Prevent more spurious unreachable pattern lints

compiler/rustc_middle/src/thir.rs

@@ -19,11 +19,12 @@ use rustc_middle::middle::region;
 use rustc_middle::mir::interpret::AllocId;
 use rustc_middle::mir::{self, BinOp, BorrowKind, FakeReadCause, Mutability, UnOp};
 use rustc_middle::ty::adjustment::PointerCoercion;
-use rustc_middle::ty::GenericArgsRef;
-use rustc_middle::ty::{self, AdtDef, FnSig, List, Ty, UpvarArgs};
-use rustc_middle::ty::{CanonicalUserType, CanonicalUserTypeAnnotation};
+use rustc_middle::ty::{
+    self, AdtDef, CanonicalUserType, CanonicalUserTypeAnnotation, FnSig, GenericArgsRef, List, Ty,
+    UpvarArgs,
+};
 use rustc_span::def_id::LocalDefId;
-use rustc_span::{sym, Span, Symbol, DUMMY_SP};
+use rustc_span::{sym, ErrorGuaranteed, Span, Symbol, DUMMY_SP};
 use rustc_target::abi::{FieldIdx, VariantIdx};
 use rustc_target::asm::InlineAsmRegOrRegClass;
 use std::fmt;
@@ -632,7 +633,7 @@ impl<'tcx> Pat<'tcx> {
 
         use PatKind::*;
         match &self.kind {
-            Wild | Range(..) | Binding { subpattern: None, .. } | Constant { .. } => {}
+            Wild | Range(..) | Binding { subpattern: None, .. } | Constant { .. } | Error(_) => {}
             AscribeUserType { subpattern, .. }
             | Binding { subpattern: Some(subpattern), .. }
             | Deref { subpattern } => subpattern.walk_(it),
@@ -647,6 +648,21 @@ impl<'tcx> Pat<'tcx> {
         }
     }
 
+    /// Whether the pattern has a `PatKind::Error` nested within.
+    pub fn pat_error_reported(&self) -> Result<(), ErrorGuaranteed> {
+        let mut error = None;
+        self.walk(|pat| {
+            if let PatKind::Error(e) = pat.kind && error.is_none() {
+                error = Some(e);
+            }
+            error.is_none()
+        });
+        match error {
+            None => Ok(()),
+            Some(e) => Err(e),
+        }
+    }
+
     /// Walk the pattern in left-to-right order.
     ///
     /// If you always want to recurse, prefer this method over `walk`.
@@ -771,6 +787,10 @@ pub enum PatKind<'tcx> {
     Or {
         pats: Box<[Box<Pat<'tcx>>]>,
     },
+
+    /// An error has been encountered during lowering. We probably shouldn't report more lints
+    /// related to this pattern.
+    Error(ErrorGuaranteed),
 }
 
 #[derive(Clone, Debug, PartialEq, HashStable, TypeVisitable)]
@@ -934,6 +954,7 @@ impl<'tcx> fmt::Display for Pat<'tcx> {
                 }
                 Ok(())
             }
+            PatKind::Error(_) => write!(f, "<error>"),
         }
     }
 }

compiler/rustc_middle/src/thir/visit.rs

@@ -226,7 +226,7 @@ pub fn walk_pat<'a, 'tcx: 'a, V: Visitor<'a, 'tcx>>(visitor: &mut V, pat: &Pat<'
             is_primary: _,
             name: _,
         } => visitor.visit_pat(&subpattern),
-        Binding { .. } | Wild => {}
+        Binding { .. } | Wild | Error(_) => {}
         Variant { subpatterns, adt_def: _, args: _, variant_index: _ } | Leaf { subpatterns } => {
             for subpattern in subpatterns {
                 visitor.visit_pat(&subpattern.pattern);

compiler/rustc_mir_build/src/build/matches/mod.rs

@@ -814,7 +814,10 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 }
             }
 
-            PatKind::Constant { .. } | PatKind::Range { .. } | PatKind::Wild => {}
+            PatKind::Constant { .. }
+            | PatKind::Range { .. }
+            | PatKind::Wild
+            | PatKind::Error(_) => {}
 
             PatKind::Deref { ref subpattern } => {
                 self.visit_primary_bindings(subpattern, pattern_user_ty.deref(), f);

compiler/rustc_mir_build/src/build/matches/simplify.rs

@@ -168,7 +168,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 Ok(())
             }
 
-            PatKind::Wild => {
+            PatKind::Wild | PatKind::Error(_) => {
                 // nothing left to do
                 Ok(())
             }

compiler/rustc_mir_build/src/build/matches/test.rs

@@ -77,7 +77,8 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             | PatKind::Wild
             | PatKind::Binding { .. }
             | PatKind::Leaf { .. }
-            | PatKind::Deref { .. } => self.error_simplifiable(match_pair),
+            | PatKind::Deref { .. }
+            | PatKind::Error(_) => self.error_simplifiable(match_pair),
         }
     }
 
