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_infer::infer::TyCtxtInferExt;
   7 use rustc_middle::mir::visit::{MutatingUseContext, NonMutatingUseContext, PlaceContext, Visitor};
   8 use rustc_middle::mir::*;
   9 use rustc_middle::ty::cast::CastTy;
  10 use rustc_middle::ty::{self, Instance, InstanceDef, TyCtxt};
  11 use rustc_span::symbol::sym;
  12 use rustc_span::Span;
  13 use rustc_trait_selection::traits::error_reporting::InferCtxtExt;
  14 use rustc_trait_selection::traits::{self, TraitEngine};
  15
  16 use std::borrow::Cow;
  17 use std::ops::Deref;
  18
  19 use super::ops::{self, NonConstOp};
  20 use super::qualifs::{self, HasMutInterior, NeedsDrop};
  21 use super::resolver::FlowSensitiveAnalysis;
  22 use super::{is_lang_panic_fn, ConstCx, ConstKind, Qualif};
  23 use crate::const_eval::{is_const_fn, is_unstable_const_fn};
  24 use crate::dataflow::MaybeMutBorrowedLocals;
  25 use crate::dataflow::{self, Analysis};
  26
  27 // We are using `MaybeMutBorrowedLocals` as a proxy for whether an item may have been mutated
  28 // through a pointer prior to the given point. This is okay even though `MaybeMutBorrowedLocals`
  29 // kills locals upon `StorageDead` because a local will never be used after a `StorageDead`.
  30 type IndirectlyMutableResults<'mir, 'tcx> =
  31     dataflow::ResultsCursor<'mir, 'tcx, MaybeMutBorrowedLocals<'mir, 'tcx>>;
  32
  33 type QualifResults<'mir, 'tcx, Q> =
  34     dataflow::ResultsCursor<'mir, 'tcx, FlowSensitiveAnalysis<'mir, 'mir, 'tcx, Q>>;
  35
  36 #[derive(Default)]
  37 pub struct Qualifs<'mir, 'tcx> {
  38     has_mut_interior: Option<QualifResults<'mir, 'tcx, HasMutInterior>>,
  39     needs_drop: Option<QualifResults<'mir, 'tcx, NeedsDrop>>,
  40     indirectly_mutable: Option<IndirectlyMutableResults<'mir, 'tcx>>,
  41 }
  42
  43 impl Qualifs<'mir, 'tcx> {
  44     fn indirectly_mutable(
  45         &mut self,
  46         ccx: &'mir ConstCx<'mir, 'tcx>,
  47         local: Local,
  48         location: Location,
  49     ) -> bool {
  50         let indirectly_mutable = self.indirectly_mutable.get_or_insert_with(|| {
  51             let ConstCx { tcx, body, def_id, param_env, .. } = *ccx;
  52
  53             // We can use `unsound_ignore_borrow_on_drop` here because custom drop impls are not
  54             // allowed in a const.
  55             //
  56             // FIXME(ecstaticmorse): Someday we want to allow custom drop impls. How do we do this
  57             // without breaking stable code?
  58             MaybeMutBorrowedLocals::mut_borrows_only(tcx, &body, param_env)
  59                 .unsound_ignore_borrow_on_drop()
  60                 .into_engine(tcx, &body, def_id)
  61                 .iterate_to_fixpoint()
  62                 .into_results_cursor(&body)
  63         });
  64
  65         indirectly_mutable.seek_before(location);
  66         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(
  73         &mut self,
  74         ccx: &'mir ConstCx<'mir, 'tcx>,
  75         local: Local,
  76         location: Location,
  77     ) -> bool {
  78         let ty = ccx.body.local_decls[local].ty;
  79         if !NeedsDrop::in_any_value_of_ty(ccx, ty) {
  80             return false;
  81         }
  82
  83         let needs_drop = self.needs_drop.get_or_insert_with(|| {
  84             let ConstCx { tcx, body, def_id, .. } = *ccx;
  85
  86             FlowSensitiveAnalysis::new(NeedsDrop, ccx)
  87                 .into_engine(tcx, &body, def_id)
  88                 .iterate_to_fixpoint()
  89                 .into_results_cursor(&body)
  90         });
  91
  92         needs_drop.seek_before(location);
  93         needs_drop.get().contains(local) || self.indirectly_mutable(ccx, local, location)
  94     }
  95
  96     /// Returns `true` if `local` is `HasMutInterior` at the given `Location`.
