src/librustc_mir/transform/check_consts/validation.rs

   1 //! The `Visitor` responsible for actually checking a `mir::Body` for invalid operations.
   2
   3 use rustc_errors::struct_span_err;
   4 use rustc_hir::lang_items;
   5 use rustc_hir::{def_id::DefId, HirId};
   6 use rustc_index::bit_set::BitSet;
   7 use rustc_infer::infer::TyCtxtInferExt;
   8 use rustc_middle::mir::visit::{MutatingUseContext, NonMutatingUseContext, PlaceContext, Visitor};
   9 use rustc_middle::mir::*;
  10 use rustc_middle::ty::cast::CastTy;
  11 use rustc_middle::ty::{self, Instance, InstanceDef, TyCtxt};
  12 use rustc_span::symbol::sym;
  13 use rustc_span::Span;
  14 use rustc_trait_selection::traits::error_reporting::InferCtxtExt;
  15 use rustc_trait_selection::traits::{self, TraitEngine};
  16
  17 use std::borrow::Cow;
  18 use std::ops::Deref;
  19
  20 use super::ops::{self, NonConstOp};
  21 use super::qualifs::{self, HasMutInterior, NeedsDrop};
  22 use super::resolver::FlowSensitiveAnalysis;
  23 use super::{is_lang_panic_fn, ConstCx, ConstKind, Qualif};
  24 use crate::const_eval::{is_const_fn, is_unstable_const_fn};
  25 use crate::dataflow::MaybeMutBorrowedLocals;
  26 use crate::dataflow::{self, Analysis};
  27
  28 // We are using `MaybeMutBorrowedLocals` as a proxy for whether an item may have been mutated
  29 // through a pointer prior to the given point. This is okay even though `MaybeMutBorrowedLocals`
  30 // kills locals upon `StorageDead` because a local will never be used after a `StorageDead`.
  31 pub type IndirectlyMutableResults<'mir, 'tcx> =
  32     dataflow::ResultsCursor<'mir, 'tcx, MaybeMutBorrowedLocals<'mir, 'tcx>>;
  33
  34 struct QualifCursor<'a, 'mir, 'tcx, Q: Qualif> {
  35     cursor: dataflow::ResultsCursor<'mir, 'tcx, FlowSensitiveAnalysis<'a, 'mir, 'tcx, Q>>,
  36     in_any_value_of_ty: BitSet<Local>,
  37 }
  38
  39 impl<Q: Qualif> QualifCursor<'a, 'mir, 'tcx, Q> {
  40     pub fn new(q: Q, ccx: &'a ConstCx<'mir, 'tcx>) -> Self {
  41         let cursor = FlowSensitiveAnalysis::new(q, ccx)
  42             .into_engine(ccx.tcx, ccx.body, ccx.def_id)
  43             .iterate_to_fixpoint()
  44             .into_results_cursor(ccx.body);
  45
  46         let mut in_any_value_of_ty = BitSet::new_empty(ccx.body.local_decls.len());
  47         for (local, decl) in ccx.body.local_decls.iter_enumerated() {
  48             if Q::in_any_value_of_ty(ccx, decl.ty) {
  49                 in_any_value_of_ty.insert(local);
  50             }
  51         }
  52
  53         QualifCursor { cursor, in_any_value_of_ty }
  54     }
  55 }
  56
  57 pub struct Qualifs<'a, 'mir, 'tcx> {
  58     has_mut_interior: QualifCursor<'a, 'mir, 'tcx, HasMutInterior>,
  59     needs_drop: QualifCursor<'a, 'mir, 'tcx, NeedsDrop>,
  60     indirectly_mutable: IndirectlyMutableResults<'mir, 'tcx>,
  61 }
  62
  63 impl Qualifs<'a, 'mir, 'tcx> {
  64     fn indirectly_mutable(&mut self, local: Local, location: Location) -> bool {
  65         self.indirectly_mutable.seek_before(location);
  66         self.indirectly_mutable.get().contains(local)
  67     }
  68
  69     /// Returns `true` if `local` is `NeedsDrop` at the given `Location`.
