compiler/rustc_const_eval/src/transform/check_consts/check.rs

   1 //! The `Visitor` responsible for actually checking a `mir::Body` for invalid operations.
   2
   3 use rustc_errors::{Applicability, Diagnostic, ErrorReported};
   4 use rustc_hir::def_id::DefId;
   5 use rustc_hir::{self as hir, HirId, LangItem};
   6 use rustc_index::bit_set::BitSet;
   7 use rustc_infer::infer::TyCtxtInferExt;
   8 use rustc_infer::traits::{ImplSource, Obligation, ObligationCause};
   9 use rustc_middle::mir::visit::{MutatingUseContext, NonMutatingUseContext, PlaceContext, Visitor};
  10 use rustc_middle::mir::*;
  11 use rustc_middle::ty::cast::CastTy;
  12 use rustc_middle::ty::subst::{GenericArgKind, InternalSubsts};
  13 use rustc_middle::ty::{self, adjustment::PointerCast, Instance, InstanceDef, Ty, TyCtxt};
  14 use rustc_middle::ty::{Binder, TraitPredicate, TraitRef};
  15 use rustc_mir_dataflow::{self, Analysis};
  16 use rustc_span::{sym, Span, Symbol};
  17 use rustc_trait_selection::traits::error_reporting::InferCtxtExt;
  18 use rustc_trait_selection::traits::{self, SelectionContext, TraitEngine};
  19
  20 use std::mem;
  21 use std::ops::Deref;
  22
  23 use super::ops::{self, NonConstOp, Status};
  24 use super::qualifs::{self, CustomEq, HasMutInterior, NeedsDrop, NeedsNonConstDrop};
  25 use super::resolver::FlowSensitiveAnalysis;
  26 use super::{ConstCx, Qualif};
  27 use crate::const_eval::is_unstable_const_fn;
  28
  29 type QualifResults<'mir, 'tcx, Q> =
  30     rustc_mir_dataflow::ResultsCursor<'mir, 'tcx, FlowSensitiveAnalysis<'mir, 'mir, 'tcx, Q>>;
  31
  32 #[derive(Default)]
  33 pub struct Qualifs<'mir, 'tcx> {
  34     has_mut_interior: Option<QualifResults<'mir, 'tcx, HasMutInterior>>,
  35     needs_drop: Option<QualifResults<'mir, 'tcx, NeedsDrop>>,
  36     needs_non_const_drop: Option<QualifResults<'mir, 'tcx, NeedsNonConstDrop>>,
  37 }
  38
  39 impl Qualifs<'mir, 'tcx> {
  40     /// Returns `true` if `local` is `NeedsDrop` at the given `Location`.
  41     ///
  42     /// Only updates the cursor if absolutely necessary
  43     pub fn needs_drop(
  44         &mut self,
  45         ccx: &'mir ConstCx<'mir, 'tcx>,
  46         local: Local,
  47         location: Location,
  48     ) -> bool {
  49         let ty = ccx.body.local_decls[local].ty;
  50         if !NeedsDrop::in_any_value_of_ty(ccx, ty) {
  51             return false;
  52         }
  53
  54         let needs_drop = self.needs_drop.get_or_insert_with(|| {
  55             let ConstCx { tcx, body, .. } = *ccx;
  56
  57             FlowSensitiveAnalysis::new(NeedsDrop, ccx)
  58                 .into_engine(tcx, &body)
  59                 .iterate_to_fixpoint()
  60                 .into_results_cursor(&body)
  61         });
  62
  63         needs_drop.seek_before_primary_effect(location);
  64         needs_drop.get().contains(local)
  65     }
  66
  67     /// Returns `true` if `local` is `NeedsNonConstDrop` at the given `Location`.
  68     ///
  69     /// Only updates the cursor if absolutely necessary
  70     pub fn needs_non_const_drop(
  71         &mut self,
  72         ccx: &'mir ConstCx<'mir, 'tcx>,
  73         local: Local,
  74         location: Location,
  75     ) -> bool {
  76         let ty = ccx.body.local_decls[local].ty;
  77         if !NeedsNonConstDrop::in_any_value_of_ty(ccx, ty) {
  78             return false;
  79         }
  80
  81         let needs_non_const_drop = self.needs_non_const_drop.get_or_insert_with(|| {
  82             let ConstCx { tcx, body, .. } = *ccx;
  83
  84             FlowSensitiveAnalysis::new(NeedsNonConstDrop, ccx)
  85                 .into_engine(tcx, &body)
  86                 .iterate_to_fixpoint()
  87                 .into_results_cursor(&body)
  88         });
  89
  90         needs_non_const_drop.seek_before_primary_effect(location);
  91         needs_non_const_drop.get().contains(local)
  92     }
  93
  94     /// Returns `true` if `local` is `HasMutInterior` at the given `Location`.
  95     ///
  96     /// Only updates the cursor if absolutely necessary.
  97     pub fn has_mut_interior(
  98         &mut self,
  99         ccx: &'mir ConstCx<'mir, 'tcx>,
 100         local: Local,
 101         location: Location,
 102     ) -> bool {
 103         let ty = ccx.body.local_decls[local].ty;
 104         if !HasMutInterior::in_any_value_of_ty(ccx, ty) {
 105             return false;
 106         }
 107
 108         let has_mut_interior = self.has_mut_interior.get_or_insert_with(|| {
 109             let ConstCx { tcx, body, .. } = *ccx;
 110
 111             FlowSensitiveAnalysis::new(HasMutInterior, ccx)
 112                 .into_engine(tcx, &body)
 113                 .iterate_to_fixpoint()
 114                 .into_results_cursor(&body)
 115         });
 116
 117         has_mut_interior.seek_before_primary_effect(location);
 118         has_mut_interior.get().contains(local)
 119     }
 120
 121     fn in_return_place(
 122         &mut self,
 123         ccx: &'mir ConstCx<'mir, 'tcx>,
 124         error_occured: Option<ErrorReported>,
 125     ) -> ConstQualifs {
 126         // Find the `Return` terminator if one exists.