  97     ///
  98     /// Only updates the cursor if absolutely necessary.
  99     fn has_mut_interior(
 100         &mut self,
 101         ccx: &'mir ConstCx<'mir, 'tcx>,
 102         local: Local,
 103         location: Location,
 104     ) -> bool {
 105         let ty = ccx.body.local_decls[local].ty;
 106         if !HasMutInterior::in_any_value_of_ty(ccx, ty) {
 107             return false;
 108         }
 109
 110         let has_mut_interior = self.has_mut_interior.get_or_insert_with(|| {
 111             let ConstCx { tcx, body, def_id, .. } = *ccx;
 112
 113             FlowSensitiveAnalysis::new(HasMutInterior, ccx)
 114                 .into_engine(tcx, &body, def_id)
 115                 .iterate_to_fixpoint()
 116                 .into_results_cursor(&body)
 117         });
 118
 119         has_mut_interior.seek_before(location);
 120         has_mut_interior.get().contains(local) || self.indirectly_mutable(ccx, local, location)
 121     }
 122
 123     fn in_return_place(&mut self, ccx: &'mir ConstCx<'mir, 'tcx>) -> ConstQualifs {
 124         // Find the `Return` terminator if one exists.
 125         //
 126         // If no `Return` terminator exists, this MIR is divergent. Just return the conservative
 127         // qualifs for the return type.
 128         let return_block = ccx
 129             .body
 130             .basic_blocks()
 131             .iter_enumerated()
 132             .find(|(_, block)| match block.terminator().kind {
 133                 TerminatorKind::Return => true,
 134                 _ => false,
 135             })
 136             .map(|(bb, _)| bb);
 137
 138         let return_block = match return_block {
 139             None => return qualifs::in_any_value_of_ty(ccx, ccx.body.return_ty()),
 140             Some(bb) => bb,
 141         };
 142
 143         let return_loc = ccx.body.terminator_loc(return_block);
 144
 145         ConstQualifs {
 146             needs_drop: self.needs_drop(ccx, RETURN_PLACE, return_loc),
 147             has_mut_interior: self.has_mut_interior(ccx, RETURN_PLACE, return_loc),
 148         }
 149     }
 150 }
 151
 152 pub struct Validator<'mir, 'tcx> {
 153     ccx: &'mir ConstCx<'mir, 'tcx>,
 154     qualifs: Qualifs<'mir, 'tcx>,
 155
 156     /// The span of the current statement.
 157     span: Span,
 158 }
 159
 160 impl Deref for Validator<'mir, 'tcx> {
 161     type Target = ConstCx<'mir, 'tcx>;
 162
 163     fn deref(&self) -> &Self::Target {
 164         &self.ccx
 165     }
 166 }
 167
 168 impl Validator<'mir, 'tcx> {
 169     pub fn new(ccx: &'mir ConstCx<'mir, 'tcx>) -> Self {
 170         Validator { span: ccx.body.span, ccx, qualifs: Default::default() }
 171     }
 172
 173     pub fn check_body(&mut self) {
 174         let ConstCx { tcx, body, def_id, const_kind, .. } = *self.ccx;
 175
 176         let use_min_const_fn_checks = (const_kind == Some(ConstKind::ConstFn)
 177             && crate::const_eval::is_min_const_fn(tcx, def_id))
 178             && !tcx.sess.opts.debugging_opts.unleash_the_miri_inside_of_you;
 179
 180         if use_min_const_fn_checks {
 181             // Enforce `min_const_fn` for stable `const fn`s.
 182             use crate::transform::qualify_min_const_fn::is_min_const_fn;
 183             if let Err((span, err)) = is_min_const_fn(tcx, def_id, &body) {
 184                 error_min_const_fn_violation(tcx, span, err);
 185                 return;
 186             }
 187         }
 188
 189         check_short_circuiting_in_const_local(self.ccx);
 190
 191         if body.is_cfg_cyclic() {
 192             // We can't provide a good span for the error here, but this should be caught by the
 193             // HIR const-checker anyways.