  70     ///
  71     /// Only updates the cursor if absolutely necessary
  72     fn needs_drop(&mut self, local: Local, location: Location) -> bool {
  73         if !self.needs_drop.in_any_value_of_ty.contains(local) {
  74             return false;
  75         }
  76
  77         self.needs_drop.cursor.seek_before(location);
  78         self.needs_drop.cursor.get().contains(local) || self.indirectly_mutable(local, location)
  79     }
  80
  81     /// Returns `true` if `local` is `HasMutInterior` at the given `Location`.
  82     ///
  83     /// Only updates the cursor if absolutely necessary.
  84     fn has_mut_interior(&mut self, local: Local, location: Location) -> bool {
  85         if !self.has_mut_interior.in_any_value_of_ty.contains(local) {
  86             return false;
  87         }
  88
  89         self.has_mut_interior.cursor.seek_before(location);
  90         self.has_mut_interior.cursor.get().contains(local)
  91             || self.indirectly_mutable(local, location)
  92     }
  93
  94     fn in_return_place(&mut self, ccx: &ConstCx<'_, 'tcx>) -> ConstQualifs {
  95         // Find the `Return` terminator if one exists.
  96         //
  97         // If no `Return` terminator exists, this MIR is divergent. Just return the conservative
  98         // qualifs for the return type.
  99         let return_block = ccx
 100             .body
 101             .basic_blocks()
 102             .iter_enumerated()
 103             .find(|(_, block)| match block.terminator().kind {
 104                 TerminatorKind::Return => true,
 105                 _ => false,
 106             })
 107             .map(|(bb, _)| bb);
 108
 109         let return_block = match return_block {
 110             None => return qualifs::in_any_value_of_ty(ccx, ccx.body.return_ty()),
 111             Some(bb) => bb,
 112         };
 113
 114         let return_loc = ccx.body.terminator_loc(return_block);
 115
 116         ConstQualifs {
 117             needs_drop: self.needs_drop(RETURN_PLACE, return_loc),
 118             has_mut_interior: self.has_mut_interior(RETURN_PLACE, return_loc),
 119         }
 120     }
 121 }
 122
 123 pub struct Validator<'a, 'mir, 'tcx> {
 124     ccx: &'a ConstCx<'mir, 'tcx>,
 125     qualifs: Qualifs<'a, 'mir, 'tcx>,
 126
 127     /// The span of the current statement.
 128     span: Span,
 129 }
 130
 131 impl Deref for Validator<'_, 'mir, 'tcx> {
 132     type Target = ConstCx<'mir, 'tcx>;
 133
 134     fn deref(&self) -> &Self::Target {
 135         &self.ccx
 136     }
 137 }
 138
 139 impl Validator<'a, 'mir, 'tcx> {
 140     pub fn new(ccx: &'a ConstCx<'mir, 'tcx>) -> Self {
 141         let ConstCx { tcx, body, def_id, param_env, .. } = *ccx;
 142
 143         let needs_drop = QualifCursor::new(NeedsDrop, ccx);
 144         let has_mut_interior = QualifCursor::new(HasMutInterior, ccx);
 145
 146         // We can use `unsound_ignore_borrow_on_drop` here because custom drop impls are not
 147         // allowed in a const.
 148         //
 149         // FIXME(ecstaticmorse): Someday we want to allow custom drop impls. How do we do this
 150         // without breaking stable code?
 151         let indirectly_mutable = MaybeMutBorrowedLocals::mut_borrows_only(tcx, body, param_env)
 152             .unsound_ignore_borrow_on_drop()
 153             .into_engine(tcx, body, def_id)
 154             .iterate_to_fixpoint()
 155             .into_results_cursor(body);
 156
 157         let qualifs = Qualifs { needs_drop, has_mut_interior, indirectly_mutable };
 158
 159         Validator { span: ccx.body.span, ccx, qualifs }
 160     }
 161
 162     pub fn check_body(&mut self) {
 163         let ConstCx { tcx, body, def_id, const_kind, .. } = *self.ccx;
 164
 165         let use_min_const_fn_checks = (const_kind == Some(ConstKind::ConstFn)
 166             && crate::const_eval::is_min_const_fn(tcx, def_id))
 167             && !tcx.sess.opts.debugging_opts.unleash_the_miri_inside_of_you;
 168
 169         if use_min_const_fn_checks {
 170             // Enforce `min_const_fn` for stable `const fn`s.
