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//! The `Visitor` responsible for actually checking a `mir::Body` for invalid operations.
use std::assert_matches::assert_matches;
use std::borrow::Cow;
use std::mem;
use std::ops::Deref;
use rustc_errors::{Diag, ErrorGuaranteed};
use rustc_hir::def_id::DefId;
use rustc_hir::{self as hir, LangItem};
use rustc_index::bit_set::BitSet;
use rustc_infer::infer::TyCtxtInferExt;
use rustc_infer::traits::ObligationCause;
use rustc_middle::mir::visit::{MutatingUseContext, NonMutatingUseContext, PlaceContext, Visitor};
use rustc_middle::mir::*;
use rustc_middle::span_bug;
use rustc_middle::ty::adjustment::PointerCoercion;
use rustc_middle::ty::{self, Instance, InstanceKind, Ty, TyCtxt, TypeVisitableExt};
use rustc_mir_dataflow::impls::MaybeStorageLive;
use rustc_mir_dataflow::storage::always_storage_live_locals;
use rustc_mir_dataflow::Analysis;
use rustc_span::{sym, Span, Symbol, DUMMY_SP};
use rustc_trait_selection::error_reporting::InferCtxtErrorExt;
use rustc_trait_selection::traits::{self, ObligationCauseCode, ObligationCtxt};
use rustc_type_ir::visit::{TypeSuperVisitable, TypeVisitor};
use tracing::{debug, instrument, trace};
use super::ops::{self, NonConstOp, Status};
use super::qualifs::{self, 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(crate) 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;
// 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() && !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 {
// FIXME(explicit_tail_calls): uhhhh I think we can return without return now, does it change anything
// 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);
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),
tainted_by_errors,
}
}
}
struct LocalReturnTyVisitor<'ck, 'mir, 'tcx> {
kind: LocalKind,
checker: &'ck mut Checker<'mir, 'tcx>,
}
impl<'ck, 'mir, 'tcx> TypeVisitor<TyCtxt<'tcx>> for LocalReturnTyVisitor<'ck, 'mir, 'tcx> {
fn visit_ty(&mut self, t: Ty<'tcx>) {
match t.kind() {
ty::FnPtr(..) => {}
ty::Ref(_, _, hir::Mutability::Mut) => {
self.checker.check_op(ops::mut_ref::MutRef(self.kind));
t.super_visit_with(self)
}
_ => t.super_visit_with(self),
}
}
}
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 is "transient", i.e. guaranteed to be dead
/// when this MIR body returns.
transient_locals: Option<BitSet<Local>>,
error_emitted: Option<ErrorGuaranteed>,
secondary_errors: Vec<Diag<'tcx>>,
}
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(),
transient_locals: 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.coroutine.is_some() {
tcx.dcx().span_delayed_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 {
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, 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. Otherwise, cancel the "secondary" errors.
let secondary_errors = mem::take(&mut self.secondary_errors);
if self.error_emitted.is_none() {
for error in secondary_errors {
self.error_emitted = Some(error.emit());
}
} else {
assert!(self.tcx.dcx().has_errors().is_some());
for error in secondary_errors {
error.cancel();
}
}
}
fn local_is_transient(&mut self, local: Local) -> bool {
let ccx = self.ccx;
self.transient_locals
.get_or_insert_with(|| {
// A local is "transient" if it is guaranteed dead at all `Return`.
// So first compute the say of "maybe live" locals at each program point.
let always_live_locals = &always_storage_live_locals(&ccx.body);
let mut maybe_storage_live =
MaybeStorageLive::new(Cow::Borrowed(always_live_locals))
.into_engine(ccx.tcx, &ccx.body)
.iterate_to_fixpoint()
.into_results_cursor(&ccx.body);
// And then check all `Return` in the MIR, and if a local is "maybe live" at a
// `Return` then it is definitely not transient.
let mut transient = BitSet::new_filled(ccx.body.local_decls.len());
// Make sure to only visit reachable blocks, the dataflow engine can ICE otherwise.
for (bb, data) in traversal::reachable(&ccx.body) {
if matches!(data.terminator().kind, TerminatorKind::Return) {
let location = ccx.body.terminator_loc(bb);
maybe_storage_live.seek_after_primary_effect(location);
// If a local may be live here, it is definitely not transient.