 194             self.check_op_spanned(ops::Loop, body.span);
 195         }
 196
 197         self.visit_body(&body);
 198
 199         // Ensure that the end result is `Sync` in a non-thread local `static`.
 200         let should_check_for_sync =
 201             const_kind == Some(ConstKind::Static) && !tcx.has_attr(def_id, sym::thread_local);
 202
 203         if should_check_for_sync {
 204             let hir_id = tcx.hir().as_local_hir_id(def_id.expect_local());
 205             check_return_ty_is_sync(tcx, &body, hir_id);
 206         }
 207     }
 208
 209     pub fn qualifs_in_return_place(&mut self) -> ConstQualifs {
 210         self.qualifs.in_return_place(self.ccx)
 211     }
 212
 213     /// Emits an error at the given `span` if an expression cannot be evaluated in the current
 214     /// context.
 215     pub fn check_op_spanned<O>(&mut self, op: O, span: Span)
 216     where
 217         O: NonConstOp,
 218     {
 219         debug!("check_op: op={:?}", op);
 220
 221         if op.is_allowed_in_item(self) {
 222             return;
 223         }
 224
 225         // If an operation is supported in miri (and is not already controlled by a feature gate) it
 226         // can be turned on with `-Zunleash-the-miri-inside-of-you`.
 227         let is_unleashable = O::IS_SUPPORTED_IN_MIRI && O::feature_gate().is_none();
 228
 229         if is_unleashable && self.tcx.sess.opts.debugging_opts.unleash_the_miri_inside_of_you {
 230             self.tcx.sess.span_warn(span, "skipping const checks");
 231             return;
 232         }
 233
 234         op.emit_error(self, span);
 235     }
 236
 237     /// Emits an error if an expression cannot be evaluated in the current context.
 238     pub fn check_op(&mut self, op: impl NonConstOp) {
 239         let span = self.span;
 240         self.check_op_spanned(op, span)
 241     }
 242
 243     fn check_static(&mut self, def_id: DefId, span: Span) {
 244         let is_thread_local = self.tcx.has_attr(def_id, sym::thread_local);
 245         if is_thread_local {
 246             self.check_op_spanned(ops::ThreadLocalAccess, span)
 247         } else {
 248             self.check_op_spanned(ops::StaticAccess, span)
 249         }
 250     }
 251 }
 252
 253 impl Visitor<'tcx> for Validator<'mir, 'tcx> {
 254     fn visit_basic_block_data(&mut self, bb: BasicBlock, block: &BasicBlockData<'tcx>) {
 255         trace!("visit_basic_block_data: bb={:?} is_cleanup={:?}", bb, block.is_cleanup);
 256
 257         // Just as the old checker did, we skip const-checking basic blocks on the unwind path.
 258         // These blocks often drop locals that would otherwise be returned from the function.
 259         //
 260         // FIXME: This shouldn't be unsound since a panic at compile time will cause a compiler
 261         // error anyway, but maybe we should do more here?
 262         if block.is_cleanup {
 263             return;
 264         }
 265
 266         self.super_basic_block_data(bb, block);
 267     }
 268
 269     fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, location: Location) {
 270         trace!("visit_rvalue: rvalue={:?} location={:?}", rvalue, location);
 271
 272         // Special-case reborrows to be more like a copy of a reference.