 171             use crate::transform::qualify_min_const_fn::is_min_const_fn;
 172             if let Err((span, err)) = is_min_const_fn(tcx, def_id, &body) {
 173                 error_min_const_fn_violation(tcx, span, err);
 174                 return;
 175             }
 176         }
 177
 178         check_short_circuiting_in_const_local(self.ccx);
 179
 180         if body.is_cfg_cyclic() {
 181             // We can't provide a good span for the error here, but this should be caught by the
 182             // HIR const-checker anyways.
 183             self.check_op_spanned(ops::Loop, body.span);
 184         }
 185
 186         self.visit_body(&body);
 187
 188         // Ensure that the end result is `Sync` in a non-thread local `static`.
 189         let should_check_for_sync =
 190             const_kind == Some(ConstKind::Static) && !tcx.has_attr(def_id, sym::thread_local);
 191
 192         if should_check_for_sync {
 193             let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
 194             check_return_ty_is_sync(tcx, &body, hir_id);
 195         }
 196     }
 197
 198     pub fn qualifs_in_return_place(&mut self) -> ConstQualifs {
 199         self.qualifs.in_return_place(self.ccx)
 200     }
 201
 202     /// Emits an error at the given `span` if an expression cannot be evaluated in the current
 203     /// context.
 204     pub fn check_op_spanned<O>(&mut self, op: O, span: Span)
 205     where
 206         O: NonConstOp,
 207     {
 208         trace!("check_op: op={:?}", op);
 209
 210         if op.is_allowed_in_item(self) {
 211             return;
 212         }
 213
 214         // If an operation is supported in miri (and is not already controlled by a feature gate) it
 215         // can be turned on with `-Zunleash-the-miri-inside-of-you`.
 216         let is_unleashable = O::IS_SUPPORTED_IN_MIRI && O::feature_gate().is_none();
 217
 218         if is_unleashable && self.tcx.sess.opts.debugging_opts.unleash_the_miri_inside_of_you {
 219             self.tcx.sess.span_warn(span, "skipping const checks");
 220             return;
 221         }
 222
 223         op.emit_error(self, span);
 224     }
 225
 226     /// Emits an error if an expression cannot be evaluated in the current context.
 227     pub fn check_op(&mut self, op: impl NonConstOp) {
 228         let span = self.span;
 229         self.check_op_spanned(op, span)
 230     }
 231
 232     fn check_static(&mut self, def_id: DefId, span: Span) {
 233         let is_thread_local = self.tcx.has_attr(def_id, sym::thread_local);
 234         if is_thread_local {
 235             self.check_op_spanned(ops::ThreadLocalAccess, span)
 236         } else {
 237             self.check_op_spanned(ops::StaticAccess, span)
 238         }
 239     }
 240 }
 241
 242 impl Visitor<'tcx> for Validator<'_, 'mir, 'tcx> {
 243     fn visit_basic_block_data(&mut self, bb: BasicBlock, block: &BasicBlockData<'tcx>) {
 244         trace!("visit_basic_block_data: bb={:?} is_cleanup={:?}", bb, block.is_cleanup);
 245
 246         // Just as the old checker did, we skip const-checking basic blocks on the unwind path.
 247         // These blocks often drop locals that would otherwise be returned from the function.
 248         //
 249         // FIXME: This shouldn't be unsound since a panic at compile time will cause a compiler
 250         // error anyway, but maybe we should do more here?
 251         if block.is_cleanup {
 252             return;
 253         }
 254
 255         self.super_basic_block_data(bb, block);
 256     }
 257
 258     fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, location: Location) {
 259         trace!("visit_rvalue: rvalue={:?} location={:?}", rvalue, location);
 260
 261         // Special-case reborrows to be more like a copy of a reference.
