Add `PatKind::Err`

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.

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));

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);
         }

compiler/rustc_ast_lowering/src/pat.rs

@@ -109,6 +109,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                     // return inner to be processed in next loop
                     PatKind::Paren(inner) => pattern = inner,
                     PatKind::MacCall(_) => panic!("{:?} shouldn't exist here", pattern.span),
+                    PatKind::Err(guar) => break hir::PatKind::Err(*guar),
                 }
             };
 

compiler/rustc_ast_pretty/src/pprust/state.rs

@@ -1519,6 +1519,11 @@ impl<'a> State<'a> {
                 self.pclose();
             }
             PatKind::MacCall(m) => self.print_mac(m),
+            PatKind::Err(_) => {
+                self.popen();
+                self.word("/*ERROR*/");
+                self.pclose();
+            }
         }
         self.ann.post(self, AnnNode::Pat(pat))
     }

compiler/rustc_hir/src/hir.rs

@@ -1015,7 +1015,7 @@ impl<'hir> Pat<'hir> {
 
         use PatKind::*;
         match self.kind {
-            Wild | Never | Lit(_) | Range(..) | Binding(.., None) | Path(_) => true,
+            Wild | Never | Lit(_) | Range(..) | Binding(.., None) | Path(_) | Err(_) => true,
             Box(s) | Ref(s, _) | Binding(.., Some(s)) => s.walk_short_(it),
             Struct(_, fields, _) => fields.iter().all(|field| field.pat.walk_short_(it)),
             TupleStruct(_, s, _) | Tuple(s, _) | Or(s) => s.iter().all(|p| p.walk_short_(it)),
@@ -1042,7 +1042,7 @@ impl<'hir> Pat<'hir> {
 
         use PatKind::*;
         match self.kind {
-            Wild | Never | Lit(_) | Range(..) | Binding(.., None) | Path(_) => {}
+            Wild | Never | Lit(_) | Range(..) | Binding(.., None) | Path(_) | Err(_) => {}
             Box(s) | Ref(s, _) | Binding(.., Some(s)) => s.walk_(it),
             Struct(_, fields, _) => fields.iter().for_each(|field| field.pat.walk_(it)),
             TupleStruct(_, s, _) | Tuple(s, _) | Or(s) => s.iter().for_each(|p| p.walk_(it)),
@@ -1205,6 +1205,9 @@ pub enum PatKind<'hir> {
     /// PatKind::Slice([Binding(a), Binding(b)], Some(Wild), [Binding(c), Binding(d)])
     /// ```
     Slice(&'hir [Pat<'hir>], Option<&'hir Pat<'hir>>, &'hir [Pat<'hir>]),
+
+    /// A placeholder for a pattern that wasn't well formed in some way.
+    Err(ErrorGuaranteed),
 }
 
 /// A statement.

compiler/rustc_hir/src/intravisit.rs

@@ -655,7 +655,7 @@ pub fn walk_pat<'v, V: Visitor<'v>>(visitor: &mut V, pattern: &'v Pat<'v>) {
             walk_list!(visitor, visit_expr, lower_bound);
             walk_list!(visitor, visit_expr, upper_bound);
         }
-        PatKind::Never | PatKind::Wild => (),
+        PatKind::Never | PatKind::Wild | PatKind::Err(_) => (),
         PatKind::Slice(prepatterns, ref slice_pattern, postpatterns) => {
             walk_list!(visitor, visit_pat, prepatterns);
             walk_list!(visitor, visit_pat, slice_pattern);

compiler/rustc_hir_analysis/src/check/region.rs

@@ -681,7 +681,8 @@ fn resolve_local<'tcx>(
             | PatKind::Never
             | PatKind::Path(_)
             | PatKind::Lit(_)
-            | PatKind::Range(_, _, _) => false,
+            | PatKind::Range(_, _, _)
+            | PatKind::Err(_) => false,
         }
     }
 

compiler/rustc_hir_pretty/src/lib.rs

@@ -1838,6 +1838,11 @@ impl<'a> State<'a> {
                 self.commasep(Inconsistent, after, |s, p| s.print_pat(p));
                 self.word("]");
             }
+            PatKind::Err(_) => {
+                self.popen();
+                self.word("/*ERROR*/");
+                self.pclose();
+            }
         }
         self.ann.post(self, AnnNode::Pat(pat))
     }

compiler/rustc_hir_typeck/src/expr_use_visitor.rs

@@ -458,11 +458,15 @@ impl<'a, 'tcx> ExprUseVisitor<'a, 'tcx> {
                             needs_to_be_read = true;
                         }
                     }
-                    PatKind::Or(_) | PatKind::Box(_) | PatKind::Ref(..) | PatKind::Wild => {
+                    PatKind::Or(_)
+                    | PatKind::Box(_)
+                    | PatKind::Ref(..)
+                    | PatKind::Wild
+                    | PatKind::Err(_) => {
                         // If the PatKind is Or, Box, or Ref, the decision is made later
                         // as these patterns contains subpatterns
-                        // If the PatKind is Wild, the decision is made based on the other patterns being
-                        // examined
+                        // If the PatKind is Wild or Err, the decision is made based on the other patterns
+                        // being examined
                     }
                 }
             })?