 273         match *rvalue {
 274             Rvalue::Ref(_, kind, place) => {
 275                 if let Some(reborrowed_proj) = place_as_reborrow(self.tcx, self.body, place) {
 276                     let ctx = match kind {
 277                         BorrowKind::Shared => {
 278                             PlaceContext::NonMutatingUse(NonMutatingUseContext::SharedBorrow)
 279                         }
 280                         BorrowKind::Shallow => {
 281                             PlaceContext::NonMutatingUse(NonMutatingUseContext::ShallowBorrow)
 282                         }
 283                         BorrowKind::Unique => {
 284                             PlaceContext::NonMutatingUse(NonMutatingUseContext::UniqueBorrow)
 285                         }
 286                         BorrowKind::Mut { .. } => {
 287                             PlaceContext::MutatingUse(MutatingUseContext::Borrow)
 288                         }
 289                     };
 290                     self.visit_local(&place.local, ctx, location);
 291                     self.visit_projection(place.local, reborrowed_proj, ctx, location);
 292                     return;
 293                 }
 294             }
 295             Rvalue::AddressOf(mutbl, place) => {
 296                 if let Some(reborrowed_proj) = place_as_reborrow(self.tcx, self.body, place) {
 297                     let ctx = match mutbl {
 298                         Mutability::Not => {
 299                             PlaceContext::NonMutatingUse(NonMutatingUseContext::AddressOf)
 300                         }
 301                         Mutability::Mut => PlaceContext::MutatingUse(MutatingUseContext::AddressOf),
 302                     };
 303                     self.visit_local(&place.local, ctx, location);
 304                     self.visit_projection(place.local, reborrowed_proj, ctx, location);
 305                     return;
 306                 }
 307             }
 308             _ => {}
 309         }
 310
 311         self.super_rvalue(rvalue, location);
 312
 313         match *rvalue {
 314             Rvalue::Use(_)
 315             | Rvalue::Repeat(..)
 316             | Rvalue::UnaryOp(UnOp::Neg, _)
 317             | Rvalue::UnaryOp(UnOp::Not, _)
 318             | Rvalue::NullaryOp(NullOp::SizeOf, _)
 319             | Rvalue::CheckedBinaryOp(..)
 320             | Rvalue::Cast(CastKind::Pointer(_), ..)
 321             | Rvalue::Discriminant(..)
 322             | Rvalue::Len(_)
 323             | Rvalue::Aggregate(..) => {}
 324
 325             Rvalue::Ref(_, kind @ BorrowKind::Mut { .. }, ref place)
 326             | Rvalue::Ref(_, kind @ BorrowKind::Unique, ref place) => {
 327                 let ty = place.ty(self.body, self.tcx).ty;
 328                 let is_allowed = match ty.kind {
 329                     // Inside a `static mut`, `&mut [...]` is allowed.
 330                     ty::Array(..) | ty::Slice(_) if self.const_kind() == ConstKind::StaticMut => {
 331                         true
 332                     }
 333
 334                     // FIXME(ecstaticmorse): We could allow `&mut []` inside a const context given
 335                     // that this is merely a ZST and it is already eligible for promotion.
 336                     // This may require an RFC?
 337                     /*
 338                     ty::Array(_, len) if len.try_eval_usize(cx.tcx, cx.param_env) == Some(0)
 339                         => true,
 340                     */
 341                     _ => false,
 342                 };
 343
 344                 if !is_allowed {
 345                     if let BorrowKind::Mut { .. } = kind {
 346                         self.check_op(ops::MutBorrow);
 347                     } else {
 348                         self.check_op(ops::CellBorrow);
 349                     }
 350                 }
 351             }
 352
 353             Rvalue::AddressOf(Mutability::Mut, _) => self.check_op(ops::MutAddressOf),
 354
 355             Rvalue::Ref(_, BorrowKind::Shared | BorrowKind::Shallow, ref place)
 356             | Rvalue::AddressOf(Mutability::Not, ref place) => {
 357                 let borrowed_place_has_mut_interior = qualifs::in_place::<HasMutInterior, _>(
 358                     &self.ccx,
 359                     &mut |local| self.qualifs.has_mut_interior(self.ccx, local, location),
 360                     place.as_ref(),
 361                 );
 362
 363                 if borrowed_place_has_mut_interior {
 364                     self.check_op(ops::CellBorrow);
 365                 }
 366             }
 367
 368             Rvalue::Cast(CastKind::Misc, ref operand, cast_ty) => {
 369                 let operand_ty = operand.ty(self.body, self.tcx);
 370                 let cast_in = CastTy::from_ty(operand_ty).expect("bad input type for cast");
 371                 let cast_out = CastTy::from_ty(cast_ty).expect("bad output type for cast");
 372
 373                 if let (CastTy::Ptr(_) | CastTy::FnPtr, CastTy::Int(_)) = (cast_in, cast_out) {
 374                     self.check_op(ops::RawPtrToIntCast);
