rustc_const_eval/check_consts/check.rs
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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::num::NonZero;
use std::ops::Deref;
use rustc_attr::{ConstStability, StabilityLevel};
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_middle::mir::visit::Visitor;
use rustc_middle::mir::*;
use rustc_middle::span_bug;
use rustc_middle::ty::adjustment::PointerCoercion;
use rustc_middle::ty::{self, Ty, TypeVisitableExt};
use rustc_mir_dataflow::Analysis;
use rustc_mir_dataflow::impls::MaybeStorageLive;
use rustc_mir_dataflow::storage::always_storage_live_locals;
use rustc_span::{Span, Symbol, sym};
use rustc_trait_selection::traits::{
Obligation, ObligationCause, ObligationCauseCode, ObligationCtxt,
};
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::check_consts::is_safe_to_expose_on_stable_const_fn;
use crate::errors;
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
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)
.iterate_to_fixpoint(tcx, body, None)
.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(crate) 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)
.iterate_to_fixpoint(tcx, body, None)
.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.
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)
.iterate_to_fixpoint(tcx, body, None)
.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,
}
}
}
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;
}
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))
.iterate_to_fixpoint(ccx.tcx, &ccx.body, None)
.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::Unstable {
gate,
safe_to_expose_on_stable,
is_function_call,
gate_already_checked,
} if gate_already_checked || self.tcx.features().enabled(gate) => {
if gate_already_checked {
assert!(
!safe_to_expose_on_stable,
"setting `gate_already_checked` without `safe_to_expose_on_stable` makes no sense"
);
}
// Generally this is allowed since the feature gate is enabled -- except
// if this function wants to be safe-to-expose-on-stable.
if !safe_to_expose_on_stable
&& self.enforce_recursive_const_stability()
&& !super::rustc_allow_const_fn_unstable(self.tcx, self.def_id(), gate)
{
emit_unstable_in_stable_exposed_error(self.ccx, span, gate, is_function_call);
}
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);
self.tcx.dcx().span_delayed_bug(
span,
"compilation must fail when there is a secondary const checker error",
);
}
}
}
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);
}
}
/// Returns whether this place can possibly escape the evaluation of the current const/static
/// initializer. The check assumes that all already existing pointers and references point to
/// non-escaping places.
fn place_may_escape(&mut self, place: &Place<'_>) -> bool {
let is_transient = 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 => true,
_ => {
// 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.
// If anything slips through, there's no safety net -- safe code can create
// references to variants of `!Freeze` enums as long as that variant is `Freeze`, so
// interning can't protect us here. (There *is* a safety net for mutable references
// though, interning will ICE if we miss something here.)
place.is_indirect() || self.local_is_transient(place.local)
}
};
// Transient places cannot possibly escape because the place doesn't exist any more at the
// end of evaluation.
!is_transient
}
/// Returns whether there are const-conditions.
fn revalidate_conditional_constness(
&mut self,
callee: DefId,
callee_args: ty::GenericArgsRef<'tcx>,
call_span: Span,
) -> bool {
let tcx = self.tcx;
if !tcx.is_conditionally_const(callee) {
return false;
}
let const_conditions = tcx.const_conditions(callee).instantiate(tcx, callee_args);
if const_conditions.is_empty() {
return false;
}
let (infcx, param_env) = tcx.infer_ctxt().build_with_typing_env(self.body.typing_env(tcx));
let ocx = ObligationCtxt::new_with_diagnostics(&infcx);
let body_id = self.body.source.def_id().expect_local();
let host_polarity = match self.const_kind() {
hir::ConstContext::ConstFn => ty::BoundConstness::Maybe,
hir::ConstContext::Static(_) | hir::ConstContext::Const { .. } => {
ty::BoundConstness::Const
}
};
let const_conditions =
ocx.normalize(&ObligationCause::misc(call_span, body_id), param_env, const_conditions);
ocx.register_obligations(const_conditions.into_iter().map(|(trait_ref, span)| {
Obligation::new(
tcx,
ObligationCause::new(
call_span,
body_id,
ObligationCauseCode::WhereClause(callee, span),
),
param_env,
trait_ref.to_host_effect_clause(tcx, host_polarity),
)
}));
let errors = ocx.select_all_or_error();
if !errors.is_empty() {
tcx.dcx()
.span_delayed_bug(call_span, "this should have reported a ~const error in HIR");
}
true
}
}
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);
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.place_may_escape(place) {
self.check_op(ops::EscapingMutBorrow(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 borrowed_place_has_mut_interior && self.place_may_escape(place) {
self.check_op(ops::EscapingCellBorrow);
}
}
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 | PointerCoercion::DynStar, _),
_,
_,
) => {
// Unsizing and `dyn*` coercions are 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(_, _, _) => {}
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_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::BackwardIncompatibleDropHint { .. }
| 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, .. } = *self.ccx;
let fn_ty = func.ty(body, tcx);
let (callee, fn_args) = match *fn_ty.kind() {
ty::FnDef(def_id, fn_args) => (def_id, fn_args),
ty::FnPtr(..) => {
self.check_op(ops::FnCallIndirect);
// We can get here without an error in miri-unleashed mode... might as well
// skip the rest of the checks as well then.
return;
}
_ => {
span_bug!(terminator.source_info.span, "invalid callee of type {:?}", fn_ty)
}
};
let has_const_conditions =
self.revalidate_conditional_constness(callee, fn_args, *fn_span);
// Attempting to call a trait method?
if let Some(trait_did) = tcx.trait_of_item(callee) {
// We can't determine the actual callee here, so we have to do different checks
// than usual.
trace!("attempting to call a trait method");
let trait_is_const = tcx.is_const_trait(trait_did);
if trait_is_const {
// Trait calls are always conditionally-const.
self.check_op(ops::ConditionallyConstCall { callee, args: fn_args });
// FIXME(const_trait_impl): do a more fine-grained check whether this
// particular trait can be const-stably called.