 127         //
 128         // If no `Return` terminator exists, this MIR is divergent. Just return the conservative
 129         // qualifs for the return type.
 130         let return_block = ccx
 131             .body
 132             .basic_blocks()
 133             .iter_enumerated()
 134             .find(|(_, block)| matches!(block.terminator().kind, TerminatorKind::Return))
 135             .map(|(bb, _)| bb);
 136
 137         let return_block = match return_block {
 138             None => return qualifs::in_any_value_of_ty(ccx, ccx.body.return_ty(), error_occured),
 139             Some(bb) => bb,
 140         };
 141
 142         let return_loc = ccx.body.terminator_loc(return_block);
 143
 144         let custom_eq = match ccx.const_kind() {
 145             // We don't care whether a `const fn` returns a value that is not structurally
 146             // matchable. Functions calls are opaque and always use type-based qualification, so
 147             // this value should never be used.
 148             hir::ConstContext::ConstFn => true,
 149
 150             // If we know that all values of the return type are structurally matchable, there's no
 151             // need to run dataflow.
 152             _ if !CustomEq::in_any_value_of_ty(ccx, ccx.body.return_ty()) => false,
 153
 154             hir::ConstContext::Const | hir::ConstContext::Static(_) => {
 155                 let mut cursor = FlowSensitiveAnalysis::new(CustomEq, ccx)
 156                     .into_engine(ccx.tcx, &ccx.body)
 157                     .iterate_to_fixpoint()
 158                     .into_results_cursor(&ccx.body);
 159
 160                 cursor.seek_after_primary_effect(return_loc);
 161                 cursor.get().contains(RETURN_PLACE)
 162             }
 163         };
 164
 165         ConstQualifs {
 166             needs_drop: self.needs_drop(ccx, RETURN_PLACE, return_loc),
 167             needs_non_const_drop: self.needs_non_const_drop(ccx, RETURN_PLACE, return_loc),
 168             has_mut_interior: self.has_mut_interior(ccx, RETURN_PLACE, return_loc),
 169             custom_eq,
 170             error_occured,
 171         }
 172     }
 173 }
 174
 175 pub struct Checker<'mir, 'tcx> {
 176     ccx: &'mir ConstCx<'mir, 'tcx>,
 177     qualifs: Qualifs<'mir, 'tcx>,
 178
 179     /// The span of the current statement.
 180     span: Span,
 181
 182     /// A set that stores for each local whether it has a `StorageDead` for it somewhere.
 183     local_has_storage_dead: Option<BitSet<Local>>,
 184
 185     error_emitted: Option<ErrorReported>,
 186     secondary_errors: Vec<Diagnostic>,
 187 }
 188
 189 impl Deref for Checker<'mir, 'tcx> {
 190     type Target = ConstCx<'mir, 'tcx>;
 191
 192     fn deref(&self) -> &Self::Target {
 193         &self.ccx
 194     }
 195 }
 196
 197 impl Checker<'mir, 'tcx> {
 198     pub fn new(ccx: &'mir ConstCx<'mir, 'tcx>) -> Self {
 199         Checker {
 200             span: ccx.body.span,
 201             ccx,
 202             qualifs: Default::default(),
 203             local_has_storage_dead: None,
 204             error_emitted: None,
 205             secondary_errors: Vec::new(),
 206         }
 207     }
 208
 209     pub fn check_body(&mut self) {
 210         let ConstCx { tcx, body, .. } = *self.ccx;
 211         let def_id = self.ccx.def_id();
 212
 213         // `async` functions cannot be `const fn`. This is checked during AST lowering, so there's
 214         // no need to emit duplicate errors here.
 215         if is_async_fn(self.ccx) || body.generator.is_some() {
 216             tcx.sess.delay_span_bug(body.span, "`async` functions cannot be `const fn`");
 217             return;
 218         }
 219
 220         // The local type and predicate checks are not free and only relevant for `const fn`s.
 221         if self.const_kind() == hir::ConstContext::ConstFn {
 222             // Prevent const trait methods from being annotated as `stable`.
 223             // FIXME: Do this as part of stability checking.
 224             if self.is_const_stable_const_fn() {
 225                 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
 226                 if crate::const_eval::is_parent_const_impl_raw(tcx, hir_id) {
 227                     self.ccx
 228                         .tcx
 229                         .sess
 230                         .struct_span_err(self.span, "trait methods cannot be stable const fn")
 231                         .emit();
 232                 }
 233             }
 234
 235             self.check_item_predicates();
 236
 237             for (idx, local) in body.local_decls.iter_enumerated() {
 238                 // Handle the return place below.
 239                 if idx == RETURN_PLACE || local.internal {
 240                     continue;
 241                 }
 242
 243                 self.span = local.source_info.span;
 244                 self.check_local_or_return_ty(local.ty, idx);
 245             }
 246
 247             // impl trait is gone in MIR, so check the return type of a const fn by its signature
 248             // instead of the type of the return place.
 249             self.span = body.local_decls[RETURN_PLACE].source_info.span;
 250             let return_ty = tcx.fn_sig(def_id).output();
 251             self.check_local_or_return_ty(return_ty.skip_binder(), RETURN_PLACE);
 252         }
 253
 254         if !tcx.has_attr(def_id.to_def_id(), sym::rustc_do_not_const_check) {
 255             self.visit_body(&body);
 256         }
 257
 258         // Ensure that the end result is `Sync` in a non-thread local `static`.
 259         let should_check_for_sync = self.const_kind()
 260             == hir::ConstContext::Static(hir::Mutability::Not)
 261             && !tcx.is_thread_local_static(def_id.to_def_id());
 262
 263         if should_check_for_sync {
 264             let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
 265             check_return_ty_is_sync(tcx, &body, hir_id);
 266         }
 267
 268         // If we got through const-checking without emitting any "primary" errors, emit any
 269         // "secondary" errors if they occurred.