 262         match *rvalue {
 263             Rvalue::Ref(_, kind, place) => {
 264                 if let Some(reborrowed_proj) = place_as_reborrow(self.tcx, self.body, place) {
 265                     let ctx = match kind {
 266                         BorrowKind::Shared => {
 267                             PlaceContext::NonMutatingUse(NonMutatingUseContext::SharedBorrow)
 268                         }
 269                         BorrowKind::Shallow => {
 270                             PlaceContext::NonMutatingUse(NonMutatingUseContext::ShallowBorrow)
 271                         }
 272                         BorrowKind::Unique => {
 273                             PlaceContext::NonMutatingUse(NonMutatingUseContext::UniqueBorrow)
 274                         }
 275                         BorrowKind::Mut { .. } => {
 276                             PlaceContext::MutatingUse(MutatingUseContext::Borrow)
 277                         }
 278                     };
 279                     self.visit_local(&place.local, ctx, location);
 280                     self.visit_projection(place.local, reborrowed_proj, ctx, location);
 281                     return;
 282                 }
 283             }
 284             Rvalue::AddressOf(mutbl, place) => {
 285                 if let Some(reborrowed_proj) = place_as_reborrow(self.tcx, self.body, place) {
 286                     let ctx = match mutbl {
 287                         Mutability::Not => {
 288                             PlaceContext::NonMutatingUse(NonMutatingUseContext::AddressOf)
 289                         }
 290                         Mutability::Mut => PlaceContext::MutatingUse(MutatingUseContext::AddressOf),
 291                     };
 292                     self.visit_local(&place.local, ctx, location);
 293                     self.visit_projection(place.local, reborrowed_proj, ctx, location);
 294                     return;
 295                 }
 296             }
 297             _ => {}
 298         }
 299
 300         self.super_rvalue(rvalue, location);
 301
 302         match *rvalue {
 303             Rvalue::Use(_)
 304             | Rvalue::Repeat(..)
 305             | Rvalue::UnaryOp(UnOp::Neg, _)
 306             | Rvalue::UnaryOp(UnOp::Not, _)
 307             | Rvalue::NullaryOp(NullOp::SizeOf, _)
 308             | Rvalue::CheckedBinaryOp(..)
 309             | Rvalue::Cast(CastKind::Pointer(_), ..)
 310             | Rvalue::Discriminant(..)
 311             | Rvalue::Len(_)
 312             | Rvalue::Aggregate(..) => {}
 313
 314             Rvalue::Ref(_, kind @ BorrowKind::Mut { .. }, ref place)
 315             | Rvalue::Ref(_, kind @ BorrowKind::Unique, ref place) => {
 316                 let ty = place.ty(self.body, self.tcx).ty;
 317                 let is_allowed = match ty.kind {
 318                     // Inside a `static mut`, `&mut [...]` is allowed.
 319                     ty::Array(..) | ty::Slice(_) if self.const_kind() == ConstKind::StaticMut => {
 320                         true
 321                     }
 322
 323                     // FIXME(ecstaticmorse): We could allow `&mut []` inside a const context given
 324                     // that this is merely a ZST and it is already eligible for promotion.
 325                     // This may require an RFC?
 326                     /*
 327                     ty::Array(_, len) if len.try_eval_usize(cx.tcx, cx.param_env) == Some(0)
 328                         => true,
 329                     */
 330                     _ => false,
 331                 };
 332
 333                 if !is_allowed {
 334                     if let BorrowKind::Mut { .. } = kind {
 335                         self.check_op(ops::MutBorrow);
 336                     } else {
 337                         self.check_op(ops::CellBorrow);
 338                     }
 339                 }
 340             }
 341
 342             Rvalue::AddressOf(Mutability::Mut, _) => self.check_op(ops::MutAddressOf),
 343
 344             Rvalue::Ref(_, BorrowKind::Shared | BorrowKind::Shallow, ref place)
 345             | Rvalue::AddressOf(Mutability::Not, ref place) => {
 346                 let borrowed_place_has_mut_interior = qualifs::in_place::<HasMutInterior, _>(
 347                     &self.ccx,
 348                     &mut |local| self.qualifs.has_mut_interior(local, location),
 349                     place.as_ref(),
 350                 );
 351
 352                 if borrowed_place_has_mut_interior {
 353                     self.check_op(ops::CellBorrow);
 354                 }
 355             }
 356
 357             Rvalue::Cast(CastKind::Misc, ref operand, cast_ty) => {
 358                 let operand_ty = operand.ty(self.body, self.tcx);
 359                 let cast_in = CastTy::from_ty(operand_ty).expect("bad input type for cast");
 360                 let cast_out = CastTy::from_ty(cast_ty).expect("bad output type for cast");
 361
 362                 if let (CastTy::Ptr(_) | CastTy::FnPtr, CastTy::Int(_)) = (cast_in, cast_out) {
 363                     self.check_op(ops::RawPtrToIntCast);
 364                 }
 365             }
 366
 367             Rvalue::BinaryOp(op, ref lhs, _) => {
 368                 if let ty::RawPtr(_) | ty::FnPtr(..) = lhs.ty(self.body, self.tcx).kind {