@@ -111,7 +112,8 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             | PatKind::Binding { .. }
             | PatKind::AscribeUserType { .. }
             | PatKind::Leaf { .. }
-            | PatKind::Deref { .. } => {
+            | PatKind::Deref { .. }
+            | PatKind::Error(_) => {
                 // don't know how to add these patterns to a switch
                 false
             }

compiler/rustc_mir_build/src/check_unsafety.rs

@@ -224,7 +224,8 @@ impl<'a, 'tcx> Visitor<'a, 'tcx> for UnsafetyVisitor<'a, 'tcx> {
                 PatKind::Wild |
                 // these just wrap other patterns
                 PatKind::Or { .. } |
-                PatKind::AscribeUserType { .. } => {}
+                PatKind::AscribeUserType { .. } |
+                PatKind::Error(_) => {}
             }
         };
 

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

@@ -19,7 +19,7 @@ use rustc_hir::HirId;
 use rustc_middle::thir::visit::{self, Visitor};
 use rustc_middle::thir::*;
 use rustc_middle::ty::print::with_no_trimmed_paths;
-use rustc_middle::ty::{self, AdtDef, Ty, TyCtxt, TypeVisitableExt};
+use rustc_middle::ty::{self, AdtDef, Ty, TyCtxt};
 use rustc_session::lint::builtin::{
     BINDINGS_WITH_VARIANT_NAME, IRREFUTABLE_LET_PATTERNS, UNREACHABLE_PATTERNS,
 };
@@ -231,6 +231,10 @@ impl<'p, 'tcx> MatchVisitor<'_, 'p, 'tcx> {
         if let LetSource::None = source {
             return;
         }
+        if let Err(err) = pat.pat_error_reported() {
+            self.error = Err(err);
+            return;
+        }
         self.check_patterns(pat, Refutable);
         let mut cx = self.new_cx(self.lint_level, true);
         let tpat = self.lower_pattern(&mut cx, pat);
@@ -252,6 +256,10 @@ impl<'p, 'tcx> MatchVisitor<'_, 'p, 'tcx> {
             self.with_lint_level(arm.lint_level, |this| {
                 this.check_patterns(&arm.pattern, Refutable);
             });
+            if let Err(err) = arm.pattern.pat_error_reported() {
+                self.error = Err(err);
+                return;
+            }
         }
 
         let tarms: Vec<_> = arms
@@ -334,7 +342,8 @@ impl<'p, 'tcx> MatchVisitor<'_, 'p, 'tcx> {
         // and record chain members that aren't let exprs.
         let mut chain_refutabilities = Vec::new();
 
-        let add = |expr: ExprId, mut local_lint_level| {
+        let mut error = Ok(());
+        let mut add = |expr: ExprId, mut local_lint_level| {
             // `local_lint_level` is the lint level enclosing the pattern inside `expr`.
             let mut expr = &self.thir[expr];
             debug!(?expr, ?local_lint_level, "add");
@@ -348,6 +357,10 @@ impl<'p, 'tcx> MatchVisitor<'_, 'p, 'tcx> {
             debug!(?expr, ?local_lint_level, "after scopes");
             match expr.kind {
                 ExprKind::Let { box ref pat, expr: _ } => {
+                    if let Err(err) = pat.pat_error_reported() {
+                        error = Err(err);
+                        return None;
+                    }
                     let mut ncx = self.new_cx(local_lint_level, true);
                     let tpat = self.lower_pattern(&mut ncx, pat);
                     let refutable = !is_let_irrefutable(&mut ncx, local_lint_level, tpat);
@@ -380,6 +393,11 @@ impl<'p, 'tcx> MatchVisitor<'_, 'p, 'tcx> {
         debug!(?chain_refutabilities);
         chain_refutabilities.reverse();
 
+        if error.is_err() {
+            self.error = error;
+            return;
+        }
+
         // Third, emit the actual warnings.
         if chain_refutabilities.iter().all(|r| matches!(*r, Some((_, false)))) {
             // The entire chain is made up of irrefutable `let` statements
@@ -426,6 +444,12 @@ impl<'p, 'tcx> MatchVisitor<'_, 'p, 'tcx> {
 
     #[instrument(level = "trace", skip(self))]
     fn check_irrefutable(&mut self, pat: &Pat<'tcx>, origin: &str, sp: Option<Span>) {
+        // If we got errors while lowering, don't emit anything more.
+        if let Err(err) = pat.pat_error_reported() {
+            self.error = Err(err);
+            return;
+        }
+
         let mut cx = self.new_cx(self.lint_level, false);
 
         let pattern = self.lower_pattern(&mut cx, pat);
@@ -682,12 +706,6 @@ fn non_exhaustive_match<'p, 'tcx>(
     arms: &[ArmId],
     expr_span: Span,
 ) -> ErrorGuaranteed {
-    for &arm in arms {
-        if let Err(err) = thir[arm].pattern.error_reported() {
-            return err;
-        }
-    }
-
     let is_empty_match = arms.is_empty();
     let non_empty_enum = match scrut_ty.kind() {
         ty::Adt(def, _) => def.is_enum() && !def.variants().is_empty(),

