Wild | PatKind::Rest | PatKind::Never | PatKind::Err(_) => {}
         PatKind::Tuple(elems) | PatKind::Slice(elems) | PatKind::Or(elems) => {
             walk_list!(visitor, visit_pat, elems);
         }