 270         let secondary_errors = mem::take(&mut self.secondary_errors);
 271         if self.error_emitted.is_none() {
 272             for error in secondary_errors {
 273                 self.tcx.sess.diagnostic().emit_diagnostic(&error);
 274             }
 275         } else {
 276             assert!(self.tcx.sess.has_errors());
 277         }
 278     }
 279
 280     fn local_has_storage_dead(&mut self, local: Local) -> bool {
 281         let ccx = self.ccx;
 282         self.local_has_storage_dead
 283             .get_or_insert_with(|| {
 284                 struct StorageDeads {
 285                     locals: BitSet<Local>,
 286                 }
 287                 impl Visitor<'tcx> for StorageDeads {
 288                     fn visit_statement(&mut self, stmt: &Statement<'tcx>, _: Location) {
 289                         if let StatementKind::StorageDead(l) = stmt.kind {
 290                             self.locals.insert(l);
 291                         }
 292                     }
 293                 }
 294                 let mut v = StorageDeads { locals: BitSet::new_empty(ccx.body.local_decls.len()) };
 295                 v.visit_body(ccx.body);
 296                 v.locals
 297             })
 298             .contains(local)
 299     }
 300
 301     pub fn qualifs_in_return_place(&mut self) -> ConstQualifs {
 302         self.qualifs.in_return_place(self.ccx, self.error_emitted)
 303     }
 304
 305     /// Emits an error if an expression cannot be evaluated in the current context.
 306     pub fn check_op(&mut self, op: impl NonConstOp) {
 307         self.check_op_spanned(op, self.span);
 308     }
 309
 310     /// Emits an error at the given `span` if an expression cannot be evaluated in the current
 311     /// context.
 312     pub fn check_op_spanned<O: NonConstOp>(&mut self, op: O, span: Span) {
 313         let gate = match op.status_in_item(self.ccx) {
 314             Status::Allowed => return,
 315
 316             Status::Unstable(gate) if self.tcx.features().enabled(gate) => {
 317                 let unstable_in_stable = self.ccx.is_const_stable_const_fn()
 318                     && !super::rustc_allow_const_fn_unstable(
 319                         self.tcx,
 320                         self.def_id().to_def_id(),
 321                         gate,
 322                     );
 323                 if unstable_in_stable {
 324                     emit_unstable_in_stable_error(self.ccx, span, gate);
 325                 }
 326
 327                 return;
 328             }
 329
 330             Status::Unstable(gate) => Some(gate),
 331             Status::Forbidden => None,
 332         };
 333
 334         if self.tcx.sess.opts.debugging_opts.unleash_the_miri_inside_of_you {
 335             self.tcx.sess.miri_unleashed_feature(span, gate);
 336             return;
 337         }
 338
 339         let mut err = op.build_error(self.ccx, span);
 340         assert!(err.is_error());
 341
 342         match op.importance() {
 343             ops::DiagnosticImportance::Primary => {
 344                 self.error_emitted = Some(ErrorReported);
 345                 err.emit();
 346             }
 347
 348             ops::DiagnosticImportance::Secondary => err.buffer(&mut self.secondary_errors),
 349         }
 350     }
 351
 352     fn check_static(&mut self, def_id: DefId, span: Span) {
 353         if self.tcx.is_thread_local_static(def_id) {
 354             self.tcx.sess.delay_span_bug(span, "tls access is checked in `Rvalue::ThreadLocalRef");
 355         }
 356         self.check_op_spanned(ops::StaticAccess, span)
 357     }
 358
 359     fn check_local_or_return_ty(&mut self, ty: Ty<'tcx>, local: Local) {
 360         let kind = self.body.local_kind(local);
 361
 362         for ty in ty.walk(self.tcx) {
 363             let ty = match ty.unpack() {
 364                 GenericArgKind::Type(ty) => ty,
 365
 366                 // No constraints on lifetimes or constants, except potentially
 367                 // constants' types, but `walk` will get to them as well.
 368                 GenericArgKind::Lifetime(_) | GenericArgKind::Const(_) => continue,
 369             };
 370
 371             match *ty.kind() {
 372                 ty::Ref(_, _, hir::Mutability::Mut) => self.check_op(ops::ty::MutRef(kind)),
 373                 ty::Opaque(..) => self.check_op(ops::ty::ImplTrait),
 374                 ty::FnPtr(..) => self.check_op(ops::ty::FnPtr(kind)),
 375
 376                 ty::Dynamic(preds, _) => {
 377                     for pred in preds.iter() {
 378                         match pred.skip_binder() {
 379                             ty::ExistentialPredicate::AutoTrait(_)
 380                             | ty::ExistentialPredicate::Projection(_) => {
 381                                 self.check_op(ops::ty::DynTrait(kind))
 382                             }
 383                             ty::ExistentialPredicate::Trait(trait_ref) => {
 384                                 if Some(trait_ref.def_id) != self.tcx.lang_items().sized_trait() {
 385                                     self.check_op(ops::ty::DynTrait(kind))
 386                                 }
 387                             }
 388                         }
 389                     }
 390                 }
 391                 _ => {}
 392             }
 393         }
 394     }
 395
 396     fn check_item_predicates(&mut self) {
 397         let ConstCx { tcx, .. } = *self.ccx;
 398
 399         let mut current = self.def_id().to_def_id();
 400         loop {
 401             let predicates = tcx.predicates_of(current);
 402             for (predicate, _) in predicates.predicates {
 403                 match predicate.kind().skip_binder() {
 404                     ty::PredicateKind::RegionOutlives(_)
 405                     | ty::PredicateKind::TypeOutlives(_)
 406                     | ty::PredicateKind::WellFormed(_)
 407                     | ty::PredicateKind::Projection(_)
 408                     | ty::PredicateKind::ConstEvaluatable(..)
 409                     | ty::PredicateKind::ConstEquate(..)
