//! The `Visitor` responsible for actually checking a `mir::Body` for invalid operations. use rustc_errors::{Diagnostic, ErrorGuaranteed}; use rustc_hir as hir; use rustc_hir::def_id::DefId; use rustc_index::bit_set::BitSet; use rustc_infer::infer::TyCtxtInferExt; use rustc_infer::traits::{ImplSource, Obligation, ObligationCause}; use rustc_middle::mir::visit::{MutatingUseContext, NonMutatingUseContext, PlaceContext, Visitor}; use rustc_middle::mir::*; use rustc_middle::ty::subst::{GenericArgKind, InternalSubsts}; use rustc_middle::ty::{self, adjustment::PointerCast, Instance, InstanceDef, Ty, TyCtxt}; use rustc_middle::ty::{Binder, TraitRef, TypeVisitableExt}; use rustc_mir_dataflow::{self, Analysis}; use rustc_span::{sym, Span, Symbol}; use rustc_trait_selection::traits::error_reporting::TypeErrCtxtExt as _; use rustc_trait_selection::traits::{self, ObligationCauseCode, ObligationCtxt, SelectionContext}; use std::mem; use std::ops::Deref; use super::ops::{self, NonConstOp, Status}; use super::qualifs::{self, CustomEq, HasMutInterior, NeedsDrop, NeedsNonConstDrop}; use super::resolver::FlowSensitiveAnalysis; use super::{ConstCx, Qualif}; use crate::const_eval::is_unstable_const_fn; use crate::errors::UnstableInStable; type QualifResults<'mir, 'tcx, Q> = rustc_mir_dataflow::ResultsCursor<'mir, 'tcx, FlowSensitiveAnalysis<'mir, 'mir, 'tcx, Q>>; #[derive(Default)] pub struct Qualifs<'mir, 'tcx> { has_mut_interior: Option>, needs_drop: Option>, needs_non_const_drop: Option>, } impl<'mir, 'tcx> Qualifs<'mir, 'tcx> { /// Returns `true` if `local` is `NeedsDrop` at the given `Location`. /// /// Only updates the cursor if absolutely necessary pub fn needs_drop( &mut self, ccx: &'mir ConstCx<'mir, 'tcx>, local: Local, location: Location, ) -> bool { let ty = ccx.body.local_decls[local].ty; // Peeking into opaque types causes cycles if the current function declares said opaque // type. Thus we avoid short circuiting on the type and instead run the more expensive // analysis that looks at the actual usage within this function if !ty.has_opaque_types() && !NeedsDrop::in_any_value_of_ty(ccx, ty) { return false; } let needs_drop = self.needs_drop.get_or_insert_with(|| { let ConstCx { tcx, body, .. } = *ccx; FlowSensitiveAnalysis::new(NeedsDrop, ccx) .into_engine(tcx, &body) .iterate_to_fixpoint() .into_results_cursor(&body) }); needs_drop.seek_before_primary_effect(location); needs_drop.get().contains(local) } /// Returns `true` if `local` is `NeedsNonConstDrop` at the given `Location`. /// /// Only updates the cursor if absolutely necessary pub fn needs_non_const_drop( &mut self, ccx: &'mir ConstCx<'mir, 'tcx>, local: Local, location: Location, ) -> bool { let ty = ccx.body.local_decls[local].ty; if !NeedsNonConstDrop::in_any_value_of_ty(ccx, ty) { return false; } let needs_non_const_drop = self.needs_non_const_drop.get_or_insert_with(|| { let ConstCx { tcx, body, .. } = *ccx; FlowSensitiveAnalysis::new(NeedsNonConstDrop, ccx) .into_engine(tcx, &body) .iterate_to_fixpoint() .into_results_cursor(&body) }); needs_non_const_drop.seek_before_primary_effect(location); needs_non_const_drop.get().contains(local) } /// Returns `true` if `local` is `HasMutInterior` at the given `Location`. /// /// Only updates the cursor if absolutely necessary. pub fn has_mut_interior( &mut self, ccx: &'mir ConstCx<'mir, 'tcx>, local: Local, location: Location, ) -> bool { let ty = ccx.body.local_decls[local].ty; // Peeking into opaque types causes cycles if the current function declares said opaque // type. Thus we avoid short circuiting on the type and instead run the more expensive // analysis that looks at the actual usage within this function if !ty.has_opaque_types() && !HasMutInterior::in_any_value_of_ty(ccx, ty) { return false; } let has_mut_interior = self.has_mut_interior.get_or_insert_with(|| { let ConstCx { tcx, body, .. } = *ccx; FlowSensitiveAnalysis::new(HasMutInterior, ccx) .into_engine(tcx, &body) .iterate_to_fixpoint() .into_results_cursor(&body) }); has_mut_interior.seek_before_primary_effect(location); has_mut_interior.get().contains(local) } fn in_return_place( &mut self, ccx: &'mir ConstCx<'mir, 'tcx>, tainted_by_errors: Option, ) -> ConstQualifs { // Find the `Return` terminator if one exists. // // If no `Return` terminator exists, this MIR is divergent. Just return the conservative // qualifs for the return type. let return_block = ccx .body .basic_blocks .iter_enumerated() .find(|(_, block)| matches!(block.terminator().kind, TerminatorKind::Return)) .map(|(bb, _)| bb); let Some(return_block) = return_block else { return qualifs::in_any_value_of_ty(ccx, ccx.body.return_ty(), tainted_by_errors); }; let return_loc = ccx.body.terminator_loc(return_block); let custom_eq = match ccx.const_kind() { // We don't care whether a `const fn` returns a value that is not structurally // matchable. Functions calls are opaque and always use type-based qualification, so // this value should never be used. hir::ConstContext::ConstFn => true, // If we know that all values of the return type are structurally matchable, there's no // need to run dataflow. // Opaque types do not participate in const generics or pattern matching, so we can safely count them out. _ if ccx.body.return_ty().has_opaque_types() || !CustomEq::in_any_value_of_ty(ccx, ccx.body.return_ty()) => { false } hir::ConstContext::Const | hir::ConstContext::Static(_) => { let mut cursor = FlowSensitiveAnalysis::new(CustomEq, ccx) .into_engine(ccx.tcx, &ccx.body) .iterate_to_fixpoint() .into_results_cursor(&ccx.body); cursor.seek_after_primary_effect(return_loc); cursor.get().contains(RETURN_PLACE) } }; ConstQualifs { needs_drop: self.needs_drop(ccx, RETURN_PLACE, return_loc), needs_non_const_drop: self.needs_non_const_drop(ccx, RETURN_PLACE, return_loc), has_mut_interior: self.has_mut_interior(ccx, RETURN_PLACE, return_loc), custom_eq, tainted_by_errors, } } } pub struct Checker<'mir, 'tcx> { ccx: &'mir ConstCx<'mir, 'tcx>, qualifs: Qualifs<'mir, 'tcx>, /// The span of the current statement. span: Span, /// A set that stores for each local whether it has a `StorageDead` for it somewhere. local_has_storage_dead: Option>, error_emitted: Option, secondary_errors: Vec, } impl<'mir, 'tcx> Deref for Checker<'mir, 'tcx> { type Target = ConstCx<'mir, 'tcx>; fn deref(&self) -> &Self::Target { &self.ccx } } impl<'mir, 'tcx> Checker<'mir, 'tcx> { pub fn new(ccx: &'mir ConstCx<'mir, 'tcx>) -> Self { Checker { span: ccx.body.span, ccx, qualifs: Default::default(), local_has_storage_dead: None, error_emitted: None, secondary_errors: Vec::new(), } } pub fn check_body(&mut self) { let ConstCx { tcx, body, .. } = *self.ccx; let def_id = self.ccx.def_id(); // `async` functions cannot be `const fn`. This is checked during AST lowering, so there's // no need to emit duplicate errors here. if self.ccx.is_async() || body.generator.is_some() { tcx.sess.delay_span_bug(body.span, "`async` functions cannot be `const fn`"); return; } // The local type and predicate checks are not free and only relevant for `const fn`s. if self.const_kind() == hir::ConstContext::ConstFn { for (idx, local) in body.local_decls.iter_enumerated() { // Handle the return place below. if idx == RETURN_PLACE || local.internal { continue; } self.span = local.source_info.span; self.check_local_or_return_ty(local.ty, idx); } // impl trait is gone in MIR, so check the return type of a const fn by its signature // instead of the type of the return place. self.span = body.local_decls[RETURN_PLACE].source_info.span; let return_ty = self.ccx.fn_sig().output(); self.check_local_or_return_ty(return_ty.skip_binder(), RETURN_PLACE); } if !tcx.has_attr(def_id.to_def_id(), sym::rustc_do_not_const_check) { self.visit_body(&body); } // If we got through const-checking without emitting any "primary" errors, emit any // "secondary" errors if they occurred. let secondary_errors = mem::take(&mut self.secondary_errors); if self.error_emitted.is_none() { for mut error in secondary_errors { self.tcx.sess.diagnostic().emit_diagnostic(&mut error); } } else { assert!