 369                     assert!(
 370                         op == BinOp::Eq
 371                             || op == BinOp::Ne
 372                             || op == BinOp::Le
 373                             || op == BinOp::Lt
 374                             || op == BinOp::Ge
 375                             || op == BinOp::Gt
 376                             || op == BinOp::Offset
 377                     );
 378
 379                     self.check_op(ops::RawPtrComparison);
 380                 }
 381             }
 382
 383             Rvalue::NullaryOp(NullOp::Box, _) => {
 384                 self.check_op(ops::HeapAllocation);
 385             }
 386         }
 387     }
 388
 389     fn visit_local(&mut self, place_local: &Local, context: PlaceContext, location: Location) {
 390         trace!(
 391             "visit_local: place_local={:?} context={:?} location={:?}",
 392             place_local,
 393             context,
 394             location,
 395         );
 396     }
 397
 398     fn visit_operand(&mut self, op: &Operand<'tcx>, location: Location) {
 399         self.super_operand(op, location);
 400         if let Operand::Constant(c) = op {
 401             if let Some(def_id) = c.check_static_ptr(self.tcx) {
 402                 self.check_static(def_id, self.span);
 403             }
 404         }
 405     }
 406     fn visit_projection_elem(
 407         &mut self,
 408         place_local: Local,
 409         proj_base: &[PlaceElem<'tcx>],
 410         elem: &PlaceElem<'tcx>,
 411         context: PlaceContext,
 412         location: Location,
 413     ) {
 414         trace!(
 415             "visit_projection_elem: place_local={:?} proj_base={:?} elem={:?} \
 416             context={:?} location={:?}",
 417             place_local,
 418             proj_base,
 419             elem,
 420             context,
 421             location,
 422         );
 423
 424         self.super_projection_elem(place_local, proj_base, elem, context, location);
 425
 426         match elem {
 427             ProjectionElem::Deref => {
 428                 let base_ty = Place::ty_from(place_local, proj_base, self.body, self.tcx).ty;
 429                 if let ty::RawPtr(_) = base_ty.kind {
 430                     if proj_base.is_empty() {
 431                         if let (local, []) = (place_local, proj_base) {
 432                             let decl = &self.body.local_decls[local];
 433                             if let LocalInfo::StaticRef { def_id, .. } = decl.local_info {
 434                                 let span = decl.source_info.span;
 435                                 self.check_static(def_id, span);
 436                                 return;
 437                             }
 438                         }
 439                     }
 440                     self.check_op(ops::RawPtrDeref);
 441                 }
 442
 443                 if context.is_mutating_use() {
 444                     self.check_op(ops::MutDeref);
 445                 }
 446             }
 447
 448             ProjectionElem::ConstantIndex { .. }
 449             | ProjectionElem::Subslice { .. }
 450             | ProjectionElem::Field(..)
 451             | ProjectionElem::Index(_) => {
 452                 let base_ty = Place::ty_from(place_local, proj_base, self.body, self.tcx).ty;
 453                 match base_ty.ty_adt_def() {
 454                     Some(def) if def.is_union() => {
 455                         self.check_op(ops::UnionAccess);
 456                     }
 457
 458                     _ => {}
 459                 }
 460             }
 461
 462             ProjectionElem::Downcast(..) => {
 463                 self.check_op(ops::Downcast);
 464             }
 465         }
 466     }
 467
 468     fn visit_source_info(&mut self, source_info: &SourceInfo) {
 469         trace!("visit_source_info: source_info={:?}", source_info);
 470         self.span = source_info.span;
 471     }
 472
 473     fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) {
 474         trace!("visit_statement: statement={:?} location={:?}", statement, location);
 475
 476         match statement.kind {
 477             StatementKind::Assign(..) | StatementKind::SetDiscriminant { .. } => {
 478                 self.super_statement(statement, location);
 479             }
 480
 481             StatementKind::FakeRead(
 482                 FakeReadCause::ForMatchedPlace
 483                 | FakeReadCause::ForMatchGuard
 484                 | FakeReadCause::ForGuardBinding,
 485                 _,
 486             ) => {
 487                 self.super_statement(statement, location);
 488                 self.check_op(ops::IfOrMatch);
 489             }
 490             StatementKind::LlvmInlineAsm { .. } => {
 491                 self.super_statement(statement, location);
 492                 self.check_op(ops::InlineAsm);
 493             }
 494
 495             StatementKind::FakeRead(FakeReadCause::ForLet | FakeReadCause::ForIndex, _)
 496             | StatementKind::StorageLive(_)
 497             | StatementKind::StorageDead(_)
 498             | StatementKind::Retag { .. }
 499             | StatementKind::AscribeUserType(..)
