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