(self.tcx.sess.has_errors().is_some()); } } fn local_has_storage_dead(&mut self, local: Local) -> bool { let ccx = self.ccx; self.local_has_storage_dead .get_or_insert_with(|| { struct StorageDeads { locals: BitSet, } impl<'tcx> Visitor<'tcx> for StorageDeads { fn visit_statement(&mut self, stmt: &Statement<'tcx>, _: Location) { if let StatementKind::StorageDead(l) = stmt.kind { self.locals.insert(l); } } } let mut v = StorageDeads { locals: BitSet::new_empty(ccx.body.local_decls.len()) }; v.visit_body(ccx.body); v.locals }) .contains(local) } pub fn qualifs_in_return_place(&mut self) -> ConstQualifs { self.qualifs.in_return_place(self.ccx, self.error_emitted) } /// Emits an error if an expression cannot be evaluated in the current context. pub fn check_op(&mut self, op: impl NonConstOp<'tcx>) { self.check_op_spanned(op, self.span); } /// Emits an error at the given `span` if an expression cannot be evaluated in the current /// context. pub fn check_op_spanned>(&mut self, op: O, span: Span) { let gate = match op.status_in_item(self.ccx) { Status::Allowed => return, Status::Unstable(gate) if self.tcx.features().enabled(gate) => { let unstable_in_stable = self.ccx.is_const_stable_const_fn() && !super::rustc_allow_const_fn_unstable(self.tcx, self.def_id(), gate); if unstable_in_stable { emit_unstable_in_stable_error(self.ccx, span, gate); } return; } Status::Unstable(gate) => Some(gate), Status::Forbidden => None, }; if self.tcx.sess.opts.unstable_opts.unleash_the_miri_inside_of_you { self.tcx.sess.miri_unleashed_feature(span, gate); return; } let mut err = op.build_error(self.ccx, span); assert!(err.is_error()); match op.importance() { ops::DiagnosticImportance::Primary => { let reported = err.emit(); self.error_emitted = Some(reported); } ops::DiagnosticImportance::Secondary => err.buffer(&mut self.secondary_errors), } } fn check_static(&mut self, def_id: DefId, span: Span) { if self.tcx.is_thread_local_static(def_id) { self.tcx.sess.delay_span_bug(span, "tls access is checked in `Rvalue::ThreadLocalRef`"); } self.check_op_spanned(ops::StaticAccess, span) } fn check_local_or_return_ty(&mut self, ty: Ty<'tcx>, local: Local) { let kind = self.body.local_kind(local); for ty in ty.walk() { let ty = match ty.unpack() { GenericArgKind::Type(ty) => ty, // No constraints on lifetimes or constants, except potentially // constants' types, but `walk` will get to them as well. GenericArgKind::Lifetime(_) | GenericArgKind::Const(_) => continue, }; match *ty.kind() { ty::Ref(_, _, hir::Mutability::Mut) => self.check_op(ops::ty::MutRef(kind)), _ => {} } } } fn check_mut_borrow(&mut self, local: Local, kind: hir::BorrowKind) { match self.const_kind() { // In a const fn all borrows are transient or point to the places given via // references in the arguments (so we already checked them with // TransientMutBorrow/MutBorrow as appropriate). // The borrow checker guarantees that no new non-transient borrows are created. // NOTE: Once we have heap allocations during CTFE we need to figure out // how to prevent `const fn` to create long-lived allocations that point // to mutable memory. hir::ConstContext::ConstFn => self.check_op(ops::TransientMutBorrow(kind)), _ => { // Locals with StorageDead do not live beyond the evaluation and can // thus safely be borrowed without being able to be leaked to the final // value of the constant. if self.local_has_storage_dead(local) { self.check_op(ops::TransientMutBorrow(kind)); } else { self.check_op(ops::MutBorrow(kind)); } } } } } impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> { fn visit_basic_block_data(&mut self, bb: BasicBlock, block: &BasicBlockData<'tcx>) { trace!