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

   1 use rustc_hir as hir;
   2 use rustc_index::vec::Idx;
   3 use rustc_infer::infer::{InferCtxt, TyCtxtInferExt};
   4 use rustc_middle::mir::{self, Field};
   5 use rustc_middle::thir::{FieldPat, Pat, PatKind};
   6 use rustc_middle::ty::print::with_no_trimmed_paths;
   7 use rustc_middle::ty::{self, AdtDef, Ty, TyCtxt};
   8 use rustc_session::lint;
   9 use rustc_span::Span;
  10 use rustc_trait_selection::traits::predicate_for_trait_def;
  11 use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt;
  12 use rustc_trait_selection::traits::{self, ObligationCause, PredicateObligation};
  13
  14 use std::cell::Cell;
  15
  16 use super::PatCtxt;
  17
  18 impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
  19     /// Converts an evaluated constant to a pattern (if possible).
  20     /// This means aggregate values (like structs and enums) are converted
  21     /// to a pattern that matches the value (as if you'd compared via structural equality).
  22     #[instrument(level = "debug", skip(self))]
  23     pub(super) fn const_to_pat(
  24         &self,
  25         cv: mir::ConstantKind<'tcx>,
  26         id: hir::HirId,
  27         span: Span,
  28         mir_structural_match_violation: bool,
  29     ) -> Pat<'tcx> {
  30         let pat = self.tcx.infer_ctxt().enter(|infcx| {
  31             let mut convert = ConstToPat::new(self, id, span, infcx);
  32             convert.to_pat(cv, mir_structural_match_violation)
  33         });
  34
  35         debug!(?pat);
  36         pat
  37     }
  38 }
  39
  40 struct ConstToPat<'a, 'tcx> {
  41     id: hir::HirId,
  42     span: Span,
  43     param_env: ty::ParamEnv<'tcx>,
  44
  45     // This tracks if we emitted some hard error for a given const value, so that
  46     // we will not subsequently issue an irrelevant lint for the same const
  47     // value.
  48     saw_const_match_error: Cell<bool>,
  49
  50     // This tracks if we emitted some diagnostic for a given const value, so that
  51     // we will not subsequently issue an irrelevant lint for the same const
  52     // value.
  53     saw_const_match_lint: Cell<bool>,
  54
  55     // For backcompat we need to keep allowing non-structurally-eq types behind references.
  56     // See also all the `cant-hide-behind` tests.
  57     behind_reference: Cell<bool>,
  58
  59     // inference context used for checking `T: Structural` bounds.
  60     infcx: InferCtxt<'a, 'tcx>,
  61
  62     include_lint_checks: bool,
  63
  64     treat_byte_string_as_slice: bool,
  65 }
  66
  67 mod fallback_to_const_ref {
  68     #[derive(Debug)]
  69     /// This error type signals that we encountered a non-struct-eq situation behind a reference.
  70     /// We bubble this up in order to get back to the reference destructuring and make that emit
  71     /// a const pattern instead of a deref pattern. This allows us to simply call `PartialEq::eq`
  72     /// on such patterns (since that function takes a reference) and not have to jump through any
  73     /// hoops to get a reference to the value.
