Merging upstream version 1.74.1+dfsg1.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 56 insertions, 31 deletions

diff --git a/compiler/rustc_mir_build/src/thir/pattern/const_to_pat.rs b/compiler/rustc_mir_build/src/thir/pattern/const_to_pat.rs
index 1376344cf..ae4424660 100644
--- a/compiler/rustc_mir_build/src/thir/pattern/const_to_pat.rs
+++ b/compiler/rustc_mir_build/src/thir/pattern/const_to_pat.rs
@@ -16,18 +16,20 @@ use std::cell::Cell;
 
 use super::PatCtxt;
 use crate::errors::{
-    FloatPattern, IndirectStructuralMatch, InvalidPattern, NontrivialStructuralMatch,
-    PointerPattern, TypeNotStructural, UnionPattern, UnsizedPattern,
+    FloatPattern, IndirectStructuralMatch, InvalidPattern, NonPartialEqMatch,
+    NontrivialStructuralMatch, PointerPattern, TypeNotStructural, UnionPattern, UnsizedPattern,
 };
 
 impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
     /// Converts an evaluated constant to a pattern (if possible).
     /// This means aggregate values (like structs and enums) are converted
     /// to a pattern that matches the value (as if you'd compared via structural equality).
+    ///
+    /// `cv` must be a valtree or a `mir::ConstValue`.
     #[instrument(level = "debug", skip(self), ret)]
     pub(super) fn const_to_pat(
         &self,
-        cv: mir::ConstantKind<'tcx>,
+        cv: mir::Const<'tcx>,
         id: hir::HirId,
         span: Span,
         check_body_for_struct_match_violation: Option<DefId>,
@@ -64,12 +66,10 @@ struct ConstToPat<'tcx> {
 }
 
 /// This error type signals that we encountered a non-struct-eq situation.
-/// We bubble this up in order to get back to the reference destructuring and make that emit
-/// a const pattern instead of a deref pattern. This allows us to simply call `PartialEq::eq`
-/// on such patterns (since that function takes a reference) and not have to jump through any
-/// hoops to get a reference to the value.
+/// We will fall back to calling `PartialEq::eq` on such patterns,
+/// and exhaustiveness checking will consider them as matching nothing.
 #[derive(Debug)]
-struct FallbackToConstRef;
+struct FallbackToOpaqueConst;
 
 impl<'tcx> ConstToPat<'tcx> {
     fn new(
@@ -104,7 +104,7 @@ impl<'tcx> ConstToPat<'tcx> {
 
     fn to_pat(
         &mut self,
-        cv: mir::ConstantKind<'tcx>,
+        cv: mir::Const<'tcx>,
         check_body_for_struct_match_violation: Option<DefId>,
     ) -> Box<Pat<'tcx>> {
         trace!(self.treat_byte_string_as_slice);
@@ -124,7 +124,7 @@ impl<'tcx> ConstToPat<'tcx> {
         debug!(?check_body_for_struct_match_violation, ?mir_structural_match_violation);
 
         let inlined_const_as_pat = match cv {
-            mir::ConstantKind::Ty(c) => match c.kind() {
+            mir::Const::Ty(c) => match c.kind() {
                 ty::ConstKind::Param(_)
                 | ty::ConstKind::Infer(_)
                 | ty::ConstKind::Bound(_, _)
@@ -136,7 +136,7 @@ impl<'tcx> ConstToPat<'tcx> {
                 }
                 ty::ConstKind::Value(valtree) => self
                     .recur(valtree, cv.ty(), mir_structural_match_violation.unwrap_or(false))
-                    .unwrap_or_else(|_| {
+                    .unwrap_or_else(|_: FallbackToOpaqueConst| {
                         Box::new(Pat {
                             span: self.span,
                             ty: cv.ty(),
@@ -144,10 +144,10 @@ impl<'tcx> ConstToPat<'tcx> {
                         })
                     }),
             },
-            mir::ConstantKind::Unevaluated(_, _) => {
+            mir::Const::Unevaluated(_, _) => {
                 span_bug!(self.span, "unevaluated const in `to_pat`: {cv:?}")
             }
-            mir::ConstantKind::Val(_, _) => Box::new(Pat {
+            mir::Const::Val(_, _) => Box::new(Pat {
                 span: self.span,
                 ty: cv.ty(),
                 kind: PatKind::Constant { value: cv },
@@ -155,8 +155,9 @@ impl<'tcx> ConstToPat<'tcx> {
         };
 
         if !self.saw_const_match_error.get() {
-            // If we were able to successfully convert the const to some pat,
-            // double-check that all types in the const implement `Structural`.
+            // If we were able to successfully convert the const to some pat (possibly with some
+            // lints, but no errors), double-check that all types in the const implement
+            // `Structural` and `PartialEq`.
 