("visit_basic_block_data: bb={:?} is_cleanup={:?}", bb, block.is_cleanup); // We don't const-check basic blocks on the cleanup path since we never unwind during // const-eval: a panic causes an immediate compile error. In other words, cleanup blocks // are unreachable during const-eval. // // We can't be more conservative (e.g., by const-checking cleanup blocks anyways) because // locals that would never be dropped during normal execution are sometimes dropped during // unwinding, which means backwards-incompatible live-drop errors. if block.is_cleanup { return; } self.super_basic_block_data(bb, block); } fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, location: Location) { trace!("visit_rvalue: rvalue={:?} location={:?}", rvalue, location); // Special-case reborrows to be more like a copy of a reference. match *rvalue { Rvalue::Ref(_, kind, place) => { if let Some(reborrowed_place_ref) = place_as_reborrow(self.tcx, self.body, place) { let ctx = match kind { BorrowKind::Shared => { PlaceContext::NonMutatingUse(NonMutatingUseContext::SharedBorrow) } BorrowKind::Shallow => { PlaceContext::NonMutatingUse(NonMutatingUseContext::ShallowBorrow) } BorrowKind::Unique => { PlaceContext::NonMutatingUse(NonMutatingUseContext::UniqueBorrow) } BorrowKind::Mut { .. } => { PlaceContext::MutatingUse(MutatingUseContext::Borrow) } }; self.visit_local(reborrowed_place_ref.local, ctx, location); self.visit_projection(reborrowed_place_ref, ctx, location); return; } } Rvalue::AddressOf(mutbl, place) => { if let Some(reborrowed_place_ref) = place_as_reborrow(self.tcx, self.body, place) { let ctx = match mutbl { Mutability::Not => { PlaceContext::NonMutatingUse(NonMutatingUseContext::AddressOf) } Mutability::Mut => PlaceContext::MutatingUse(MutatingUseContext::AddressOf), }; self.visit_local(reborrowed_place_ref.local, ctx, location); self.visit_projection(reborrowed_place_ref, ctx, location); return; } } _ => {} } self.super_rvalue(rvalue, location); match rvalue { Rvalue::ThreadLocalRef(_) => self.check_op(ops::ThreadLocalAccess), Rvalue::Use(_) | Rvalue::CopyForDeref(..) | Rvalue::Repeat(..) | Rvalue::Discriminant(..) | Rvalue::Len(_) => {} Rvalue::Aggregate(kind, ..) => { if let AggregateKind::Generator(def_id, ..) = kind.as_ref() && let Some(generator_kind @ hir::GeneratorKind::Async(..)) = self.tcx.generator_kind(def_id) { self.check_op(ops::Generator(generator_kind)); } } Rvalue::Ref(_, kind @ (BorrowKind::Mut { .. } | BorrowKind::Unique), place) => { let ty = place.ty(self.body, self.tcx).ty; let is_allowed = match ty.kind() { // Inside a `static mut`, `&mut [...]` is allowed. ty::Array(..) | ty::Slice(_) if self.const_kind() == hir::ConstContext::Static(hir::Mutability::Mut) => { true } // FIXME(ecstaticmorse): We could allow `&mut []` inside a const context given // that this is merely a ZST and it is already eligible for promotion. // This may require an RFC? /* ty::Array(_, len) if len.try_eval_target_usize(cx.tcx, cx.param_env) == Some(0) => true, */ _ => false, }; if !is_allowed { if let BorrowKind::Mut { .. } = kind { self.check_mut_borrow(place.local, hir::BorrowKind::Ref) } else { self.check_op(ops::CellBorrow); } } } Rvalue::AddressOf(Mutability::Mut, place) => { self.check_mut_borrow(place.local, hir::BorrowKind::Raw) } Rvalue::Ref(_, BorrowKind::Shared | BorrowKind::Shallow, place) | Rvalue::AddressOf(Mutability::Not, place) => { let borrowed_place_has_mut_interior = qualifs::in_place::( &self.ccx, &mut |local| self.qualifs.has_mut_interior(self.ccx, local, location), place.as_ref(), ); if borrowed_place_has_mut_interior { match self.const_kind() { // In a const fn all borrows are transient or point to the places given via // references in the arguments (so we already checked them with // TransientCellBorrow/CellBorrow