 410                     | ty::PredicateKind::TypeWellFormedFromEnv(..) => continue,
 411                     ty::PredicateKind::ObjectSafe(_) => {
 412                         bug!("object safe predicate on function: {:#?}", predicate)
 413                     }
 414                     ty::PredicateKind::ClosureKind(..) => {
 415                         bug!("closure kind predicate on function: {:#?}", predicate)
 416                     }
 417                     ty::PredicateKind::Subtype(_) | ty::PredicateKind::Coerce(_) => {
 418                         bug!("subtype/coerce predicate on function: {:#?}", predicate)
 419                     }
 420                     ty::PredicateKind::Trait(pred) => {
 421                         if Some(pred.def_id()) == tcx.lang_items().sized_trait() {
 422                             continue;
 423                         }
 424                         match pred.self_ty().kind() {
 425                             ty::Param(p) => {
 426                                 let generics = tcx.generics_of(current);
 427                                 let def = generics.type_param(p, tcx);
 428                                 let span = tcx.def_span(def.def_id);
 429
 430                                 // These are part of the function signature, so treat them like
 431                                 // arguments when determining importance.
 432                                 let kind = LocalKind::Arg;
 433
 434                                 self.check_op_spanned(ops::ty::TraitBound(kind), span);
 435                             }
 436                             // other kinds of bounds are either tautologies
 437                             // or cause errors in other passes
 438                             _ => continue,
 439                         }
 440                     }
 441                 }
 442             }
 443             match predicates.parent {
 444                 Some(parent) => current = parent,
 445                 None => break,
 446             }
 447         }
 448     }
 449
 450     fn check_mut_borrow(&mut self, local: Local, kind: hir::BorrowKind) {
 451         match self.const_kind() {
 452             // In a const fn all borrows are transient or point to the places given via
 453             // references in the arguments (so we already checked them with
 454             // TransientMutBorrow/MutBorrow as appropriate).
 455             // The borrow checker guarantees that no new non-transient borrows are created.
 456             // NOTE: Once we have heap allocations during CTFE we need to figure out
 457             // how to prevent `const fn` to create long-lived allocations that point
 458             // to mutable memory.
 459             hir::ConstContext::ConstFn => self.check_op(ops::TransientMutBorrow(kind)),
 460             _ => {
 461                 // Locals with StorageDead do not live beyond the evaluation and can
 462                 // thus safely be borrowed without being able to be leaked to the final
 463                 // value of the constant.
 464                 if self.local_has_storage_dead(local) {
 465                     self.check_op(ops::TransientMutBorrow(kind));
 466                 } else {
 467                     self.check_op(ops::MutBorrow(kind));
 468                 }
 469             }
 470         }
 471     }
 472 }
 473
 474 impl Visitor<'tcx> for Checker<'mir, 'tcx> {
 475     fn visit_basic_block_data(&mut self, bb: BasicBlock, block: &BasicBlockData<'tcx>) {
 476         trace!("visit_basic_block_data: bb={:?} is_cleanup={:?}", bb, block.is_cleanup);
 477
 478         // We don't const-check basic blocks on the cleanup path since we never unwind during
 479         // const-eval: a panic causes an immediate compile error. In other words, cleanup blocks
 480         // are unreachable during const-eval.
 481         //
 482         // We can't be more conservative (e.g., by const-checking cleanup blocks anyways) because
 483         // locals that would never be dropped during normal execution are sometimes dropped during
 484         // unwinding, which means backwards-incompatible live-drop errors.
 485         if block.is_cleanup {
 486             return;
 487         }
 488
 489         self.super_basic_block_data(bb, block);
 490     }
 491
 492     fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, location: Location) {
 493         trace!("visit_rvalue: rvalue={:?} location={:?}", rvalue, location);
 494
 495         // Special-case reborrows to be more like a copy of a reference.
 496         match *rvalue {
 497             Rvalue::Ref(_, kind, place) => {
 498                 if let Some(reborrowed_place_ref) = place_as_reborrow(self.tcx, self.body, place) {
 499                     let ctx = match kind {
 500                         BorrowKind::Shared => {
 501                             PlaceContext::NonMutatingUse(NonMutatingUseContext::SharedBorrow)
 502                         }
 503                         BorrowKind::Shallow => {
 504                             PlaceContext::NonMutatingUse(NonMutatingUseContext::ShallowBorrow)
 505                         }
 506                         BorrowKind::Unique => {
 507                             PlaceContext::NonMutatingUse(NonMutatingUseContext::UniqueBorrow)
 508                         }
 509                         BorrowKind::Mut { .. } => {
 510                             PlaceContext::MutatingUse(MutatingUseContext::Borrow)
 511                         }
 512                     };
 513                     self.visit_local(&reborrowed_place_ref.local, ctx, location);
 514                     self.visit_projection(reborrowed_place_ref, ctx, location);
 515                     return;
 516                 }
 517             }
 518             Rvalue::AddressOf(mutbl, place) => {
 519                 if let Some(reborrowed_place_ref) = place_as_reborrow(self.tcx, self.body, place) {
 520                     let ctx = match mutbl {
 521                         Mutability::Not => {
 522                             PlaceContext::NonMutatingUse(NonMutatingUseContext::AddressOf)
 523                         }
 524                         Mutability::Mut => PlaceContext::MutatingUse(MutatingUseContext::AddressOf),
 525                     };
 526                     self.visit_local(&reborrowed_place_ref.local, ctx, location);
 527                     self.visit_projection(reborrowed_place_ref, ctx, location);
 528                     return;
 529                 }
 530             }
 531             _ => {}
 532         }
 533
 534         self.super_rvalue(rvalue, location);
 535
 536         match *rvalue {
 537             Rvalue::ThreadLocalRef(_) => self.check_op(ops::ThreadLocalAccess),
 538
 539             Rvalue::Use(_)
 540             | Rvalue::Repeat(..)
 541             | Rvalue::Discriminant(..)
 542             | Rvalue::Len(_)
 543             | Rvalue::Aggregate(..) => {}
 544
 545             Rvalue::Ref(_, kind @ BorrowKind::Mut { .. }, ref place)
 546             | Rvalue::Ref(_, kind @ BorrowKind::Unique, ref place) => {
 547                 let ty = place.ty(self.body, self.tcx).ty;
 548                 let is_allowed = match ty.kind() {
 549                     // Inside a `static mut`, `&mut [...]` is allowed.
 550                     ty::Array(..) | ty::Slice(_)
 551                         if self.const_kind() == hir::ConstContext::Static(hir::Mutability::Mut) =>
 552                     {
 553                         true
 554                     }
 555
 556                     // FIXME(ecstaticmorse): We could allow `&mut []` inside a const context given
 557                     // that this is merely a ZST and it is already eligible for promotion.