             let structural =
                 traits::search_for_structural_match_violation(self.span, self.tcx(), cv.ty());
@@ -178,7 +179,7 @@ impl<'tcx> ConstToPat<'tcx> {
             }
 
             if let Some(non_sm_ty) = structural {
-                if !self.type_may_have_partial_eq_impl(cv.ty()) {
+                if !self.type_has_partial_eq_impl(cv.ty()) {
                     if let ty::Adt(def, ..) = non_sm_ty.kind() {
                         if def.is_union() {
                             let err = UnionPattern { span: self.span };
@@ -192,8 +193,10 @@ impl<'tcx> ConstToPat<'tcx> {
                     } else {
                         let err = InvalidPattern { span: self.span, non_sm_ty };
                         self.tcx().sess.emit_err(err);
-                        return Box::new(Pat { span: self.span, ty: cv.ty(), kind: PatKind::Wild });
                     }
+                    // All branches above emitted an error. Don't print any more lints.
+                    // The pattern we return is irrelevant since we errored.
+                    return Box::new(Pat { span: self.span, ty: cv.ty(), kind: PatKind::Wild });
                 } else if !self.saw_const_match_lint.get() {
                     if let Some(mir_structural_match_violation) = mir_structural_match_violation {
                         match non_sm_ty.kind() {
@@ -238,13 +241,24 @@ impl<'tcx> ConstToPat<'tcx> {
                     _ => {}
                 }
             }
+
+            // Always check for `PartialEq`, even if we emitted other lints. (But not if there were
+            // any errors.) This ensures it shows up in cargo's future-compat reports as well.
+            if !self.type_has_partial_eq_impl(cv.ty()) {
+                self.tcx().emit_spanned_lint(
+                    lint::builtin::CONST_PATTERNS_WITHOUT_PARTIAL_EQ,
+                    self.id,
+                    self.span,
+                    NonPartialEqMatch { non_peq_ty: cv.ty() },
+                );
+            }
         }
 
         inlined_const_as_pat
     }
 
     #[instrument(level = "trace", skip(self), ret)]
-    fn type_may_have_partial_eq_impl(&self, ty: Ty<'tcx>) -> bool {
+    fn type_has_partial_eq_impl(&self, ty: Ty<'tcx>) -> bool {
         // double-check there even *is* a semantic `PartialEq` to dispatch to.
         //
         // (If there isn't, then we can safely issue a hard
@@ -259,14 +273,19 @@ impl<'tcx> ConstToPat<'tcx> {
             ty::TraitRef::new(self.tcx(), partial_eq_trait_id, [ty, ty]),
         );
 
-        // FIXME: should this call a `predicate_must_hold` variant instead?
-        self.infcx.predicate_may_hold(&partial_eq_obligation)
+        // This *could* accept a type that isn't actually `PartialEq`, because region bounds get
+        // ignored. However that should be pretty much impossible since consts that do not depend on
+        // generics can only mention the `'static` lifetime, and how would one have a type that's
+        // `PartialEq` for some lifetime but *not* for `'static`? If this ever becomes a problem
+        // we'll need to leave some sort of trace of this requirement in the MIR so that borrowck
+        // can ensure that the type really implements `PartialEq`.
+        self.infcx.predicate_must_hold_modulo_regions(&partial_eq_obligation)
     }
 
