diff options
Diffstat (limited to 'compiler/rustc_const_eval/src/transform/check_consts/check.rs')
| -rw-r--r-- | compiler/rustc_const_eval/src/transform/check_consts/check.rs | 1032 |
1 files changed, 1032 insertions, 0 deletions
diff --git a/compiler/rustc_const_eval/src/transform/check_consts/check.rs b/compiler/rustc_const_eval/src/transform/check_consts/check.rs new file mode 100644 index 000000000..0adb88a18 --- /dev/null +++ b/compiler/rustc_const_eval/src/transform/check_consts/check.rs @@ -0,0 +1,1032 @@ +//! 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, TraitPredicate, TraitRef, TypeVisitable}; +use rustc_mir_dataflow::{self, Analysis}; +use rustc_span::{sym, Span, Symbol}; +use rustc_trait_selection::traits::error_reporting::InferCtxtExt; +use rustc_trait_selection::traits::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<QualifResults<'mir, 'tcx, HasMutInterior>>, + needs_drop: Option<QualifResults<'mir, 'tcx, NeedsDrop>>, + needs_non_const_drop: Option<QualifResults<'mir, 'tcx, NeedsNonConstDrop>>, +} + +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<ErrorGuaranteed>, + ) -> 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<BitSet<Local>>, + + error_emitted: Option<ErrorGuaranteed>, + secondary_errors: Vec<Diagnostic>, +} + +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 = tcx.fn_sig(def_id).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<Local>, + } + 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<O: NonConstOp<'tcx>>(&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(..) => {} + + Rvalue::Ref(_, kind @ BorrowKind::Mut { .. }, ref place) + | Rvalue::Ref(_, kind @ BorrowKind::Unique, ref 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_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, ref place) => { + self.check_mut_borrow(place.local, hir::BorrowKind::Raw) + } + + Rvalue::Ref(_, BorrowKind::Shared | BorrowKind::Shallow, ref place) + | Rvalue::AddressOf(Mutability::Not, ref place) => { + let borrowed_place_has_mut_interior = qualifs::in_place::<HasMutInterior, _>( + &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::Misc, _, _) => {} + + Rvalue::NullaryOp(NullOp::SizeOf | NullOp::AlignOf, _) => {} + Rvalue::ShallowInitBox(_, _) => {} + + Rvalue::UnaryOp(_, ref 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 (ref lhs, ref rhs)) + | Rvalue::CheckedBinaryOp(op, box (ref lhs, ref 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!( + op == BinOp::Eq + || op == BinOp::Ne + || op == BinOp::Le + || op == BinOp::Lt + || op == BinOp::Ge + || op == BinOp::Gt + || op == 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::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::CopyNonOverlapping(..) + | 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, + }); + return; + } + + let trait_ref = TraitRef::from_method(tcx, trait_id, substs); + let poly_trait_pred = Binder::dummy(TraitPredicate { + trait_ref, + constness: ty::BoundConstness::ConstIfConst, + polarity: ty::ImplPolarity::Positive, + }); + let obligation = + Obligation::new(ObligationCause::dummy(), param_env, poly_trait_pred); + + let implsrc = tcx.infer_ctxt().enter(|infcx| { + let mut selcx = SelectionContext::new(&infcx); + selcx.select(&obligation) + }); + + 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::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, + }); + 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 `<Self as TheTrait>::f`. + && tcx.types.self_param == substs.type_at(0) + { + nonconst_call_permission = true; + } + + if !nonconst_call_permission { + let obligation = Obligation::new( + ObligationCause::dummy_with_span(*fn_span), + param_env, + tcx.mk_predicate( + poly_trait_pred.map_bound(ty::PredicateKind::Trait), + ), + ); + + // improve diagnostics by showing what failed. Our requirements are stricter this time + // as we are going to error again anyways. + tcx.infer_ctxt().enter(|infcx| { + if let Err(e) = implsrc { + infcx.report_selection_error( + obligation.clone(), + &obligation, + &e, + false, + ); + } + }); + + self.check_op(ops::FnCallNonConst { + caller, + callee, + substs, + span: *fn_span, + from_hir_call: *from_hir_call, + }); + 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; + } + + // `async` blocks get lowered to `std::future::from_generator(/* a closure */)`. + let is_async_block = Some(callee) == tcx.lang_items().from_generator_fn(); + if is_async_block { + let kind = hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Block); + self.check_op(ops::Generator(kind)); + return; + } + + let is_intrinsic = tcx.is_intrinsic(callee); + + 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, + }); + 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() || is_intrinsic { + 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) }, + 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<PlaceRef<'tcx>> { + 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 }); +} |