transient.subtract(maybe_storage_live.get());
}
}
transient
})
.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().active(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 err = op.build_error(self.ccx, span);
assert!(err.is_error());
match op.importance() {
ops::DiagImportance::Primary => {
let reported = err.emit();
self.error_emitted = Some(reported);
}
ops::DiagImportance::Secondary => self.secondary_errors.push(err),
}
}
fn check_static(&mut self, def_id: DefId, span: Span) {
if self.tcx.is_thread_local_static(def_id) {
self.tcx.dcx().span_bug(span, "tls access is checked in `Rvalue::ThreadLocalRef`");
}
if let Some(def_id) = def_id.as_local()
&& let Err(guar) = self.tcx.at(span).check_well_formed(hir::OwnerId { def_id })
{
self.error_emitted = Some(guar);
}
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);
let mut visitor = LocalReturnTyVisitor { kind, checker: self };
visitor.visit_ty(ty);
}
fn check_mut_borrow(&mut self, place: &Place<'_>, 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)),
_ => {
// For indirect places, we are not creating a new permanent borrow, it's just as
// transient as the already existing one. For reborrowing references this is handled
// at the top of `visit_rvalue`, but for raw pointers we handle it here.
// Pointers/references to `static mut` and cases where the `*` is not the first
// projection also end up here.
// 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.
// 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.
// The good news is that interning will detect if any unexpected mutable
// pointer slips through.
if place.is_indirect() || self.local_is_transient(place.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.
// FIXME: this does not actually handle all reborrows. It only detects cases where `*` is the outermost
// projection of the borrowed place, it skips deref'ing raw pointers and it skips `static`.
// All those cases are handled below with shared/mutable borrows.
// Once `const_mut_refs` is stable, we should be able to entirely remove this special case.
// (`const_refs_to_cell` is not needed, we already allow all borrows of indirect places anyway.)
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::Fake(_) => {
PlaceContext::NonMutatingUse(NonMutatingUseContext::FakeBorrow)
}
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::RawPtr(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::RawBorrow)
}
Mutability::Mut => PlaceContext::MutatingUse(MutatingUseContext::RawBorrow),
};
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::Coroutine(def_id, ..) = kind.as_ref()
&& let Some(
coroutine_kind @ hir::CoroutineKind::Desugared(
hir::CoroutineDesugaring::Async,
_,
),
) = self.tcx.coroutine_kind(def_id)
{
self.check_op(ops::Coroutine(coroutine_kind));
}
}
Rvalue::Ref(_, BorrowKind::Mut { .. }, place)
| Rvalue::RawPtr(Mutability::Mut, place) => {
// Inside mutable statics, we allow arbitrary mutable references.
// We've allowed `static mut FOO = &mut [elements];` for a long time (the exact
// reasons why are lost to history), and there is no reason to restrict that to
// arrays and slices.
let is_allowed =
self.const_kind() == hir::ConstContext::Static(hir::Mutability::Mut);
if !is_allowed {
self.check_mut_borrow(
place,
if matches!(rvalue, Rvalue::Ref(..)) {
hir::BorrowKind::Ref
} else {
hir::BorrowKind::Raw
},
);
}
}
Rvalue::Ref(_, BorrowKind::Shared | BorrowKind::Fake(_), place)
| Rvalue::RawPtr(Mutability::Not, 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 the place is indirect, this is basically a reborrow. We have a reborrow
// special case above, but for raw pointers and pointers/references to `static` and
// when the `*` is not the first projection, `place_as_reborrow` does not recognize
// them as such, so we end up here. This should probably be considered a
// `TransientCellBorrow` (we consider the equivalent mutable case a
// `TransientMutBorrow`), but such reborrows got accidentally stabilized already and
// it is too much of a breaking change to take back.
if borrowed_place_has_mut_interior && !place.is_indirect() {
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.
// The good news is that interning will detect if any unexpected mutable
// pointer slips through.
if self.local_is_transient(place.local) {
self.check_op(ops::TransientCellBorrow);
} else {
self.check_op(ops::CellBorrow);
}
}
}
}
}
Rvalue::Cast(
CastKind::PointerCoercion(
PointerCoercion::MutToConstPointer
| PointerCoercion::ArrayToPointer
| PointerCoercion::UnsafeFnPointer
| PointerCoercion::ClosureFnPointer(_)
| PointerCoercion::ReifyFnPointer,
),
_,
_,
) => {
// These are all okay; they only change the type, not the data.