 558                     // This may require an RFC?
 559                     /*
 560                     ty::Array(_, len) if len.try_eval_usize(cx.tcx, cx.param_env) == Some(0)
 561                         => true,
 562                     */
 563                     _ => false,
 564                 };
 565
 566                 if !is_allowed {
 567                     if let BorrowKind::Mut { .. } = kind {
 568                         self.check_mut_borrow(place.local, hir::BorrowKind::Ref)
 569                     } else {
 570                         self.check_op(ops::CellBorrow);
 571                     }
 572                 }
 573             }
 574
 575             Rvalue::AddressOf(Mutability::Mut, ref place) => {
 576                 self.check_mut_borrow(place.local, hir::BorrowKind::Raw)
 577             }
 578
 579             Rvalue::Ref(_, BorrowKind::Shared | BorrowKind::Shallow, ref place)
 580             | Rvalue::AddressOf(Mutability::Not, ref place) => {
 581                 let borrowed_place_has_mut_interior = qualifs::in_place::<HasMutInterior, _>(
 582                     &self.ccx,
 583                     &mut |local| self.qualifs.has_mut_interior(self.ccx, local, location),
 584                     place.as_ref(),
 585                 );
 586
 587                 if borrowed_place_has_mut_interior {
 588                     match self.const_kind() {
 589                         // In a const fn all borrows are transient or point to the places given via
 590                         // references in the arguments (so we already checked them with
 591                         // TransientCellBorrow/CellBorrow as appropriate).
 592                         // The borrow checker guarantees that no new non-transient borrows are created.
 593                         // NOTE: Once we have heap allocations during CTFE we need to figure out
 594                         // how to prevent `const fn` to create long-lived allocations that point
 595                         // to (interior) mutable memory.
 596                         hir::ConstContext::ConstFn => self.check_op(ops::TransientCellBorrow),
 597                         _ => {
 598                             // Locals with StorageDead are definitely not part of the final constant value, and
 599                             // it is thus inherently safe to permit such locals to have their
 600                             // address taken as we can't end up with a reference to them in the
 601                             // final value.
 602                             // Note: This is only sound if every local that has a `StorageDead` has a
 603                             // `StorageDead` in every control flow path leading to a `return` terminator.
 604                             if self.local_has_storage_dead(place.local) {
 605                                 self.check_op(ops::TransientCellBorrow);
 606                             } else {
 607                                 self.check_op(ops::CellBorrow);
 608                             }
 609                         }
 610                     }
 611                 }
 612             }
 613
 614             Rvalue::Cast(
 615                 CastKind::Pointer(PointerCast::MutToConstPointer | PointerCast::ArrayToPointer),
 616                 _,
 617                 _,
 618             ) => {}
 619
 620             Rvalue::Cast(
 621                 CastKind::Pointer(
 622                     PointerCast::UnsafeFnPointer
 623                     | PointerCast::ClosureFnPointer(_)
 624                     | PointerCast::ReifyFnPointer,
 625                 ),
 626                 _,
 627                 _,
 628             ) => self.check_op(ops::FnPtrCast),
 629
 630             Rvalue::Cast(CastKind::Pointer(PointerCast::Unsize), _, _) => {
 631                 // Nothing to check here (`check_local_or_return_ty` ensures no trait objects occur
 632                 // in the type of any local, which also excludes casts).
 633             }
 634
 635             Rvalue::Cast(CastKind::Misc, ref operand, cast_ty) => {
 636                 let operand_ty = operand.ty(self.body, self.tcx);
 637                 let cast_in = CastTy::from_ty(operand_ty).expect("bad input type for cast");
 638                 let cast_out = CastTy::from_ty(cast_ty).expect("bad output type for cast");
 639
 640                 if let (CastTy::Ptr(_) | CastTy::FnPtr, CastTy::Int(_)) = (cast_in, cast_out) {
 641                     self.check_op(ops::RawPtrToIntCast);
 642                 }
 643             }
 644
 645             Rvalue::NullaryOp(NullOp::SizeOf | NullOp::AlignOf, _) => {}
 646             Rvalue::NullaryOp(NullOp::Box, _) => self.check_op(ops::HeapAllocation),
 647             Rvalue::ShallowInitBox(_, _) => {}
 648
 649             Rvalue::UnaryOp(_, ref operand) => {
 650                 let ty = operand.ty(self.body, self.tcx);
 651                 if is_int_bool_or_char(ty) {
 652                     // Int, bool, and char operations are fine.
 653                 } else if ty.is_floating_point() {
 654                     self.check_op(ops::FloatingPointOp);
 655                 } else {
 656                     span_bug!(self.span, "non-primitive type in `Rvalue::UnaryOp`: {:?}", ty);
 657                 }
 658             }
 659
 660             Rvalue::BinaryOp(op, box (ref lhs, ref rhs))
 661             | Rvalue::CheckedBinaryOp(op, box (ref lhs, ref rhs)) => {
 662                 let lhs_ty = lhs.ty(self.body, self.tcx);
 663                 let rhs_ty = rhs.ty(self.body, self.tcx);
 664
 665                 if is_int_bool_or_char(lhs_ty) && is_int_bool_or_char(rhs_ty) {
 666                     // Int, bool, and char operations are fine.