 500             | StatementKind::Nop => {}
 501         }
 502     }
 503
 504     fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location) {
 505         trace!("visit_terminator: terminator={:?} location={:?}", terminator, location);
 506         self.super_terminator(terminator, location);
 507
 508         match &terminator.kind {
 509             TerminatorKind::Call { func, .. } => {
 510                 let fn_ty = func.ty(self.body, self.tcx);
 511
 512                 let (def_id, substs) = match fn_ty.kind {
 513                     ty::FnDef(def_id, substs) => (def_id, substs),
 514
 515                     ty::FnPtr(_) => {
 516                         self.check_op(ops::FnCallIndirect);
 517                         return;
 518                     }
 519                     _ => {
 520                         span_bug!(terminator.source_info.span, "invalid callee of type {:?}", fn_ty)
 521                     }
 522                 };
 523
 524                 // At this point, we are calling a function whose `DefId` is known...
 525                 if is_const_fn(self.tcx, def_id) {
 526                     return;
 527                 }
 528
 529                 // See if this is a trait method for a concrete type whose impl of that trait is
 530                 // `const`.
 531                 if self.tcx.features().const_trait_impl {
 532                     let instance = Instance::resolve(self.tcx, self.param_env, def_id, substs);
 533                     debug!("Resolving ({:?}) -> {:?}", def_id, instance);
 534                     if let Ok(Some(func)) = instance {
 535                         if let InstanceDef::Item(def_id) = func.def {
 536                             if is_const_fn(self.tcx, def_id) {
 537                                 return;
 538                             }
 539                         }
 540                     }
 541                 }
 542
 543                 if is_lang_panic_fn(self.tcx, def_id) {
 544                     self.check_op(ops::Panic);
 545                 } else if let Some(feature) = is_unstable_const_fn(self.tcx, def_id) {
 546                     // Exempt unstable const fns inside of macros with
 547                     // `#[allow_internal_unstable]`.
 548                     if !self.span.allows_unstable(feature) {
 549                         self.check_op(ops::FnCallUnstable(def_id, feature));
 550                     }
 551                 } else {
 552                     self.check_op(ops::FnCallNonConst(def_id));
 553                 }
 554             }
 555
 556             // Forbid all `Drop` terminators unless the place being dropped is a local with no
 557             // projections that cannot be `NeedsDrop`.
 558             TerminatorKind::Drop { location: dropped_place, .. }
 559             | TerminatorKind::DropAndReplace { location: dropped_place, .. } => {
 560                 let mut err_span = self.span;
 561
 562                 // Check to see if the type of this place can ever have a drop impl. If not, this
 563                 // `Drop` terminator is frivolous.
 564                 let ty_needs_drop =
 565                     dropped_place.ty(self.body, self.tcx).ty.needs_drop(self.tcx, self.param_env);
 566
 567                 if !ty_needs_drop {
 568                     return;
 569                 }
 570
 571                 let needs_drop = if let Some(local) = dropped_place.as_local() {
 572                     // Use the span where the local was declared as the span of the drop error.
 573                     err_span = self.body.local_decls[local].source_info.span;
 574                     self.qualifs.needs_drop(local, location)
 575                 } else {
 576                     true
 577                 };
 578
 579                 if needs_drop {
 580                     self.check_op_spanned(ops::LiveDrop, err_span);
 581                 }
 582             }
 583
 584             // FIXME: Some of these are only caught by `min_const_fn`, but should error here
 585             // instead.