}
Rvalue::Cast(CastKind::PointerCoercion(PointerCoercion::Unsize), _, _) => {
// Unsizing is implemented for CTFE.
}
Rvalue::Cast(CastKind::PointerExposeProvenance, _, _) => {
self.check_op(ops::RawPtrToIntCast);
}
Rvalue::Cast(CastKind::PointerWithExposedProvenance, _, _) => {
// Since no pointer can ever get exposed (rejected above), this is easy to support.
}
Rvalue::Cast(CastKind::DynStar, _, _) => {
// `dyn*` coercion is implemented for CTFE.
}
Rvalue::Cast(_, _, _) => {}
Rvalue::NullaryOp(
NullOp::SizeOf | NullOp::AlignOf | NullOp::OffsetOf(_) | NullOp::UbChecks,
_,
) => {}
Rvalue::ShallowInitBox(_, _) => {}
Rvalue::UnaryOp(_, operand) => {
let ty = operand.ty(self.body, self.tcx);
if is_int_bool_float_or_char(ty) {
// Int, bool, float, and char operations are fine.
} else {
span_bug!(self.span, "non-primitive type in `Rvalue::UnaryOp`: {:?}", ty);
}
}
Rvalue::BinaryOp(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_float_or_char(lhs_ty) && is_int_bool_float_or_char(rhs_ty) {
// Int, bool, float, and char operations are fine.
} else if lhs_ty.is_fn_ptr() || lhs_ty.is_unsafe_ptr() {
assert_matches!(
op,
BinOp::Eq
| BinOp::Ne
| BinOp::Le
| BinOp::Lt
| BinOp::Ge
| BinOp::Gt
| BinOp::Offset
);
self.check_op(ops::RawPtrComparison);
} 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_ref: PlaceRef<'tcx>,
elem: PlaceElem<'tcx>,
context: PlaceContext,
location: Location,
) {
trace!(
"visit_projection_elem: place_ref={:?} elem={:?} \
context={:?} location={:?}",
place_ref, elem, context, location,
);
self.super_projection_elem(place_ref, elem, context, location);
match elem {
ProjectionElem::Deref => {
let base_ty = place_ref.ty(self.body, self.tcx).ty;
if base_ty.is_unsafe_ptr() {
if place_ref.projection.is_empty() {
let decl = &self.body.local_decls[place_ref.local];
// If this is a static, then this is not really dereferencing a pointer,
// just directly accessing a static. That is not subject to any feature
// gates (except for the one about whether statics can even be used, but
// that is checked already by `visit_operand`).
if let LocalInfo::StaticRef { .. } = *decl.local_info() {
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::Subtype(..)
| 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::PlaceMention(..)
| 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, .. }
| TerminatorKind::TailCall { func, args, fn_span, .. } => {
let call_source = match terminator.kind {
TerminatorKind::Call { call_source, .. } => call_source,
TerminatorKind::TailCall { .. } => CallSource::Normal,
_ => unreachable!(),
};
let ConstCx { tcx, body, param_env, .. } = *self.ccx;
let caller = self.def_id();
let fn_ty = func.ty(body, tcx);
let (mut callee, mut fn_args) = match *fn_ty.kind() {
ty::FnDef(def_id, fn_args) => (def_id, fn_args),
ty::FnPtr(..) => {
self.check_op(ops::FnCallIndirect);
return;
}
_ => {
span_bug!(terminator.source_info.span, "invalid callee of type {:?}", fn_ty)
}
};
// Check that all trait bounds that are marked as `~const` can be satisfied.
//
// Typeck only does a "non-const" check since it operates on HIR and cannot distinguish
// which path expressions are getting called on and which path expressions are only used
// as function pointers. This is required for correctness.
let infcx = tcx.infer_ctxt().build();
let ocx = ObligationCtxt::new_with_diagnostics(&infcx);
let predicates = tcx.predicates_of(callee).instantiate(tcx, fn_args);
let cause = ObligationCause::new(
terminator.source_info.span,
self.body.source.def_id().expect_local(),
ObligationCauseCode::WhereClause(callee, DUMMY_SP),
);
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);
}
let mut is_trait = false;
// Attempting to call a trait method?
if tcx.trait_of_item(callee).is_some() {
trace!("attempting to call a trait method");
// trait method calls are only permitted when `effects` is enabled.