 667                 } else if lhs_ty.is_fn_ptr() || lhs_ty.is_unsafe_ptr() {
 668                     assert_eq!(lhs_ty, rhs_ty);
 669                     assert!(
 670                         op == BinOp::Eq
 671                             || op == BinOp::Ne
 672                             || op == BinOp::Le
 673                             || op == BinOp::Lt
 674                             || op == BinOp::Ge
 675                             || op == BinOp::Gt
 676                             || op == BinOp::Offset
 677                     );
 678
 679                     self.check_op(ops::RawPtrComparison);
 680                 } else if lhs_ty.is_floating_point() || rhs_ty.is_floating_point() {
 681                     self.check_op(ops::FloatingPointOp);
 682                 } else {
 683                     span_bug!(
 684                         self.span,
 685                         "non-primitive type in `Rvalue::BinaryOp`: {:?} ⚬ {:?}",
 686                         lhs_ty,
 687                         rhs_ty
 688                     );
 689                 }
 690             }
 691         }
 692     }
 693
 694     fn visit_operand(&mut self, op: &Operand<'tcx>, location: Location) {
 695         self.super_operand(op, location);
 696         if let Operand::Constant(c) = op {
 697             if let Some(def_id) = c.check_static_ptr(self.tcx) {
 698                 self.check_static(def_id, self.span);
 699             }
 700         }
 701     }
 702     fn visit_projection_elem(
 703         &mut self,
 704         place_local: Local,
 705         proj_base: &[PlaceElem<'tcx>],
 706         elem: PlaceElem<'tcx>,
 707         context: PlaceContext,
 708         location: Location,
 709     ) {
 710         trace!(
 711             "visit_projection_elem: place_local={:?} proj_base={:?} elem={:?} \
 712             context={:?} location={:?}",
 713             place_local,
 714             proj_base,
 715             elem,
 716             context,
 717             location,
 718         );
 719
 720         self.super_projection_elem(place_local, proj_base, elem, context, location);
 721
 722         match elem {
 723             ProjectionElem::Deref => {
 724                 let base_ty = Place::ty_from(place_local, proj_base, self.body, self.tcx).ty;
 725                 if let ty::RawPtr(_) = base_ty.kind() {
 726                     if proj_base.is_empty() {
 727                         let decl = &self.body.local_decls[place_local];
 728                         if let Some(box LocalInfo::StaticRef { def_id, .. }) = decl.local_info {
 729                             let span = decl.source_info.span;
 730                             self.check_static(def_id, span);
 731                             return;
 732                         }
 733                     }
 734                     self.check_op(ops::RawPtrDeref);
 735                 }
 736
 737                 if context.is_mutating_use() {
 738                     self.check_op(ops::MutDeref);
 739                 }
 740             }
 741
 742             ProjectionElem::ConstantIndex { .. }
 743             | ProjectionElem::Downcast(..)
 744             | ProjectionElem::Subslice { .. }
 745             | ProjectionElem::Field(..)
 746             | ProjectionElem::Index(_) => {}
 747         }
 748     }
 749
 750     fn visit_source_info(&mut self, source_info: &SourceInfo) {
 751         trace!("visit_source_info: source_info={:?}", source_info);
 752         self.span = source_info.span;
 753     }
 754
 755     fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) {
 756         trace!("visit_statement: statement={:?} location={:?}", statement, location);
 757
 758         self.super_statement(statement, location);
 759
 760         match statement.kind {
 761             StatementKind::LlvmInlineAsm { .. } => {
 762                 self.check_op(ops::InlineAsm);
 763             }
 764
 765             StatementKind::Assign(..)
 766             | StatementKind::SetDiscriminant { .. }
 767             | StatementKind::FakeRead(..)
 768             | StatementKind::StorageLive(_)
 769             | StatementKind::StorageDead(_)
 770             | StatementKind::Retag { .. }
 771             | StatementKind::AscribeUserType(..)
 772             | StatementKind::Coverage(..)
 773             | StatementKind::CopyNonOverlapping(..)
 774             | StatementKind::Nop => {}
 775         }
 776     }
 777
 778     #[instrument(level = "debug", skip(self))]
 779     fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location) {
 780         use rustc_target::spec::abi::Abi::RustIntrinsic;
 781
 782         self.super_terminator(terminator, location);
 783
 784         match &terminator.kind {
 785             TerminatorKind::Call { func, args, .. } => {
 786                 let ConstCx { tcx, body, param_env, .. } = *self.ccx;
 787                 let caller = self.def_id().to_def_id();
 788
 789                 let fn_ty = func.ty(body, tcx);
 790
 791                 let (mut callee, mut substs) = match *fn_ty.kind() {
 792                     ty::FnDef(def_id, substs) => (def_id, substs),
 793
 794                     ty::FnPtr(_) => {
 795                         self.check_op(ops::FnCallIndirect);
 796                         return;
 797                     }
 798                     _ => {
 799                         span_bug!(terminator.source_info.span, "invalid callee of type {:?}", fn_ty)
 800                     }
 801                 };
 802
 803                 let mut nonconst_call_permission = false;
 804
 805                 // Attempting to call a trait method?
 806                 if let Some(trait_id) = tcx.trait_of_item(callee) {
 807                     trace!("attempting to call a trait method");
 808                     if !self.tcx.features().const_trait_impl {
 809                         self.check_op(ops::FnCallNonConst);
 810                         return;
 811                     }
 812
 813                     let trait_ref = TraitRef::from_method(tcx, trait_id, substs);
 814                     let obligation = Obligation::new(
 815                         ObligationCause::dummy(),
 816                         param_env,
 817                         Binder::dummy(TraitPredicate {
 818                             trait_ref,
 819                             constness: ty::BoundConstness::ConstIfConst,
 820                             polarity: ty::ImplPolarity::Positive,
 821                         }),
 822                     );
 823
 824                     let implsrc = tcx.infer_ctxt().enter(|infcx| {
 825                         let mut selcx =
 826                             SelectionContext::with_constness(&infcx, hir::Constness::Const);
 827                         selcx.select(&obligation)
 828                     });
 829
 830                     match implsrc {
 831                         Ok(Some(ImplSource::Param(_, ty::BoundConstness::ConstIfConst))) => {
 832                             debug!(
 833                                 "const_trait_impl: provided {:?} via where-clause in {:?}",
 834                                 trait_ref, param_env
 835                             );
 836                             return;
 837                         }
 838                         Ok(Some(ImplSource::UserDefined(data))) => {
 839                             let callee_name = tcx.item_name(callee);
 840                             if let Some(&did) = tcx
 841                                 .associated_item_def_ids(data.impl_def_id)
 842                                 .iter()
 843                                 .find(|did| tcx.item_name(**did) == callee_name)
 844                             {
 845                                 // using internal substs is ok here, since this is only
 846                                 // used for the `resolve` call below
 847                                 substs = InternalSubsts::identity_for_item(tcx, did);
 848                                 callee = did;
 849                             }
 850                         }
 851                         _ if !tcx.is_const_fn_raw(callee) => {
 852                             // At this point, it is only legal when the caller is marked with
 853                             // #[default_method_body_is_const], and the callee is in the same
 854                             // trait.