as appropriate). // The borrow checker guarantees that no new non-transient borrows are created. // NOTE: Once we have heap allocations during CTFE we need to figure out // how to prevent `const fn` to create long-lived allocations that point // to (interior) mutable memory. hir::ConstContext::ConstFn => self.check_op(ops::TransientCellBorrow), _ => { // Locals with StorageDead are definitely not part of the final constant value, and // it is thus inherently safe to permit such locals to have their // address taken as we can't end up with a reference to them in the // final value. // Note: This is only sound if every local that has a `StorageDead` has a // `StorageDead` in every control flow path leading to a `return` terminator. if self.local_has_storage_dead(place.local) { self.check_op(ops::TransientCellBorrow); } else { self.check_op(ops::CellBorrow); } } } } } Rvalue::Cast( CastKind::Pointer( PointerCast::MutToConstPointer | PointerCast::ArrayToPointer | PointerCast::UnsafeFnPointer | PointerCast::ClosureFnPointer(_) | PointerCast::ReifyFnPointer, ), _, _, ) => { // These are all okay; they only change the type, not the data. } Rvalue::Cast(CastKind::Pointer(PointerCast::Unsize), _, _) => { // Unsizing is implemented for CTFE. } Rvalue::Cast(CastKind::PointerExposeAddress, _, _) => { self.check_op(ops::RawPtrToIntCast); } Rvalue::Cast(CastKind::PointerFromExposedAddress, _, _) => { // Since no pointer can ever get exposed (rejected above), this is easy to support. } Rvalue::Cast(CastKind::DynStar, _, _) => { unimplemented!() } Rvalue::Cast(_, _, _) => {} Rvalue::NullaryOp(NullOp::SizeOf | NullOp::AlignOf, _) => {} Rvalue::ShallowInitBox(_, _) => {} Rvalue::UnaryOp(_, operand) => { let ty = operand.ty(self.body, self.tcx); if is_int_bool_or_char(ty) { // Int, bool, and char operations are fine. } else if ty.is_floating_point() { self.check_op(ops::FloatingPointOp); } else { span_bug!(self.span, "non-primitive type in `Rvalue::UnaryOp`: {:?}", ty); } } Rvalue::BinaryOp(op, box (lhs, rhs)) | Rvalue::CheckedBinaryOp(op, box (lhs, rhs)) => { let lhs_ty = lhs.ty(self.body, self.tcx); let rhs_ty = rhs.ty(self.body, self.tcx); if is_int_bool_or_char(lhs_ty) && is_int_bool_or_char(rhs_ty) { // Int, bool, and char operations are fine. } else if lhs_ty.is_fn_ptr() || lhs_ty.is_unsafe_ptr() { assert_eq!(lhs_ty, rhs_ty); assert!( matches!( op, BinOp::Eq | BinOp::Ne | BinOp::Le | BinOp::Lt | BinOp::Ge | BinOp::Gt | BinOp::Offset ) ); self.check_op(ops::RawPtrComparison); } else if lhs_ty.is_floating_point() || rhs_ty.is_floating_point() { self.check_op(ops::FloatingPointOp); } else { span_bug!( self.span, "non-primitive type in `Rvalue::BinaryOp`: {:?} ⚬ {:?}", lhs_ty, rhs_ty ); } } } } fn visit_operand(&mut self, op: &Operand<'tcx>, location: Location) { self.super_operand(op, location); if let Operand::Constant(c) = op { if let Some(def_id) = c.check_static_ptr(self.tcx) { self.check_static(def_id, self.span); } } } fn visit_projection_elem( &mut self, place_local: Local, proj_base: &[PlaceElem<'tcx>], elem: PlaceElem<'tcx>, context: PlaceContext, location: Location, ) { trace!( "visit_projection_elem: place_local={:?} proj_base={:?} elem={:?} \ context={:?} location={:?}", place_local, proj_base, elem, context, location, ); self.super_projection_elem(place_local, proj_base, elem, context, location); match elem { ProjectionElem::Deref => { let base_ty = Place::ty_from(place_local, proj_base, self.body, self.tcx).ty; if base_ty.is_unsafe_ptr() { if proj_base.is_empty() { let decl = &self.body.local_decls[place_local]; if let Some(box LocalInfo::StaticRef { def_id, .. }) = decl.local_info { let span = decl.source_info.span; self.check_static(def_id, span); return; } } // `*const T` is stable, `*mut T` is not if !base_ty.is_mutable_ptr() { return; } self.check_op(ops::RawMutPtrDeref); } if context.is_mutating_use() { self.check_op(ops::MutDeref); } } ProjectionElem::ConstantIndex { .. } | ProjectionElem::Downcast(..) | ProjectionElem::OpaqueCast(..) | ProjectionElem::Subslice { .. } | ProjectionElem::Field(..) | ProjectionElem::Index(_) => {} } } fn visit_source_info(&mut self, source_info: &SourceInfo) { trace!