  74     pub(super) struct FallbackToConstRef(());
  75
  76     pub(super) fn fallback_to_const_ref<'a, 'tcx>(
  77         c2p: &super::ConstToPat<'a, 'tcx>,
  78     ) -> FallbackToConstRef {
  79         assert!(c2p.behind_reference.get());
  80         FallbackToConstRef(())
  81     }
  82 }
  83 use fallback_to_const_ref::{fallback_to_const_ref, FallbackToConstRef};
  84
  85 impl<'a, 'tcx> ConstToPat<'a, 'tcx> {
  86     fn new(
  87         pat_ctxt: &PatCtxt<'_, 'tcx>,
  88         id: hir::HirId,
  89         span: Span,
  90         infcx: InferCtxt<'a, 'tcx>,
  91     ) -> Self {
  92         trace!(?pat_ctxt.typeck_results.hir_owner);
  93         ConstToPat {
  94             id,
  95             span,
  96             infcx,
  97             param_env: pat_ctxt.param_env,
  98             include_lint_checks: pat_ctxt.include_lint_checks,
  99             saw_const_match_error: Cell::new(false),
 100             saw_const_match_lint: Cell::new(false),
 101             behind_reference: Cell::new(false),
 102             treat_byte_string_as_slice: pat_ctxt
 103                 .typeck_results
 104                 .treat_byte_string_as_slice
 105                 .contains(&id.local_id),
 106         }
 107     }
 108
 109     fn tcx(&self) -> TyCtxt<'tcx> {
 110         self.infcx.tcx
 111     }
 112
 113     fn adt_derive_msg(&self, adt_def: AdtDef<'tcx>) -> String {
 114         let path = self.tcx().def_path_str(adt_def.did());
 115         format!(
 116             "to use a constant of type `{}` in a pattern, \
 117             `{}` must be annotated with `#[derive(PartialEq, Eq)]`",
 118             path, path,
 119         )
 120     }
 121
 122     fn search_for_structural_match_violation(&self, ty: Ty<'tcx>) -> Option<String> {
 123         traits::search_for_structural_match_violation(self.span, self.tcx(), ty).map(|non_sm_ty| {
 124             with_no_trimmed_paths!(match non_sm_ty.kind() {
 125                 ty::Adt(adt, _) => self.adt_derive_msg(*adt),
 126                 ty::Dynamic(..) => {
 127                     "trait objects cannot be used in patterns".to_string()
 128                 }
 129                 ty::Opaque(..) => {
 130                     "opaque types cannot be used in patterns".to_string()
 131                 }
 132                 ty::Closure(..) => {
 133                     "closures cannot be used in patterns".to_string()
 134                 }
 135                 ty::Generator(..) | ty::GeneratorWitness(..) => {
 136                     "generators cannot be used in patterns".to_string()
 137                 }
 138                 ty::Float(..) => {
 139                     "floating-point numbers cannot be used in patterns".to_string()
 140                 }
 141                 ty::FnPtr(..) => {
 142                     "function pointers cannot be used in patterns".to_string()
 143                 }
 144                 ty::RawPtr(..) => {
 145                     "raw pointers cannot be used in patterns".to_string()
 146                 }
 147                 _ => {
 148                     bug!("use of a value of `{non_sm_ty}` inside a pattern")
 149                 }
 150             })
 151         })
 152     }
 153
 154     fn type_marked_structural(&self, ty: Ty<'tcx>) -> bool {
 155         ty.is_structural_eq_shallow(self.infcx.tcx)
 156     }
 157
 158     fn to_pat(
 159         &mut self,
 160         cv: mir::ConstantKind<'tcx>,
 161         mir_structural_match_violation: bool,
 162     ) -> Pat<'tcx> {
 163         trace!(self.treat_byte_string_as_slice);
 164         // This method is just a wrapper handling a validity check; the heavy lifting is
 165         // performed by the recursive `recur` method, which is not meant to be
 166         // invoked except by this method.
 167         //
 168         // once indirect_structural_match is a full fledged error, this
 169         // level of indirection can be eliminated
 170
 171         let inlined_const_as_pat =
 172             self.recur(cv, mir_structural_match_violation).unwrap_or_else(|_| Pat {
 173                 span: self.span,
 174                 ty: cv.ty(),
 175                 kind: Box::new(PatKind::Constant { value: cv }),
 176             });
 177
 178         if self.include_lint_checks && !self.saw_const_match_error.get() {
 179             // If we were able to successfully convert the const to some pat,
 180             // double-check that all types in the const implement `Structural`.
 181
 182             let structural = self.search_for_structural_match_violation(cv.ty());
 183             debug!(
 184                 "search_for_structural_match_violation cv.ty: {:?} returned: {:?}",
 185                 cv.ty(),
 186                 structural
 187             );
 188
 189             // This can occur because const qualification treats all associated constants as
 190             // opaque, whereas `search_for_structural_match_violation` tries to monomorphize them
 191             // before it runs.
 192             //
 193             // FIXME(#73448): Find a way to bring const qualification into parity with
 194             // `search_for_structural_match_violation`.
 195             if structural.is_none() && mir_structural_match_violation {
 196                 warn!("MIR const-checker found novel structural match violation. See #73448.");
 197                 return inlined_const_as_pat;
 198             }
 199
 200             if let Some(msg) = structural {
 201                 if !self.type_may_have_partial_eq_impl(cv.ty()) {
 202                     // span_fatal avoids ICE from resolution of non-existent method (rare case).