compiler/rustc_hir_typeck/src/mem_categorization.rs

@@ -767,7 +767,8 @@ impl<'a, 'tcx> MemCategorizationContext<'a, 'tcx> {
             | PatKind::Lit(..)
             | PatKind::Range(..)
             | PatKind::Never
-            | PatKind::Wild => {
+            | PatKind::Wild
+            | PatKind::Err(_) => {
                 // always ok
             }
         }

compiler/rustc_hir_typeck/src/pat.rs

@@ -177,7 +177,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             PatInfo { binding_mode: def_bm, top_info: ti, decl_origin: pat_info.decl_origin };
 
         let ty = match pat.kind {
-            PatKind::Wild => expected,
+            PatKind::Wild | PatKind::Err(_) => expected,
             // FIXME(never_patterns): check the type is uninhabited. If that is not possible within
             // typeck, do that in a later phase.
             PatKind::Never => expected,
@@ -325,6 +325,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             PatKind::Ref(..) => AdjustMode::Reset,
             // A `_` pattern works with any expected type, so there's no need to do anything.
             PatKind::Wild
+            // A malformed pattern doesn't have an expected type, so let's just accept any type.
+            | PatKind::Err(_)
             // Bindings also work with whatever the expected type is,
             // and moreover if we peel references off, that will give us the wrong binding type.
             // Also, we can have a subpattern `binding @ pat`.
@@ -754,7 +756,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         | PatKind::Box(..)
                         | PatKind::Ref(..)
                         | PatKind::Lit(..)
-                        | PatKind::Range(..) => break 'block None,
+                        | PatKind::Range(..)
+                        | PatKind::Err(_) => break 'block None,
                     },
 
                     // Don't provide suggestions in other cases

compiler/rustc_lint/src/unused.rs

@@ -1166,7 +1166,7 @@ impl EarlyLintPass for UnusedParens {
             // Do not lint on `(..)` as that will result in the other arms being useless.
             Paren(_)
             // The other cases do not contain sub-patterns.
-            | Wild | Never | Rest | Lit(..) | MacCall(..) | Range(..) | Ident(.., None) | Path(..) => {},
+            | Wild | Never | Rest | Lit(..) | MacCall(..) | Range(..) | Ident(.., None) | Path(..) | Err(_) => {},
             // These are list-like patterns; parens can always be removed.
             TupleStruct(_, _, ps) | Tuple(ps) | Slice(ps) | Or(ps) => for p in ps {
                 self.check_unused_parens_pat(cx, p, false, false, keep_space);

compiler/rustc_mir_build/src/thir/pattern/mod.rs

@@ -345,6 +345,8 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
             }
 
             hir::PatKind::Or(pats) => PatKind::Or { pats: self.lower_patterns(pats) },
+
+            hir::PatKind::Err(guar) => PatKind::Error(guar),
         };
 
         Box::new(Pat { span, ty, kind })

compiler/rustc_passes/src/hir_stats.rs

@@ -303,7 +303,8 @@ impl<'v> hir_visit::Visitor<'v> for StatCollector<'v> {
                 Ref,
                 Lit,
                 Range,
-                Slice
+                Slice,
+                Err
             ]
         );
         hir_visit::walk_pat(self, p)
@@ -576,7 +577,8 @@ impl<'v> ast_visit::Visitor<'v> for StatCollector<'v> {
                 Rest,
                 Never,
                 Paren,
-                MacCall
+                MacCall,
+                Err
             ]
         );
         ast_visit::walk_pat(self, p)

src/librustdoc/clean/utils.rs

@@ -312,7 +312,9 @@ pub(crate) fn name_from_pat(p: &hir::Pat<'_>) -> Symbol {
 
     Symbol::intern(&match p.kind {
         // FIXME(never_patterns): does this make sense?
-        PatKind::Wild | PatKind::Never | PatKind::Struct(..) => return kw::Underscore,
+        PatKind::Wild | PatKind::Err(_) | PatKind::Never | PatKind::Struct(..) => {
+            return kw::Underscore;
+        }
         PatKind::Binding(_, _, ident, _) => return ident.name,
         PatKind::TupleStruct(ref p, ..) | PatKind::Path(ref p) => qpath_to_string(p),
         PatKind::Or(pats) => {