 375                 }
 376             }
 377
 378             Rvalue::BinaryOp(op, ref lhs, _) => {
 379                 if let ty::RawPtr(_) | ty::FnPtr(..) = lhs.ty(self.body, self.tcx).kind {
 380                     assert!(
 381                         op == BinOp::Eq
 382                             || op == BinOp::Ne
 383                             || op == BinOp::Le
 384                             || op == BinOp::Lt
 385                             || op == BinOp::Ge
 386                             || op == BinOp::Gt
 387                             || op == BinOp::Offset
 388                     );
 389
 390                     self.check_op(ops::RawPtrComparison);
 391                 }
 392             }
 393
 394             Rvalue::NullaryOp(NullOp::Box, _) => {
 395                 self.check_op(ops::HeapAllocation);
 396             }
 397         }
 398     }
 399
 400     fn visit_operand(&mut self, op: &Operand<'tcx>, location: Location) {
 401         self.super_operand(op, location);
 402         if let Operand::Constant(c) = op {
 403             if let Some(def_id) = c.check_static_ptr(self.tcx) {
 404                 self.check_static(def_id, self.span);
 405             }
 406         }
 407     }
 408     fn visit_projection_elem(
 409         &mut self,
 410         place_local: Local,
 411         proj_base: &[PlaceElem<'tcx>],
 412         elem: &PlaceElem<'tcx>,
 413         context: PlaceContext,
 414         location: Location,
 415     ) {
 416         trace!(
 417             "visit_projection_elem: place_local={:?} proj_base={:?} elem={:?} \
 418             context={:?} location={:?}",
 419             place_local,
 420             proj_base,
 421             elem,
 422             context,
 423             location,
 424         );
 425
 426         self.super_projection_elem(place_local, proj_base, elem, context, location);
 427
 428         match elem {
 429             ProjectionElem::Deref => {
 430                 let base_ty = Place::ty_from(place_local, proj_base, self.body, self.tcx).ty;
 431                 if let ty::RawPtr(_) = base_ty.kind {
 432                     if proj_base.is_empty() {
 433                         if let (local, []) = (place_local, proj_base) {
 434                             let decl = &self.body.local_decls[local];
 435                             if let LocalInfo::StaticRef { def_id, .. } = decl.local_info {
 436                                 let span = decl.source_info.span;
 437                                 self.check_static(def_id, span);
 438                                 return;
 439                             }
 440                         }
 441                     }
 442                     self.check_op(ops::RawPtrDeref);
 443                 }
 444
 445                 if context.is_mutating_use() {
 446                     self.check_op(ops::MutDeref);
 447                 }
 448             }
 449
 450             ProjectionElem::ConstantIndex { .. }
 451             | ProjectionElem::Subslice { .. }
 452             | ProjectionElem::Field(..)
 453             | ProjectionElem::Index(_) => {
 454                 let base_ty = Place::ty_from(place_local, proj_base, self.body, self.tcx).ty;
 455                 match base_ty.ty_adt_def() {
 456                     Some(def) if def.is_union() => {
 457                         self.check_op(ops::UnionAccess);
 458                     }
 459
 460                     _ => {}
 461                 }
 462             }
 463
 464             ProjectionElem::Downcast(..) => {
 465                 self.check_op(ops::Downcast);
 466             }
 467         }
 468     }
 469
 470     fn visit_source_info(&mut self, source_info: &SourceInfo) {
 471         trace!("visit_source_info: source_info={:?}", source_info);
 472         self.span = source_info.span;
 473     }
 474
 475     fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) {
 476         trace!("visit_statement: statement={:?} location={:?}", statement, location);
 477
 478         match statement.kind {
 479             StatementKind::Assign(..) | StatementKind::SetDiscriminant { .. } => {
 480                 self.super_statement(statement, location);
 481             }
 482
 483             StatementKind::FakeRead(
 484                 FakeReadCause::ForMatchedPlace
 485                 | FakeReadCause::ForMatchGuard
 486                 | FakeReadCause::ForGuardBinding,
 487                 _,
 488             ) => {
 489                 self.super_statement(statement, location);
 490                 self.check_op(ops::IfOrMatch);
 491             }
 492             StatementKind::LlvmInlineAsm { .. } => {
 493                 self.super_statement(statement, location);
 494                 self.check_op(ops::InlineAsm);
 495             }
 496
 497             StatementKind::FakeRead(FakeReadCause::ForLet | FakeReadCause::ForIndex, _)
 498             | StatementKind::StorageLive(_)
 499             | StatementKind::StorageDead(_)
 500             | StatementKind::Retag { .. }
 501             | StatementKind::AscribeUserType(..)