("visit_source_info: source_info={:?}", source_info); self.span = source_info.span; } fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) { trace!("visit_statement: statement={:?} location={:?}", statement, location); self.super_statement(statement, location); match statement.kind { StatementKind::Assign(..) | StatementKind::SetDiscriminant { .. } | StatementKind::Deinit(..) | StatementKind::FakeRead(..) | StatementKind::StorageLive(_) | StatementKind::StorageDead(_) | StatementKind::Retag { .. } | StatementKind::AscribeUserType(..) | StatementKind::Coverage(..) | StatementKind::Intrinsic(..) | StatementKind::ConstEvalCounter | StatementKind::Nop => {} } } #[instrument(level = "debug", skip(self))] fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location) { self.super_terminator(terminator, location); match &terminator.kind { TerminatorKind::Call { func, args, fn_span, from_hir_call, .. } => { let ConstCx { tcx, body, param_env, .. } = *self.ccx; let caller = self.def_id(); let fn_ty = func.ty(body, tcx); let (mut callee, mut substs) = match *fn_ty.kind() { ty::FnDef(def_id, substs) => (def_id, substs), ty::FnPtr(_) => { self.check_op(ops::FnCallIndirect); return; } _ => { span_bug!(terminator.source_info.span, "invalid callee of type {:?}", fn_ty) } }; // Attempting to call a trait method? if let Some(trait_id) = tcx.trait_of_item(callee) { trace!("attempting to call a trait method"); if !self.tcx.features().const_trait_impl { self.check_op(ops::FnCallNonConst { caller, callee, substs, span: *fn_span, from_hir_call: *from_hir_call, feature: Some(sym::const_trait_impl), }); return; } let trait_ref = TraitRef::from_method(tcx, trait_id, substs); let poly_trait_pred = Binder::dummy(trait_ref).with_constness(ty::BoundConstness::ConstIfConst); let obligation = Obligation::new(tcx, ObligationCause::dummy(), param_env, poly_trait_pred); let implsrc = { let infcx = tcx.infer_ctxt().build(); let mut selcx = SelectionContext::new(&infcx); selcx.select(&obligation) }; // do a well-formedness check on the trait method being called. This is because typeck only does a // "non-const" check. This is required for correctness here. { let infcx = tcx.infer_ctxt().build(); let ocx = ObligationCtxt::new(&infcx); let predicates = tcx.predicates_of(callee).instantiate(tcx, substs); let cause = ObligationCause::new( terminator.source_info.span, self.body.source.def_id().expect_local(), ObligationCauseCode::ItemObligation(callee), ); let normalized_predicates = ocx.normalize(&cause, param_env, predicates); ocx.register_obligations(traits::predicates_for_generics( |_, _| cause.clone(), self.param_env, normalized_predicates, )); let errors = ocx.select_all_or_error(); if !errors.is_empty() { infcx.err_ctxt().report_fulfillment_errors(&errors, None); } } match implsrc { Ok(Some(ImplSource::Param(_, ty::BoundConstness::ConstIfConst))) => { debug!( "const_trait_impl: provided {:?} via where-clause in {:?}", trait_ref, param_env ); return; } Ok(Some(ImplSource::Closure(data))) => { if !tcx.is_const_fn_raw(data.closure_def_id) { self.check_op(ops::FnCallNonConst { caller, callee, substs, span: *fn_span, from_hir_call: *from_hir_call, feature: None, }); return; } } Ok(Some(ImplSource::UserDefined(data))) => { let callee_name = tcx.item_name(callee); if let Some(&did) = tcx .associated_item_def_ids(data.impl_def_id) .iter() .find(|did| tcx.item_name(**did) == callee_name) { // using internal substs is ok here, since this is only // used for the `resolve` call below substs = InternalSubsts::identity_for_item(tcx, did); callee = did; } if let hir::Constness::NotConst = tcx.constness(data.impl_def_id) { self.check_op(ops::FnCallNonConst { caller, callee, substs, span: *fn_span, from_hir_call: *from_hir_call, feature: None, }); return; } } _ if !tcx.is_const_fn_raw(callee) => { // At this point, it is only legal when the caller is in a trait // marked with #[const_trait], and the callee is in the same trait. let mut nonconst_call_permission = false; if let Some(callee_trait) = tcx.trait_of_item(callee) && tcx.has_attr(callee_trait, sym::const_trait) && Some(callee_trait) == tcx.trait_of_item(caller.to_def_id()) // Can only call methods when it's `::f`. && tcx.types.self_param == substs.type_at(0) { nonconst_call_permission = true; } if !nonconst_call_permission { let obligation = Obligation::new( tcx, ObligationCause::dummy_with_span(*fn_span), param_env, poly_trait_pred, ); // improve diagnostics by showing what failed. Our requirements are stricter this time // as we are going to error again anyways. let infcx = tcx.infer_ctxt().build(); if let Err(e) = implsrc { infcx.err_ctxt().report_selection_error( obligation.clone(), &obligation, &e, ); } self.check_op(ops::FnCallNonConst { caller, callee, substs, span: *fn_span, from_hir_call: *from_hir_call, feature: None, }); return; } } _ => {} } // Resolve a trait method call to its concrete implementation, which may be in a // `const` trait impl. let instance = Instance::resolve(tcx, param_env, callee, substs); debug!("Resolving ({:?}) -> {:?}", callee, instance); if let Ok(Some(func)) = instance { if let InstanceDef::Item(def) = func.def { callee = def.did; } } } // At this point, we are calling a function, `callee`, whose `DefId` is known... // `begin_panic` and `panic_display` are generic functions that accept // types other than str. Check to enforce that only str can be used in // const-eval. // const-eval of the `begin_panic` fn assumes the argument is `&str` if Some(callee) == tcx.lang_items().begin_panic_fn() { match args[0].ty(&self.ccx.body.local_decls, tcx).kind() { ty::Ref(_, ty, _) if ty.is_str() => return, _ => self.check_op(ops::PanicNonStr), } } // const-eval of the `panic_display` fn assumes the argument is `&&str` if Some(callee) == tcx.lang_items().panic_display() { match args[0].ty(&self.ccx.body.local_decls, tcx).kind() { ty::Ref(_, ty, _) if matches!(ty.kind(), ty::Ref(_, ty, _) if ty.is_str()) => { return; } _ => self.check_op(ops::PanicNonStr), } } if Some(callee) == tcx.lang_items().exchange_malloc_fn() { self.check_op(ops::HeapAllocation); return; } if !tcx.is_const_fn_raw(callee) { if !tcx.is_const_default_method(callee) { // To get to here we must have already found a const impl for the // trait, but for it to still be non-const can be that the impl is // using default method bodies. self.check_op(ops::FnCallNonConst { caller, callee, substs, span: *fn_span, from_hir_call: *from_hir_call, feature: None, }); return; } } // If the `const fn` we are trying to call is not const-stable, ensure that we have // the proper feature gate enabled. if let Some(gate) = is_unstable_const_fn(tcx, callee) { trace!(?gate, "calling unstable const fn"); if self.span.allows_unstable(gate) { return; } // Calling an unstable function *always* requires that the corresponding gate // be enabled, even if the function has `#[rustc_allow_const_fn_unstable(the_gate)]`. if !tcx.features().declared_lib_features.iter().any(|&(sym, _)| sym == gate) { self.check_op(ops::FnCallUnstable(callee, Some(gate))); return; } // If this crate is not using stability attributes, or the caller is not claiming to be a // stable `const fn`, that is all that is required. if !self.ccx.is_const_stable_const_fn() { trace!("crate not using stability attributes or caller not stably const"); return; } // Otherwise, we are something const-stable calling a const-unstable fn. if super::rustc_allow_const_fn_unstable(tcx, caller, gate) { trace!