 855                             let callee_trait = tcx.trait_of_item(callee);
 856                             if callee_trait.is_some() {
 857                                 if tcx.has_attr(caller, sym::default_method_body_is_const) {
 858                                     if tcx.trait_of_item(caller) == callee_trait {
 859                                         nonconst_call_permission = true;
 860                                     }
 861                                 }
 862                             }
 863
 864                             if !nonconst_call_permission {
 865                                 self.check_op(ops::FnCallNonConst);
 866                                 return;
 867                             }
 868                         }
 869                         _ => {}
 870                     }
 871
 872                     // Resolve a trait method call to its concrete implementation, which may be in a
 873                     // `const` trait impl.
 874                     let instance = Instance::resolve(tcx, param_env, callee, substs);
 875                     debug!("Resolving ({:?}) -> {:?}", callee, instance);
 876                     if let Ok(Some(func)) = instance {
 877                         if let InstanceDef::Item(def) = func.def {
 878                             callee = def.did;
 879                         }
 880                     }
 881                 }
 882
 883                 // At this point, we are calling a function, `callee`, whose `DefId` is known...
 884
 885                 // `begin_panic` and `panic_display` are generic functions that accept
 886                 // types other than str. Check to enforce that only str can be used in
 887                 // const-eval.
 888
 889                 // const-eval of the `begin_panic` fn assumes the argument is `&str`
 890                 if Some(callee) == tcx.lang_items().begin_panic_fn() {
 891                     match args[0].ty(&self.ccx.body.local_decls, tcx).kind() {
 892                         ty::Ref(_, ty, _) if ty.is_str() => return,
 893                         _ => self.check_op(ops::PanicNonStr),
 894                     }
 895                 }
 896
 897                 // const-eval of the `panic_display` fn assumes the argument is `&&str`
 898                 if Some(callee) == tcx.lang_items().panic_display() {
 899                     match args[0].ty(&self.ccx.body.local_decls, tcx).kind() {
 900                         ty::Ref(_, ty, _) if matches!(ty.kind(), ty::Ref(_, ty, _) if ty.is_str()) =>
 901                         {
 902                             return;
 903                         }
 904                         _ => self.check_op(ops::PanicNonStr),
 905                     }
 906                 }
 907
 908                 if Some(callee) == tcx.lang_items().exchange_malloc_fn() {
 909                     self.check_op(ops::HeapAllocation);
 910                     return;
 911                 }
 912
 913                 // `async` blocks get lowered to `std::future::from_generator(/* a closure */)`.
 914                 let is_async_block = Some(callee) == tcx.lang_items().from_generator_fn();
 915                 if is_async_block {
 916                     let kind = hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Block);
 917                     self.check_op(ops::Generator(kind));
 918                     return;
 919                 }
 920
 921                 let is_intrinsic = tcx.fn_sig(callee).abi() == RustIntrinsic;
 922
 923                 if !tcx.is_const_fn_raw(callee) {
 924                     if tcx.trait_of_item(callee).is_some() {
 925                         if tcx.has_attr(callee, sym::default_method_body_is_const) {
 926                             // To get to here we must have already found a const impl for the
 927                             // trait, but for it to still be non-const can be that the impl is
 928                             // using default method bodies.
 929                             nonconst_call_permission = true;
 930                         }
 931                     }
 932
 933                     if !nonconst_call_permission {
 934                         self.check_op(ops::FnCallNonConst);
 935                         return;
 936                     }
 937                 }
 938
 939                 // If the `const fn` we are trying to call is not const-stable, ensure that we have
 940                 // the proper feature gate enabled.
 941                 if let Some(gate) = is_unstable_const_fn(tcx, callee) {
 942                     trace!(?gate, "calling unstable const fn");
 943                     if self.span.allows_unstable(gate) {
 944                         return;
 945                     }
 946
 947                     // Calling an unstable function *always* requires that the corresponding gate
 948                     // be enabled, even if the function has `#[rustc_allow_const_fn_unstable(the_gate)]`.
 949                     if !tcx.features().declared_lib_features.iter().any(|&(sym, _)| sym == gate) {
 950                         self.check_op(ops::FnCallUnstable(callee, Some(gate)));
 951                         return;
 952                     }
 953
 954                     // If this crate is not using stability attributes, or the caller is not claiming to be a
 955                     // stable `const fn`, that is all that is required.
 956                     if !self.ccx.is_const_stable_const_fn() {
 957                         trace!("crate not using stability attributes or caller not stably const");
 958                         return;
 959                     }
 960
 961                     // Otherwise, we are something const-stable calling a const-unstable fn.
 962
 963                     if super::rustc_allow_const_fn_unstable(tcx, caller, gate) {
 964                         trace!("rustc_allow_const_fn_unstable gate active");
 965                         return;
 966                     }
 967
 968                     self.check_op(ops::FnCallUnstable(callee, Some(gate)));
 969                     return;
 970                 }
 971
 972                 // FIXME(ecstaticmorse); For compatibility, we consider `unstable` callees that
 973                 // have no `rustc_const_stable` attributes to be const-unstable as well. This
 974                 // should be fixed later.
 975                 let callee_is_unstable_unmarked = tcx.lookup_const_stability(callee).is_none()
 976                     && tcx.lookup_stability(callee).map_or(false, |s| s.level.is_unstable());
 977                 if callee_is_unstable_unmarked {
 978                     trace!("callee_is_unstable_unmarked");
 979                     // We do not use `const` modifiers for intrinsic "functions", as intrinsics are
 980                     // `extern` funtions, and these have no way to get marked `const`. So instead we
 981                     // use `rustc_const_(un)stable` attributes to mean that the intrinsic is `const`
 982                     if self.ccx.is_const_stable_const_fn() || is_intrinsic {
 983                         self.check_op(ops::FnCallUnstable(callee, None));
 984                         return;
 985                     }
 986                 }
 987                 trace!("permitting call");
 988             }
 989
 990             // Forbid all `Drop` terminators unless the place being dropped is a local with no
 991             // projections that cannot be `NeedsNonConstDrop`.