 203                     self.tcx().sess.span_fatal(self.span, &msg);
 204                 } else if mir_structural_match_violation && !self.saw_const_match_lint.get() {
 205                     self.tcx().struct_span_lint_hir(
 206                         lint::builtin::INDIRECT_STRUCTURAL_MATCH,
 207                         self.id,
 208                         self.span,
 209                         |lint| {
 210                             lint.build(&msg).emit();
 211                         },
 212                     );
 213                 } else {
 214                     debug!(
 215                         "`search_for_structural_match_violation` found one, but `CustomEq` was \
 216                           not in the qualifs for that `const`"
 217                     );
 218                 }
 219             }
 220         }
 221
 222         inlined_const_as_pat
 223     }
 224
 225     fn type_may_have_partial_eq_impl(&self, ty: Ty<'tcx>) -> bool {
 226         // double-check there even *is* a semantic `PartialEq` to dispatch to.
 227         //
 228         // (If there isn't, then we can safely issue a hard
 229         // error, because that's never worked, due to compiler
 230         // using `PartialEq::eq` in this scenario in the past.)
 231         let partial_eq_trait_id =
 232             self.tcx().require_lang_item(hir::LangItem::PartialEq, Some(self.span));
 233         let obligation: PredicateObligation<'_> = predicate_for_trait_def(
 234             self.tcx(),
 235             self.param_env,
 236             ObligationCause::misc(self.span, self.id),
 237             partial_eq_trait_id,
 238             0,
 239             ty,
 240             &[],
 241         );
 242         // FIXME: should this call a `predicate_must_hold` variant instead?
 243
 244         let has_impl = self.infcx.predicate_may_hold(&obligation);
 245
 246         // Note: To fix rust-lang/rust#65466, we could just remove this type
 247         // walk hack for function pointers, and unconditionally error
 248         // if `PartialEq` is not implemented. However, that breaks stable
 249         // code at the moment, because types like `for <'a> fn(&'a ())` do
 250         // not *yet* implement `PartialEq`. So for now we leave this here.
 251         has_impl
 252             || ty.walk().any(|t| match t.unpack() {
 253                 ty::subst::GenericArgKind::Lifetime(_) => false,
 254                 ty::subst::GenericArgKind::Type(t) => t.is_fn_ptr(),
 255                 ty::subst::GenericArgKind::Const(_) => false,
 256             })
 257     }
 258
 259     fn field_pats(
 260         &self,
 261         vals: impl Iterator<Item = mir::ConstantKind<'tcx>>,
 262     ) -> Result<Vec<FieldPat<'tcx>>, FallbackToConstRef> {
 263         vals.enumerate()
 264             .map(|(idx, val)| {
 265                 let field = Field::new(idx);
 266                 Ok(FieldPat { field, pattern: self.recur(val, false)? })
 267             })
 268             .collect()
 269     }
 270
 271     // Recursive helper for `to_pat`; invoke that (instead of calling this directly).
 272     #[instrument(skip(self), level = "debug")]
 273     fn recur(
 274         &self,
 275         cv: mir::ConstantKind<'tcx>,
 276         mir_structural_match_violation: bool,
 277     ) -> Result<Pat<'tcx>, FallbackToConstRef> {
 278         let id = self.id;
 279         let span = self.span;
 280         let tcx = self.tcx();
 281         let param_env = self.param_env;
 282
 283         let kind = match cv.ty().kind() {
 284             ty::Float(_) => {
 285                 if self.include_lint_checks {
 286                     tcx.struct_span_lint_hir(
 287                         lint::builtin::ILLEGAL_FLOATING_POINT_LITERAL_PATTERN,
 288                         id,
 289                         span,
 290                         |lint| {
 291                             lint.build("floating-point types cannot be used in patterns").emit();
 292                         },
 293                     );
 294                 }
 295                 PatKind::Constant { value: cv }
 296             }
 297             ty::Adt(adt_def, _) if adt_def.is_union() => {
 298                 // Matching on union fields is unsafe, we can't hide it in constants
 299                 self.saw_const_match_error.set(true);
 300                 let msg = "cannot use unions in constant patterns";
 301                 if self.include_lint_checks {
 302                     tcx.sess.span_err(span, msg);
 303                 } else {
 304                     tcx.sess.delay_span_bug(span, msg);
 305                 }
 306                 PatKind::Wild
 307             }
 308             ty::Adt(..)
 309                 if !self.type_may_have_partial_eq_impl(cv.ty())
 310                     // FIXME(#73448): Find a way to bring const qualification into parity with
 311                     // `search_for_structural_match_violation` and then remove this condition.