 586             TerminatorKind::Abort
 587             | TerminatorKind::Assert { .. }
 588             | TerminatorKind::FalseEdges { .. }
 589             | TerminatorKind::FalseUnwind { .. }
 590             | TerminatorKind::GeneratorDrop
 591             | TerminatorKind::Goto { .. }
 592             | TerminatorKind::Resume
 593             | TerminatorKind::Return
 594             | TerminatorKind::SwitchInt { .. }
 595             | TerminatorKind::Unreachable
 596             | TerminatorKind::Yield { .. } => {}
 597         }
 598     }
 599 }
 600
 601 fn error_min_const_fn_violation(tcx: TyCtxt<'_>, span: Span, msg: Cow<'_, str>) {
 602     struct_span_err!(tcx.sess, span, E0723, "{}", msg)
 603         .note(
 604             "see issue #57563 <https://github.com/rust-lang/rust/issues/57563> \
 605              for more information",
 606         )
 607         .help("add `#![feature(const_fn)]` to the crate attributes to enable")
 608         .emit();
 609 }
 610
 611 fn check_short_circuiting_in_const_local(ccx: &ConstCx<'_, 'tcx>) {
 612     let body = ccx.body;
 613
 614     if body.control_flow_destroyed.is_empty() {
 615         return;
 616     }
 617
 618     let mut locals = body.vars_iter();
 619     if let Some(local) = locals.next() {
 620         let span = body.local_decls[local].source_info.span;
 621         let mut error = ccx.tcx.sess.struct_span_err(
 622             span,
 623             &format!(
 624                 "new features like let bindings are not permitted in {}s \
 625                 which also use short circuiting operators",
 626                 ccx.const_kind(),
 627             ),
 628         );
 629         for (span, kind) in body.control_flow_destroyed.iter() {
 630             error.span_note(
 631                 *span,
 632                 &format!(
 633                     "use of {} here does not actually short circuit due to \
 634                      the const evaluator presently not being able to do control flow. \
 635                      See issue #49146 <https://github.com/rust-lang/rust/issues/49146> \
 636                      for more information.",
 637                     kind
 638                 ),
 639             );
 640         }
 641         for local in locals {
 642             let span = body.local_decls[local].source_info.span;
 643             error.span_note(span, "more locals are defined here");
 644         }
 645         error.emit();
 646     }
 647 }
 648
 649 fn check_return_ty_is_sync(tcx: TyCtxt<'tcx>, body: &Body<'tcx>, hir_id: HirId) {
 650     let ty = body.return_ty();
 651     tcx.infer_ctxt().enter(|infcx| {
 652         let cause = traits::ObligationCause::new(body.span, hir_id, traits::SharedStatic);
 653         let mut fulfillment_cx = traits::FulfillmentContext::new();
 654         let sync_def_id = tcx.require_lang_item(lang_items::SyncTraitLangItem, Some(body.span));
 655         fulfillment_cx.register_bound(&infcx, ty::ParamEnv::empty(), ty, sync_def_id, cause);
 656         if let Err(err) = fulfillment_cx.select_all_or_error(&infcx) {
 657             infcx.report_fulfillment_errors(&err, None, false);
 658         }
 659     });
 660 }
 661
 662 fn place_as_reborrow(
 663     tcx: TyCtxt<'tcx>,
 664     body: &Body<'tcx>,
 665     place: Place<'tcx>,
 666 ) -> Option<&'a [PlaceElem<'tcx>]> {
 667     place.projection.split_last().and_then(|(outermost, inner)| {
 668         if outermost != &ProjectionElem::Deref {
 669             return None;
 670         }
 671
 672         // A borrow of a `static` also looks like `&(*_1)` in the MIR, but `_1` is a `const`
 673         // that points to the allocation for the static. Don't treat these as reborrows.
 674         if body.local_decls[place.local].is_ref_to_static() {
 675             return None;
 676         }
 677
 678         // Ensure the type being derefed is a reference and not a raw pointer.
 679         //
 680         // This is sufficient to prevent an access to a `static mut` from being marked as a
 681         // reborrow, even if the check above were to disappear.
 682         let inner_ty = Place::ty_from(place.local, inner, body, tcx).ty;
 683         match inner_ty.kind {
 684             ty::Ref(..) => Some(inner),
 685             _ => None,
 686         }
 687     })
 688 }