 502             | StatementKind::Nop => {}
 503         }
 504     }
 505
 506     fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location) {
 507         trace!("visit_terminator: terminator={:?} location={:?}", terminator, location);
 508         self.super_terminator(terminator, location);
 509
 510         match &terminator.kind {
 511             TerminatorKind::Call { func, .. } => {
 512                 let fn_ty = func.ty(self.body, self.tcx);
 513
 514                 let (def_id, substs) = match fn_ty.kind {
 515                     ty::FnDef(def_id, substs) => (def_id, substs),
 516
 517                     ty::FnPtr(_) => {
 518                         self.check_op(ops::FnCallIndirect);
 519                         return;
 520                     }
 521                     _ => {
 522                         span_bug!(terminator.source_info.span, "invalid callee of type {:?}", fn_ty)
 523                     }
 524                 };
 525
 526                 // At this point, we are calling a function whose `DefId` is known...
 527                 if is_const_fn(self.tcx, def_id) {
 528                     return;
 529                 }
 530
 531                 // See if this is a trait method for a concrete type whose impl of that trait is
 532                 // `const`.
 533                 if self.tcx.features().const_trait_impl {
 534                     let instance = Instance::resolve(self.tcx, self.param_env, def_id, substs);
 535                     debug!("Resolving ({:?}) -> {:?}", def_id, instance);
 536                     if let Ok(Some(func)) = instance {
 537                         if let InstanceDef::Item(def_id) = func.def {
 538                             if is_const_fn(self.tcx, def_id) {
 539                                 return;
 540                             }
 541                         }
 542                     }
 543                 }
 544
 545                 if is_lang_panic_fn(self.tcx, def_id) {
 546                     self.check_op(ops::Panic);
 547                 } else if let Some(feature) = is_unstable_const_fn(self.tcx, def_id) {
 548                     // Exempt unstable const fns inside of macros with
 549                     // `#[allow_internal_unstable]`.
 550                     if !self.span.allows_unstable(feature) {
 551                         self.check_op(ops::FnCallUnstable(def_id, feature));
 552                     }
 553                 } else {
 554                     self.check_op(ops::FnCallNonConst(def_id));
 555                 }
 556             }
 557
 558             // Forbid all `Drop` terminators unless the place being dropped is a local with no
 559             // projections that cannot be `NeedsDrop`.
 560             TerminatorKind::Drop { location: dropped_place, .. }
 561             | TerminatorKind::DropAndReplace { location: dropped_place, .. } => {
 562                 let mut err_span = self.span;
 563
 564                 // Check to see if the type of this place can ever have a drop impl. If not, this
 565                 // `Drop` terminator is frivolous.
 566                 let ty_needs_drop =
 567                     dropped_place.ty(self.body, self.tcx).ty.needs_drop(self.tcx, self.param_env);
 568
 569                 if !ty_needs_drop {
 570                     return;
 571                 }
 572
 573                 let needs_drop = if let Some(local) = dropped_place.as_local() {
 574                     // Use the span where the local was declared as the span of the drop error.
 575                     err_span = self.body.local_decls[local].source_info.span;
 576                     self.qualifs.needs_drop(self.ccx, local, location)
 577                 } else {
 578                     true
 579                 };
 580
 581                 if needs_drop {
 582                     self.check_op_spanned(ops::LiveDrop, err_span);
 583                 }
 584             }
 585
 586             // FIXME: Some of these are only caught by `min_const_fn`, but should error here
 587             // instead.