 992             TerminatorKind::Drop { place: dropped_place, .. }
 993             | TerminatorKind::DropAndReplace { place: dropped_place, .. } => {
 994                 // If we are checking live drops after drop-elaboration, don't emit duplicate
 995                 // errors here.
 996                 if super::post_drop_elaboration::checking_enabled(self.ccx) {
 997                     return;
 998                 }
 999
1000                 let mut err_span = self.span;
1001
1002                 let ty_needs_non_const_drop = qualifs::NeedsNonConstDrop::in_any_value_of_ty(
1003                     self.ccx,
1004                     dropped_place.ty(self.body, self.tcx).ty,
1005                 );
1006
1007                 if !ty_needs_non_const_drop {
1008                     return;
1009                 }
1010
1011                 let needs_non_const_drop = if let Some(local) = dropped_place.as_local() {
1012                     // Use the span where the local was declared as the span of the drop error.
1013                     err_span = self.body.local_decls[local].source_info.span;
1014                     self.qualifs.needs_non_const_drop(self.ccx, local, location)
1015                 } else {
1016                     true
1017                 };
1018
1019                 if needs_non_const_drop {
1020                     self.check_op_spanned(
1021                         ops::LiveDrop { dropped_at: Some(terminator.source_info.span) },
1022                         err_span,
1023                     );
1024                 }
1025             }
1026
1027             TerminatorKind::InlineAsm { .. } => self.check_op(ops::InlineAsm),
1028
1029             TerminatorKind::GeneratorDrop | TerminatorKind::Yield { .. } => {
1030                 self.check_op(ops::Generator(hir::GeneratorKind::Gen))
1031             }
1032
1033             TerminatorKind::Abort => {
1034                 // Cleanup blocks are skipped for const checking (see `visit_basic_block_data`).
1035                 span_bug!(self.span, "`Abort` terminator outside of cleanup block")
1036             }
1037
1038             TerminatorKind::Assert { .. }
1039             | TerminatorKind::FalseEdge { .. }
1040             | TerminatorKind::FalseUnwind { .. }
1041             | TerminatorKind::Goto { .. }
1042             | TerminatorKind::Resume
1043             | TerminatorKind::Return
1044             | TerminatorKind::SwitchInt { .. }
1045             | TerminatorKind::Unreachable => {}
1046         }
1047     }
1048 }
1049
1050 fn check_return_ty_is_sync(tcx: TyCtxt<'tcx>, body: &Body<'tcx>, hir_id: HirId) {
1051     let ty = body.return_ty();
1052     tcx.infer_ctxt().enter(|infcx| {
1053         let cause = traits::ObligationCause::new(body.span, hir_id, traits::SharedStatic);
1054         let mut fulfillment_cx = traits::FulfillmentContext::new();
1055         let sync_def_id = tcx.require_lang_item(LangItem::Sync, Some(body.span));
1056         fulfillment_cx.register_bound(&infcx, ty::ParamEnv::empty(), ty, sync_def_id, cause);
1057         if let Err(err) = fulfillment_cx.select_all_or_error(&infcx) {
1058             infcx.report_fulfillment_errors(&err, None, false);
1059         }
1060     });
1061 }
1062
1063 fn place_as_reborrow(
1064     tcx: TyCtxt<'tcx>,
1065     body: &Body<'tcx>,
1066     place: Place<'tcx>,
1067 ) -> Option<PlaceRef<'tcx>> {
1068     match place.as_ref().last_projection() {
1069         Some((place_base, ProjectionElem::Deref)) => {
1070             // A borrow of a `static` also looks like `&(*_1)` in the MIR, but `_1` is a `const`
1071             // that points to the allocation for the static. Don't treat these as reborrows.
1072             if body.local_decls[place_base.local].is_ref_to_static() {
1073                 None
1074             } else {
1075                 // Ensure the type being derefed is a reference and not a raw pointer.
1076                 // This is sufficient to prevent an access to a `static mut` from being marked as a
1077                 // reborrow, even if the check above were to disappear.
1078                 let inner_ty = place_base.ty(body, tcx).ty;
1079
1080                 if let ty::Ref(..) = inner_ty.kind() {
1081                     return Some(place_base);
1082                 } else {
1083                     return None;
1084                 }
1085             }
1086         }
1087         _ => None,
1088     }
1089 }
1090
1091 fn is_int_bool_or_char(ty: Ty<'_>) -> bool {
1092     ty.is_bool() || ty.is_integral() || ty.is_char()
1093 }
1094
1095 fn is_async_fn(ccx: &ConstCx<'_, '_>) -> bool {
1096     ccx.fn_sig().map_or(false, |sig| sig.header.asyncness == hir::IsAsync::Async)
1097 }
1098
1099 fn emit_unstable_in_stable_error(ccx: &ConstCx<'_, '_>, span: Span, gate: Symbol) {
1100     let attr_span = ccx.fn_sig().map_or(ccx.body.span, |sig| sig.span.shrink_to_lo());
1101
1102     ccx.tcx
1103         .sess
1104         .struct_span_err(
1105             span,
1106             &format!("const-stable function cannot use `#[feature({})]`", gate.as_str()),
1107         )
1108         .span_suggestion(
1109             attr_span,
1110             "if it is not part of the public API, make this function unstably const",
1111             concat!(r#"#[rustc_const_unstable(feature = "...", issue = "...")]"#, '\n').to_owned(),
1112             Applicability::HasPlaceholders,
1113         )
1114         .span_suggestion(
1115             attr_span,
1116             "otherwise `#[rustc_allow_const_fn_unstable]` can be used to bypass stability checks",
1117             format!("#[rustc_allow_const_fn_unstable({})]\n", gate),
1118             Applicability::MaybeIncorrect,
1119         )
1120         .emit();
1121 }