     fn field_pats(
         &self,
         vals: impl Iterator<Item = (ValTree<'tcx>, Ty<'tcx>)>,
-    ) -> Result<Vec<FieldPat<'tcx>>, FallbackToConstRef> {
+    ) -> Result<Vec<FieldPat<'tcx>>, FallbackToOpaqueConst> {
         vals.enumerate()
             .map(|(idx, (val, ty))| {
                 let field = FieldIdx::new(idx);
@@ -284,7 +303,7 @@ impl<'tcx> ConstToPat<'tcx> {
         cv: ValTree<'tcx>,
         ty: Ty<'tcx>,
         mir_structural_match_violation: bool,
-    ) -> Result<Box<Pat<'tcx>>, FallbackToConstRef> {
+    ) -> Result<Box<Pat<'tcx>>, FallbackToOpaqueConst> {
         let id = self.id;
         let span = self.span;
         let tcx = self.tcx();
@@ -299,7 +318,7 @@ impl<'tcx> ConstToPat<'tcx> {
                     span,
                     FloatPattern,
                 );
-                return Err(FallbackToConstRef);
+                return Err(FallbackToOpaqueConst);
             }
             // If the type is not structurally comparable, just emit the constant directly,
             // causing the pattern match code to treat it opaquely.
@@ -323,11 +342,12 @@ impl<'tcx> ConstToPat<'tcx> {
                 // Since we are behind a reference, we can just bubble the error up so we get a
                 // constant at reference type, making it easy to let the fallback call
                 // `PartialEq::eq` on it.
-                return Err(FallbackToConstRef);
+                return Err(FallbackToOpaqueConst);
             }
             ty::FnDef(..) => {
                 self.saw_const_match_error.set(true);
                 tcx.sess.emit_err(InvalidPattern { span, non_sm_ty: ty });
+                // We errored, so the pattern we generate is irrelevant.
                 PatKind::Wild
             }
             ty::Adt(adt_def, _) if !self.type_marked_structural(ty) => {
@@ -335,6 +355,7 @@ impl<'tcx> ConstToPat<'tcx> {
                 self.saw_const_match_error.set(true);
                 let err = TypeNotStructural { span, non_sm_ty: ty };
                 tcx.sess.emit_err(err);
+                // We errored, so the pattern we generate is irrelevant.
                 PatKind::Wild
             }
             ty::Adt(adt_def, args) if adt_def.is_enum() => {
@@ -385,9 +406,9 @@ impl<'tcx> ConstToPat<'tcx> {
             ty::Ref(_, pointee_ty, ..) => match *pointee_ty.kind() {
                 // `&str` is represented as a valtree, let's keep using this
                 // optimization for now.
-                ty::Str => PatKind::Constant {
-                    value: mir::ConstantKind::Ty(ty::Const::new_value(tcx, cv, ty)),
-                },
+                ty::Str => {
+                    PatKind::Constant { value: mir::Const::Ty(ty::Const::new_value(tcx, cv, ty)) }
+                }
                 // Backwards compatibility hack: support references to non-structural types,
                 // but hard error if we aren't behind a double reference. We could just use
                 // the fallback code path below, but that would allow *more* of this fishy
@@ -404,13 +425,15 @@ impl<'tcx> ConstToPat<'tcx> {
                                 IndirectStructuralMatch { non_sm_ty: *pointee_ty },
                             );
                         }
-                        return Err(FallbackToConstRef);
+                        return Err(FallbackToOpaqueConst);
                     } else {
                         if !self.saw_const_match_error.get() {
                             self.saw_const_match_error.set(true);
                             let err = TypeNotStructural { span, non_sm_ty: *pointee_ty };
                             tcx.sess.emit_err(err);
                         }
+                        tcx.sess.delay_span_bug(span, "`saw_const_match_error` set but no error?");
+                        // We errored, so the pattern we generate is irrelevant.
                         PatKind::Wild
                     }
                 }
@@ -423,6 +446,7 @@ impl<'tcx> ConstToPat<'tcx> {
                         tcx.sess.emit_err(err);
 
                         // FIXME: introduce PatKind::Error to silence follow up diagnostics due to unreachable patterns.
+                        // We errored, so the pattern we generate is irrelevant.
                         PatKind::Wild
                     } else {
                         let old = self.behind_reference.replace(true);
@@ -445,14 +469,15 @@ impl<'tcx> ConstToPat<'tcx> {
                     }
                 }
             },
-            ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) => PatKind::Constant {
-                value: mir::ConstantKind::Ty(ty::Const::new_value(tcx, cv, ty)),
-            },
+            ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) => {
+                PatKind::Constant { value: mir::Const::Ty(ty::Const::new_value(tcx, cv, ty)) }
+            }
             ty::FnPtr(..) | ty::RawPtr(..) => unreachable!(),
             _ => {
                 self.saw_const_match_error.set(true);
                 let err = InvalidPattern { span, non_sm_ty: ty };
                 tcx.sess.emit_err(err);
+                // We errored, so the pattern we generate is irrelevant.
                 PatKind::Wild
             }
         };