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

@@ -196,9 +196,7 @@ impl<'tcx> ConstToPat<'tcx> {
                     };
                     // All branches above emitted an error. Don't print any more lints.
                     // We errored. Signal that in the pattern, so that follow up errors can be silenced.
-                    let kind = PatKind::Constant {
-                        value: mir::Const::Ty(ty::Const::new_error(self.tcx(), e, cv.ty())),
-                    };
+                    let kind = PatKind::Error(e);
                     return Box::new(Pat { span: self.span, ty: cv.ty(), kind });
                 } else if !self.saw_const_match_lint.get() {
                     if let Some(mir_structural_match_violation) = mir_structural_match_violation {
@@ -351,15 +349,15 @@ impl<'tcx> ConstToPat<'tcx> {
                 let e = tcx.sess.emit_err(InvalidPattern { span, non_sm_ty: ty });
                 self.saw_const_match_error.set(Some(e));
                 // We errored. Signal that in the pattern, so that follow up errors can be silenced.
-                PatKind::Constant { value: mir::Const::Ty(ty::Const::new_error(tcx, e, ty)) }
+                PatKind::Error(e)
             }
             ty::Adt(adt_def, _) if !self.type_marked_structural(ty) => {
                 debug!("adt_def {:?} has !type_marked_structural for cv.ty: {:?}", adt_def, ty,);
                 let err = TypeNotStructural { span, non_sm_ty: ty };
                 let e = tcx.sess.emit_err(err);
                 self.saw_const_match_error.set(Some(e));
                 // We errored. Signal that in the pattern, so that follow up errors can be silenced.
-                PatKind::Constant { value: mir::Const::Ty(ty::Const::new_error(tcx, e, ty)) }
+                PatKind::Error(e)
             }
             ty::Adt(adt_def, args) if adt_def.is_enum() => {
                 let (&variant_index, fields) = cv.unwrap_branch().split_first().unwrap();
@@ -434,17 +432,13 @@ impl<'tcx> ConstToPat<'tcx> {
                     } else {
                         if let Some(e) = self.saw_const_match_error.get() {
                             // We already errored. Signal that in the pattern, so that follow up errors can be silenced.
-                            PatKind::Constant {
-                                value: mir::Const::Ty(ty::Const::new_error(tcx, e, ty)),
-                            }
+                            PatKind::Error(e)
                         } else {
                             let err = TypeNotStructural { span, non_sm_ty: *pointee_ty };
                             let e = tcx.sess.emit_err(err);
                             self.saw_const_match_error.set(Some(e));
                             // We errored. Signal that in the pattern, so that follow up errors can be silenced.
-                            PatKind::Constant {
-                                value: mir::Const::Ty(ty::Const::new_error(tcx, e, ty)),
-                            }
+                            PatKind::Error(e)
                         }
                     }
                 }
@@ -456,9 +450,7 @@ impl<'tcx> ConstToPat<'tcx> {
                         let err = UnsizedPattern { span, non_sm_ty: *pointee_ty };
                         let e = tcx.sess.emit_err(err);
                         // We errored. Signal that in the pattern, so that follow up errors can be silenced.
-                        PatKind::Constant {
-                            value: mir::Const::Ty(ty::Const::new_error(tcx, e, ty)),
-                        }
+                        PatKind::Error(e)
                     } else {
                         let old = self.behind_reference.replace(true);
                         // `b"foo"` produces a `&[u8; 3]`, but you can't use constants of array type when
@@ -489,7 +481,7 @@ impl<'tcx> ConstToPat<'tcx> {
                 let e = tcx.sess.emit_err(err);
                 self.saw_const_match_error.set(Some(e));
                 // We errored. Signal that in the pattern, so that follow up errors can be silenced.
-                PatKind::Constant { value: mir::Const::Ty(ty::Const::new_error(tcx, e, ty)) }
+                PatKind::Error(e)
             }
         };
 

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

@@ -1525,6 +1525,10 @@ impl<'p, 'tcx> DeconstructedPat<'p, 'tcx> {
                 let pats = expand_or_pat(pat);
                 fields = Fields::from_iter(cx, pats.into_iter().map(mkpat));
             }
+            PatKind::Error(_) => {
+                ctor = Opaque;
+                fields = Fields::empty();
+            }
         }
         DeconstructedPat::new(ctor, fields, pat.ty, pat.span)
     }