 588             TerminatorKind::Abort
 589             | TerminatorKind::Assert { .. }
 590             | TerminatorKind::FalseEdges { .. }
 591             | TerminatorKind::FalseUnwind { .. }
 592             | TerminatorKind::GeneratorDrop
 593             | TerminatorKind::Goto { .. }
 594             | TerminatorKind::Resume
 595             | TerminatorKind::Return
 596             | TerminatorKind::SwitchInt { .. }
 597             | TerminatorKind::Unreachable
 598             | TerminatorKind::Yield { .. } => {}
 599         }
 600     }
 601 }
 602
 603 fn error_min_const_fn_violation(tcx: TyCtxt<'_>, span: Span, msg: Cow<'_, str>) {
 604     struct_span_err!(tcx.sess, span, E0723, "{}", msg)
 605         .note(
 606             "see issue #57563 <https://github.com/rust-lang/rust/issues/57563> \
 607              for more information",
 608         )
 609         .help("add `#![feature(const_fn)]` to the crate attributes to enable")
 610         .emit();
 611 }
 612
 613 fn check_short_circuiting_in_const_local(ccx: &ConstCx<'_, 'tcx>) {
 614     let body = ccx.body;
 615
 616     if body.control_flow_destroyed.is_empty() {
 617         return;
 618     }
 619
 620     let mut locals = body.vars_iter();
 621     if let Some(local) = locals.next() {
 622         let span = body.local_decls[local].source_info.span;
 623         let mut error = ccx.tcx.sess.struct_span_err(
 624             span,
 625             &format!(
 626                 "new features like let bindings are not permitted in {}s \
 627                 which also use short circuiting operators",
 628                 ccx.const_kind(),
 629             ),
 630         );
 631         for (span, kind) in body.control_flow_destroyed.iter() {
 632             error.span_note(
 633                 *span,
 634                 &format!(
 635                     "use of {} here does not actually short circuit due to \
 636                      the const evaluator presently not being able to do control flow. \
 637                      See issue #49146 <https://github.com/rust-lang/rust/issues/49146> \
 638                      for more information.",
 639                     kind
 640                 ),
 641             );
 642         }
 643         for local in locals {
 644             let span = body.local_decls[local].source_info.span;
 645             error.span_note(span, "more locals are defined here");
 646         }
 647         error.emit();
 648     }
 649 }
 650
 651 fn check_return_ty_is_sync(tcx: TyCtxt<'tcx>, body: &Body<'tcx>, hir_id: HirId) {
 652     let ty = body.return_ty();
 653     tcx.infer_ctxt().enter(|infcx| {
 654         let cause = traits::ObligationCause::new(body.span, hir_id, traits::SharedStatic);
 655         let mut fulfillment_cx = traits::FulfillmentContext::new();
 656         let sync_def_id = tcx.require_lang_item(lang_items::SyncTraitLangItem, Some(body.span));
 657         fulfillment_cx.register_bound(&infcx, ty::ParamEnv::empty(), ty, sync_def_id, cause);
 658         if let Err(err) = fulfillment_cx.select_all_or_error(&infcx) {
 659             infcx.report_fulfillment_errors(&err, None, false);
 660         }
 661     });
 662 }
 663
 664 fn place_as_reborrow(
 665     tcx: TyCtxt<'tcx>,
 666     body: &Body<'tcx>,
 667     place: Place<'tcx>,
 668 ) -> Option<&'a [PlaceElem<'tcx>]> {
 669     place.projection.split_last().and_then(|(outermost, inner)| {
 670         if outermost != &ProjectionElem::Deref {
 671             return None;
 672         }
 673
 674         // A borrow of a `static` also looks like `&(*_1)` in the MIR, but `_1` is a `const`
 675         // that points to the allocation for the static. Don't treat these as reborrows.
 676         if body.local_decls[place.local].is_ref_to_static() {
 677             return None;
 678         }
 679
 680         // Ensure the type being derefed is a reference and not a raw pointer.
 681         //
 682         // This is sufficient to prevent an access to a `static mut` from being marked as a
 683         // reborrow, even if the check above were to disappear.
 684         let inner_ty = Place::ty_from(place.local, inner, body, tcx).ty;
 685         match inner_ty.kind {
 686             ty::Ref(..) => Some(inner),
 687             _ => None,
 688         }
 689     })
 690 }