src/tools/clippy/clippy_lints/src/equatable_if_let.rs

@@ -51,7 +51,8 @@ fn unary_pattern(pat: &Pat<'_>) -> bool {
         | PatKind::Binding(..)
         | PatKind::Wild
         | PatKind::Never
-        | PatKind::Or(_) => false,
+        | PatKind::Or(_)
+        | PatKind::Err(_) => false,
         PatKind::Struct(_, a, etc) => !etc && a.iter().all(|x| unary_pattern(x.pat)),
         PatKind::Tuple(a, etc) | PatKind::TupleStruct(_, a, etc) => etc.as_opt_usize().is_none() && array_rec(a),
         PatKind::Ref(x, _) | PatKind::Box(x) => unary_pattern(x),

src/tools/clippy/clippy_lints/src/matches/match_same_arms.rs

@@ -11,7 +11,7 @@ use rustc_hir::{Arm, Expr, ExprKind, HirId, HirIdMap, HirIdMapEntry, HirIdSet, P
 use rustc_lint::builtin::NON_EXHAUSTIVE_OMITTED_PATTERNS;
 use rustc_lint::LateContext;
 use rustc_middle::ty;
-use rustc_span::Symbol;
+use rustc_span::{ErrorGuaranteed, Symbol};
 
 use super::MATCH_SAME_ARMS;
 
@@ -167,6 +167,8 @@ enum NormalizedPat<'a> {
     /// contains everything afterwards. Note that either side, or both sides, may contain zero
     /// patterns.
     Slice(&'a [Self], Option<&'a [Self]>),
+    /// A placeholder for a pattern that wasn't well formed in some way.
+    Err(ErrorGuaranteed),
 }
 
 #[derive(Clone, Copy)]
@@ -329,6 +331,7 @@ impl<'a> NormalizedPat<'a> {
                 arena.alloc_from_iter(front.iter().map(|pat| Self::from_pat(cx, arena, pat))),
                 wild_pat.map(|_| &*arena.alloc_from_iter(back.iter().map(|pat| Self::from_pat(cx, arena, pat)))),
             ),
+            PatKind::Err(guar) => Self::Err(guar),
         }
     }
 

src/tools/clippy/clippy_lints/src/unnested_or_patterns.rs

@@ -226,7 +226,7 @@ fn transform_with_focus_on_idx(alternatives: &mut ThinVec<P<Pat>>, focus_idx: us
         // Therefore they are not some form of constructor `C`,
         // with which a pattern `C(p_0)` may be formed,
         // which we would want to join with other `C(p_j)`s.
-        Ident(.., None) | Lit(_) | Wild | Never | Path(..) | Range(..) | Rest | MacCall(_)
+        Ident(.., None) | Lit(_) | Wild | Err(_) | Never | Path(..) | Range(..) | Rest | MacCall(_)
         // Skip immutable refs, as grouping them saves few characters,
         // and almost always requires adding parens (increasing noisiness).
         // In the case of only two patterns, replacement adds net characters.

src/tools/clippy/clippy_lints/src/utils/author.rs

@@ -710,6 +710,7 @@ impl<'a, 'tcx> PrintVisitor<'a, 'tcx> {
                 self.slice(start, |pat| self.pat(pat));
                 self.slice(end, |pat| self.pat(pat));
             },
+            PatKind::Err(_) => kind!("Err"),
         }
     }
 

src/tools/clippy/clippy_utils/src/hir_utils.rs

@@ -1007,7 +1007,7 @@ impl<'a, 'tcx> SpanlessHash<'a, 'tcx> {
                 }
                 e.hash(&mut self.s);
             },
-            PatKind::Never | PatKind::Wild => {},
+            PatKind::Never | PatKind::Wild | PatKind::Err(_) => {},
         }
     }
 

src/tools/clippy/clippy_utils/src/lib.rs

@@ -1733,6 +1733,7 @@ pub fn is_refutable(cx: &LateContext<'_>, pat: &Pat<'_>) -> bool {
                 },
             }
         },
+        PatKind::Err(_) => true,
     }
 }
 

src/tools/rustfmt/src/patterns.rs

@@ -40,9 +40,11 @@ pub(crate) fn is_short_pattern(pat: &ast::Pat, pat_str: &str) -> bool {
 
 fn is_short_pattern_inner(pat: &ast::Pat) -> bool {
     match pat.kind {
-        ast::PatKind::Rest | ast::PatKind::Never | ast::PatKind::Wild | ast::PatKind::Lit(_) => {
-            true
-        }
+        ast::PatKind::Rest
+        | ast::PatKind::Never
+        | ast::PatKind::Wild
+        | ast::PatKind::Err(_)
+        | ast::PatKind::Lit(_) => true,
         ast::PatKind::Ident(_, _, ref pat) => pat.is_none(),
         ast::PatKind::Struct(..)
         | ast::PatKind::MacCall(..)
@@ -274,6 +276,7 @@ impl Rewrite for Pat {
             PatKind::Paren(ref pat) => pat
                 .rewrite(context, shape.offset_left(1)?.sub_width(1)?)
                 .map(|inner_pat| format!("({})", inner_pat)),
+            PatKind::Err(_) => None,
         }
     }
 }