// we don't error, since that is handled by typeck. We try to resolve
// the trait into the concrete method, and uses that for const stability
// checks.
// FIXME(effects) we might consider moving const stability checks to typeck as well.
if tcx.features().effects {
is_trait = true;
if let Ok(Some(instance)) =
Instance::try_resolve(tcx, param_env, callee, fn_args)
&& let InstanceKind::Item(def) = instance.def
{
// Resolve a trait method call to its concrete implementation, which may be in a
// `const` trait impl. This is only used for the const stability check below, since
// we want to look at the concrete impl's stability.
fn_args = instance.args;
callee = def;
}
} else {
self.check_op(ops::FnCallNonConst {
caller,
callee,
args: fn_args,
span: *fn_span,
call_source,
feature: Some(if tcx.features().const_trait_impl {
sym::effects
} else {
sym::const_trait_impl
}),
});
return;
}
}
// At this point, we are calling a function, `callee`, whose `DefId` is known...
// `begin_panic` and `#[rustc_const_panic_str]` functions accept generic
// 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 tcx.is_lang_item(callee, LangItem::BeginPanic) {
match args[0].node.ty(&self.ccx.body.local_decls, tcx).kind() {
ty::Ref(_, ty, _) if ty.is_str() => return,
_ => self.check_op(ops::PanicNonStr),
}
}
// const-eval of `#[rustc_const_panic_str]` functions assumes the argument is `&&str`
if tcx.has_attr(callee, sym::rustc_const_panic_str) {
match args[0].node.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 tcx.is_lang_item(callee, LangItem::ExchangeMalloc) {
self.check_op(ops::HeapAllocation);
return;
}
if !tcx.is_const_fn_raw(callee) && !is_trait {
self.check_op(ops::FnCallNonConst {
caller,
callee,
args: fn_args,
span: *fn_span,
call_source,
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, implied_by)) = is_unstable_const_fn(tcx, callee) {
trace!(?gate, "calling unstable const fn");
if self.span.allows_unstable(gate) {
return;
}
if let Some(implied_by_gate) = implied_by
&& self.span.allows_unstable(implied_by_gate)
{
return;
}
// Calling an unstable function *always* requires that the corresponding gate
// (or implied gate) be enabled, even if the function has
// `#[rustc_allow_const_fn_unstable(the_gate)]`.
let gate_declared = |gate| tcx.features().declared(gate);
let feature_gate_declared = gate_declared(gate);
let implied_gate_declared = implied_by.is_some_and(gate_declared);
if !feature_gate_declared && !implied_gate_declared {
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).is_some_and(|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.intrinsic(callee).is_some() {
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, .. } => {
// 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::Yield { .. } => self.check_op(ops::Coroutine(
self.tcx
.coroutine_kind(self.body.source.def_id())
.expect("Only expected to have a yield in a coroutine"),
)),
TerminatorKind::CoroutineDrop => {
span_bug!(
self.body.source_info(location).span,
"We should not encounter TerminatorKind::CoroutineDrop after coroutine transform"
);
}
TerminatorKind::UnwindTerminate(_) => {
// Cleanup blocks are skipped for const checking (see `visit_basic_block_data`).
span_bug!(self.span, "`Terminate` terminator outside of cleanup block")
}
TerminatorKind::Assert { .. }
| TerminatorKind::FalseEdge { .. }
| TerminatorKind::FalseUnwind { .. }
| TerminatorKind::Goto { .. }
| TerminatorKind::UnwindResume
| 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)) => {
// FIXME: why do statics and raw pointers get excluded here? This makes
// some code involving mutable pointers unstable, but it is unclear
// why that code is treated differently from mutable references.
// Once TransientMutBorrow and TransientCellBorrow are stable,
// this can probably be cleaned up without any behavioral changes.
// 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_float_or_char(ty: Ty<'_>) -> bool {
ty.is_bool() || ty.is_integral() || ty.is_char() || ty.is_floating_point()
}
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.dcx().emit_err(UnstableInStable { gate: gate.to_string(), span, attr_span });
}