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