("rustc_allow_const_fn_unstable gate active"); return; } self.check_op(ops::FnCallUnstable(callee, Some(gate))); return; } // FIXME(ecstaticmorse); For compatibility, we consider `unstable` callees that // have no `rustc_const_stable` attributes to be const-unstable as well. This // should be fixed later. let callee_is_unstable_unmarked = tcx.lookup_const_stability(callee).is_none() && tcx.lookup_stability(callee).map_or(false, |s| s.is_unstable()); if callee_is_unstable_unmarked { trace!("callee_is_unstable_unmarked"); // We do not use `const` modifiers for intrinsic "functions", as intrinsics are // `extern` functions, and these have no way to get marked `const`. So instead we // use `rustc_const_(un)stable` attributes to mean that the intrinsic is `const` if self.ccx.is_const_stable_const_fn() || tcx.is_intrinsic(callee) { self.check_op(ops::FnCallUnstable(callee, None)); return; } } trace!("permitting call"); } // Forbid all `Drop` terminators unless the place being dropped is a local with no // projections that cannot be `NeedsNonConstDrop`. TerminatorKind::Drop { place: dropped_place, .. } | TerminatorKind::DropAndReplace { place: dropped_place, .. } => { // If we are checking live drops after drop-elaboration, don't emit duplicate // errors here. if super::post_drop_elaboration::checking_enabled(self.ccx) { return; } let mut err_span = self.span; let ty_of_dropped_place = dropped_place.ty(self.body, self.tcx).ty; let ty_needs_non_const_drop = qualifs::NeedsNonConstDrop::in_any_value_of_ty(self.ccx, ty_of_dropped_place); debug!(?ty_of_dropped_place, ?ty_needs_non_const_drop); if !ty_needs_non_const_drop { return; } let needs_non_const_drop = if let Some(local) = dropped_place.as_local() { // Use the span where the local was declared as the span of the drop error. err_span = self.body.local_decls[local].source_info.span; self.qualifs.needs_non_const_drop(self.ccx, local, location) } else { true }; if needs_non_const_drop { self.check_op_spanned( ops::LiveDrop { dropped_at: Some(terminator.source_info.span), dropped_ty: ty_of_dropped_place, }, err_span, ); } } TerminatorKind::InlineAsm { .. } => self.check_op(ops::InlineAsm), TerminatorKind::GeneratorDrop | TerminatorKind::Yield { .. } => { self.check_op(ops::Generator(hir::GeneratorKind::Gen)) } TerminatorKind::Abort => { // Cleanup blocks are skipped for const checking (see `visit_basic_block_data`). span_bug!(self.span, "`Abort` terminator outside of cleanup block") } TerminatorKind::Assert { .. } | TerminatorKind::FalseEdge { .. } | TerminatorKind::FalseUnwind { .. } | TerminatorKind::Goto { .. } | TerminatorKind::Resume | TerminatorKind::Return | TerminatorKind::SwitchInt { .. } | TerminatorKind::Unreachable => {} } } } fn place_as_reborrow<'tcx>( tcx: TyCtxt<'tcx>, body: &Body<'tcx>, place: Place<'tcx>, ) -> Option> { match place.as_ref().last_projection() { Some((place_base, ProjectionElem::Deref)) => { // A borrow of a `static` also looks like `&(*_1)` in the MIR, but `_1` is a `const` // that points to the allocation for the static. Don't treat these as reborrows. if body.local_decls[place_base.local].is_ref_to_static() { None } else { // Ensure the type being derefed is a reference and not a raw pointer. // This is sufficient to prevent an access to a `static mut` from being marked as a // reborrow, even if the check above were to disappear. let inner_ty = place_base.ty(body, tcx).ty; if let ty::Ref(..) = inner_ty.kind() { return Some(place_base); } else { return None; } } } _ => None, } } fn is_int_bool_or_char(ty: Ty<'_>) -> bool { ty.is_bool() || ty.is_integral() || ty.is_char() } fn emit_unstable_in_stable_error(ccx: &ConstCx<'_, '_>, span: Span, gate: Symbol) { let attr_span = ccx.tcx.def_span(ccx.def_id()).shrink_to_lo(); ccx.tcx.sess.emit_err(UnstableInStable { gate: gate.to_string(), span, attr_span }); }