 312                     && self.search_for_structural_match_violation(cv.ty()).is_some() =>
 313             {
 314                 // Obtain the actual type that isn't annotated. If we just looked at `cv.ty` we
 315                 // could get `Option<NonStructEq>`, even though `Option` is annotated with derive.
 316                 let msg = self.search_for_structural_match_violation(cv.ty()).unwrap();
 317                 self.saw_const_match_error.set(true);
 318                 if self.include_lint_checks {
 319                     tcx.sess.span_err(self.span, &msg);
 320                 } else {
 321                     tcx.sess.delay_span_bug(self.span, &msg);
 322                 }
 323                 PatKind::Wild
 324             }
 325             // If the type is not structurally comparable, just emit the constant directly,
 326             // causing the pattern match code to treat it opaquely.
 327             // FIXME: This code doesn't emit errors itself, the caller emits the errors.
 328             // So instead of specific errors, you just get blanket errors about the whole
 329             // const type. See
 330             // https://github.com/rust-lang/rust/pull/70743#discussion_r404701963 for
 331             // details.
 332             // Backwards compatibility hack because we can't cause hard errors on these
 333             // types, so we compare them via `PartialEq::eq` at runtime.
 334             ty::Adt(..) if !self.type_marked_structural(cv.ty()) && self.behind_reference.get() => {
 335                 if self.include_lint_checks
 336                     && !self.saw_const_match_error.get()
 337                     && !self.saw_const_match_lint.get()
 338                 {
 339                     self.saw_const_match_lint.set(true);
 340                     tcx.struct_span_lint_hir(
 341                         lint::builtin::INDIRECT_STRUCTURAL_MATCH,
 342                         id,
 343                         span,
 344                         |lint| {
 345                             let msg = format!(
 346                                 "to use a constant of type `{}` in a pattern, \
 347                                  `{}` must be annotated with `#[derive(PartialEq, Eq)]`",
 348                                 cv.ty(),
 349                                 cv.ty(),
 350                             );
 351                             lint.build(&msg).emit();
 352                         },
 353                     );
 354                 }
 355                 // Since we are behind a reference, we can just bubble the error up so we get a
 356                 // constant at reference type, making it easy to let the fallback call
 357                 // `PartialEq::eq` on it.
 358                 return Err(fallback_to_const_ref(self));
 359             }
 360             ty::Adt(adt_def, _) if !self.type_marked_structural(cv.ty()) => {
 361                 debug!(
 362                     "adt_def {:?} has !type_marked_structural for cv.ty: {:?}",
 363                     adt_def,
 364                     cv.ty()
 365                 );
 366                 let path = tcx.def_path_str(adt_def.did());
 367                 let msg = format!(
 368                     "to use a constant of type `{}` in a pattern, \
 369                      `{}` must be annotated with `#[derive(PartialEq, Eq)]`",
 370                     path, path,
 371                 );
 372                 self.saw_const_match_error.set(true);
 373                 if self.include_lint_checks {
 374                     tcx.sess.span_err(span, &msg);
 375                 } else {
 376                     tcx.sess.delay_span_bug(span, &msg);
 377                 }
 378                 PatKind::Wild
 379             }
 380             ty::Adt(adt_def, substs) if adt_def.is_enum() => {
 381                 let destructured = tcx.destructure_mir_constant(param_env, cv);
 382
 383                 PatKind::Variant {
 384                     adt_def: *adt_def,
 385                     substs,
 386                     variant_index: destructured
 387                         .variant
 388                         .expect("destructed const of adt without variant id"),
 389                     subpatterns: self.field_pats(destructured.fields.iter().copied())?,
 390                 }
 391             }
 392             ty::Tuple(_) | ty::Adt(_, _) => {
 393                 let destructured = tcx.destructure_mir_constant(param_env, cv);
 394                 PatKind::Leaf { subpatterns: self.field_pats(destructured.fields.iter().copied())? }
 395             }
 396             ty::Array(..) => PatKind::Array {
 397                 prefix: tcx
 398                     .destructure_mir_constant(param_env, cv)
 399                     .fields
 400                     .iter()
 401                     .map(|val| self.recur(*val, false))
 402                     .collect::<Result<_, _>>()?,
 403                 slice: None,
 404                 suffix: Vec::new(),
 405             },
 406             ty::Ref(_, pointee_ty, ..) => match *pointee_ty.kind() {
 407                 // These are not allowed and will error elsewhere anyway.
 408                 ty::Dynamic(..) => {
 409                     self.saw_const_match_error.set(true);
 410                     let msg = format!("`{}` cannot be used in patterns", cv.ty());
 411                     if self.include_lint_checks {
 412                         tcx.sess.span_err(span, &msg);
 413                     } else {
 414                         tcx.sess.delay_span_bug(span, &msg);
 415                     }
 416                     PatKind::Wild
 417                 }
 418                 // `&str` is represented as `ConstValue::Slice`, let's keep using this
 419                 // optimization for now.
 420                 ty::Str => PatKind::Constant { value: cv },
 421                 // `b"foo"` produces a `&[u8; 3]`, but you can't use constants of array type when
 422                 // matching against references, you can only use byte string literals.
 423                 // The typechecker has a special case for byte string literals, by treating them
 424                 // as slices. This means we turn `&[T; N]` constants into slice patterns, which
 425                 // has no negative effects on pattern matching, even if we're actually matching on
 426                 // arrays.
 427                 ty::Array(..) if !self.treat_byte_string_as_slice => {
 428                     let old = self.behind_reference.replace(true);
 429                     let array = tcx.deref_mir_constant(self.param_env.and(cv));
 430                     let val = PatKind::Deref {
 431                         subpattern: Pat {
 432                             kind: Box::new(PatKind::Array {
 433                                 prefix: tcx
 434                                     .destructure_mir_constant(param_env, array)
 435                                     .fields
 436                                     .iter()
 437                                     .map(|val| self.recur(*val, false))
 438                                     .collect::<Result<_, _>>()?,
 439                                 slice: None,
 440                                 suffix: vec![],
 441                             }),
 442                             span,
 443                             ty: *pointee_ty,
 444                         },
 445                     };
 446                     self.behind_reference.set(old);
 447                     val
 448                 }
 449                 ty::Array(elem_ty, _) |
 450                 // Cannot merge this with the catch all branch below, because the `const_deref`
 451                 // changes the type from slice to array, we need to keep the original type in the
 452                 // pattern.
 453                 ty::Slice(elem_ty) => {
 454                     let old = self.behind_reference.replace(true);
 455                     let array = tcx.deref_mir_constant(self.param_env.and(cv));
 456                     let val = PatKind::Deref {
 457                         subpattern: Pat {
 458                             kind: Box::new(PatKind::Slice {
 459                                 prefix: tcx
 460                                     .destructure_mir_constant(param_env, array)
 461                                     .fields
 462                                     .iter()
 463                                     .map(|val| self.recur(*val, false))
 464                                     .collect::<Result<_, _>>()?,
 465                                 slice: None,
 466                                 suffix: vec![],
 467                             }),
 468                             span,
 469                             ty: tcx.mk_slice(elem_ty),
 470                         },
 471                     };
 472                     self.behind_reference.set(old);
 473                     val
 474                 }
 475                 // Backwards compatibility hack: support references to non-structural types.
 476                 // We'll lower
 477                 // this pattern to a `PartialEq::eq` comparison and `PartialEq::eq` takes a
 478                 // reference. This makes the rest of the matching logic simpler as it doesn't have
 479                 // to figure out how to get a reference again.
 480                 ty::Adt(adt_def, _) if !self.type_marked_structural(*pointee_ty) => {
 481                     if self.behind_reference.get() {
 482                         if self.include_lint_checks
 483                             && !self.saw_const_match_error.get()
 484                             && !self.saw_const_match_lint.get()
 485                         {
 486                             self.saw_const_match_lint.set(true);
 487                             let msg = self.adt_derive_msg(adt_def);
 488                             self.tcx().struct_span_lint_hir(
 489                                 lint::builtin::INDIRECT_STRUCTURAL_MATCH,
 490                                 self.id,
 491                                 self.span,
 492                                 |lint| {lint.build(&msg).emit();},
 493                             );
 494                         }
 495                         PatKind::Constant { value: cv }
 496                     } else {
 497                         if !self.saw_const_match_error.get() {
 498                             self.saw_const_match_error.set(true);
 499                             let msg = self.adt_derive_msg(adt_def);
 500                             if self.include_lint_checks {
 501                                 tcx.sess.span_err(span, &msg);
 502                             } else {
 503                                 tcx.sess.delay_span_bug(span, &msg);
 504                             }
 505                         }
 506                         PatKind::Wild
 507                     }
 508                 }
 509                 // All other references are converted into deref patterns and then recursively
 510                 // convert the dereferenced constant to a pattern that is the sub-pattern of the
 511                 // deref pattern.
 512                 _ => {
 513                     if !pointee_ty.is_sized(tcx.at(span), param_env) {
 514                         // `tcx.deref_mir_constant()` below will ICE with an unsized type
 515                         // (except slices, which are handled in a separate arm above).
 516                         let msg = format!("cannot use unsized non-slice type `{}` in constant patterns", pointee_ty);
 517                         if self.include_lint_checks {
 518                             tcx.sess.span_err(span, &msg);
 519                         } else {
 520                             tcx.sess.delay_span_bug(span, &msg);
 521                         }
 522                         PatKind::Wild
 523                     } else {
 524                         let old = self.behind_reference.replace(true);
 525                         // In case there are structural-match violations somewhere in this subpattern,
 526                         // we fall back to a const pattern. If we do not do this, we may end up with
 527                         // a !structural-match constant that is not of reference type, which makes it
 528                         // very hard to invoke `PartialEq::eq` on it as a fallback.
 529                         let val = match self.recur(tcx.deref_mir_constant(self.param_env.and(cv)), false) {
 530                             Ok(subpattern) => PatKind::Deref { subpattern },
 531                             Err(_) => PatKind::Constant { value: cv },
 532                         };
 533                         self.behind_reference.set(old);
 534                         val
 535                     }
 536                 }
 537             },
 538             ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) | ty::FnDef(..) => {
 539                 PatKind::Constant { value: cv }
 540             }
 541             ty::RawPtr(pointee) if pointee.ty.is_sized(tcx.at(span), param_env) => {
 542                 PatKind::Constant { value: cv }
 543             }
 544             // FIXME: these can have very surprising behaviour where optimization levels or other
 545             // compilation choices change the runtime behaviour of the match.
 546             // See https://github.com/rust-lang/rust/issues/70861 for examples.
 547             ty::FnPtr(..) | ty::RawPtr(..) => {
 548                 if self.include_lint_checks
 549                     && !self.saw_const_match_error.get()
 550                     && !self.saw_const_match_lint.get()
 551                 {
 552                     self.saw_const_match_lint.set(true);
 553                     let msg = "function pointers and unsized pointers in patterns behave \
 554                         unpredictably and should not be relied upon. \
 555                         See https://github.com/rust-lang/rust/issues/70861 for details.";
 556                     tcx.struct_span_lint_hir(
 557                         lint::builtin::POINTER_STRUCTURAL_MATCH,
 558                         id,
 559                         span,
 560                         |lint| {
 561                             lint.build(msg).emit();
 562                         },
 563                     );
 564                 }
 565                 PatKind::Constant { value: cv }
 566             }
 567             _ => {
 568                 self.saw_const_match_error.set(true);
 569                 let msg = format!("`{}` cannot be used in patterns", cv.ty());
 570                 if self.include_lint_checks {
 571                     tcx.sess.span_err(span, &msg);
 572                 } else {
 573                     tcx.sess.delay_span_bug(span, &msg);
 574                 }
 575                 PatKind::Wild
 576             }
 577         };
 578
 579         if self.include_lint_checks
 580             && !self.saw_const_match_error.get()
 581             && !self.saw_const_match_lint.get()
 582             && mir_structural_match_violation
 583             // FIXME(#73448): Find a way to bring const qualification into parity with
 584             // `search_for_structural_match_violation` and then remove this condition.
 585             && self.search_for_structural_match_violation(cv.ty()).is_some()
 586         {
 587             self.saw_const_match_lint.set(true);
 588             // Obtain the actual type that isn't annotated. If we just looked at `cv.ty` we
 589             // could get `Option<NonStructEq>`, even though `Option` is annotated with derive.
 590             let msg = self.search_for_structural_match_violation(cv.ty()).unwrap().replace(
 591                 "in a pattern,",
 592                 "in a pattern, the constant's initializer must be trivial or",
 593             );
 594             tcx.struct_span_lint_hir(
 595                 lint::builtin::NONTRIVIAL_STRUCTURAL_MATCH,
 596                 id,
 597                 span,
 598                 |lint| {
 599                     lint.build(&msg).emit();
 600                 },
 601             );
 602         }
 603
 604         Ok(Pat { span, ty: cv.ty(), kind: Box::new(kind) })
 605     }
 606 }