} else {
// Not even a const trait.
self.check_op(ops::FnCallNonConst {
callee,
args: fn_args,
span: *fn_span,
call_source,
});
}
// That's all we can check here.
return;
}
// Even if we know the callee, ensure we can use conditionally-const calls.
if has_const_conditions {
self.check_op(ops::ConditionallyConstCall { callee, args: fn_args });
}
// 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() => {}
_ => self.check_op(ops::PanicNonStr),
}
// Allow this call, skip all the checks below.
return;
}
// 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()) =>
{}
_ => {
self.check_op(ops::PanicNonStr);
}
}
// Allow this call, skip all the checks below.
return;
}
// This can be called on stable via the `vec!` macro.
if tcx.is_lang_item(callee, LangItem::ExchangeMalloc) {
self.check_op(ops::HeapAllocation);
// Allow this call, skip all the checks below.
return;
}
// Intrinsics are language primitives, not regular calls, so treat them separately.
if let Some(intrinsic) = tcx.intrinsic(callee) {
if !tcx.is_const_fn(callee) {
// Non-const intrinsic.
self.check_op(ops::IntrinsicNonConst { name: intrinsic.name });
// If we allowed this, we're in miri-unleashed mode, so we might
// as well skip the remaining checks.
return;
}
// We use `intrinsic.const_stable` to determine if this can be safely exposed to
// stable code, rather than `const_stable_indirect`. This is to make
// `#[rustc_const_stable_indirect]` an attribute that is always safe to add.
// We also ask is_safe_to_expose_on_stable_const_fn; this determines whether the intrinsic
// fallback body is safe to expose on stable.
let is_const_stable = intrinsic.const_stable
|| (!intrinsic.must_be_overridden
&& is_safe_to_expose_on_stable_const_fn(tcx, callee));
match tcx.lookup_const_stability(callee) {
None => {
// This doesn't need a separate const-stability check -- const-stability equals
// regular stability, and regular stability is checked separately.
// However, we *do* have to worry about *recursive* const stability.
if !is_const_stable && self.enforce_recursive_const_stability() {
self.dcx().emit_err(errors::UnmarkedIntrinsicExposed {
span: self.span,
def_path: self.tcx.def_path_str(callee),
});
}
}
Some(ConstStability {
level: StabilityLevel::Unstable { .. },
feature,
..
}) => {
self.check_op(ops::IntrinsicUnstable {
name: intrinsic.name,
feature,
const_stable_indirect: is_const_stable,
});
}
Some(ConstStability { level: StabilityLevel::Stable { .. }, .. }) => {
// All good. Note that a `#[rustc_const_stable]` intrinsic (meaning it
// can be *directly* invoked from stable const code) does not always
// have the `#[rustc_intrinsic_const_stable_indirect]` attribute (which controls
// exposing an intrinsic indirectly); we accept this call anyway.
}
}
// This completes the checks for intrinsics.
return;
}
if !tcx.is_const_fn(callee) {
self.check_op(ops::FnCallNonConst {
callee,
args: fn_args,
span: *fn_span,
call_source,
});
// If we allowed this, we're in miri-unleashed mode, so we might
// as well skip the remaining checks.
return;
}
// Finally, stability for regular function calls -- this is the big one.
match tcx.lookup_const_stability(callee) {
Some(ConstStability { level: StabilityLevel::Stable { .. }, .. }) => {
// All good.
}
None => {
// This doesn't need a separate const-stability check -- const-stability equals
// regular stability, and regular stability is checked separately.
// However, we *do* have to worry about *recursive* const stability.
if self.enforce_recursive_const_stability()
&& !is_safe_to_expose_on_stable_const_fn(tcx, callee)
{
self.dcx().emit_err(errors::UnmarkedConstFnExposed {
span: self.span,
def_path: self.tcx.def_path_str(callee),
});
}
}
Some(ConstStability {
level: StabilityLevel::Unstable { implied_by: implied_feature, issue, .. },
feature,
..
}) => {
// An unstable const fn with a feature gate.
let callee_safe_to_expose_on_stable =
is_safe_to_expose_on_stable_const_fn(tcx, callee);
// We only honor `span.allows_unstable` aka `#[allow_internal_unstable]` if
// the callee is safe to expose, to avoid bypassing recursive stability.
// This is not ideal since it means the user sees an error, not the macro
// author, but that's also the case if one forgets to set
// `#[allow_internal_unstable]` in the first place. Note that this cannot be
// integrated in the check below since we want to enforce
// `callee_safe_to_expose_on_stable` even if
// `!self.enforce_recursive_const_stability()`.
if (self.span.allows_unstable(feature)
|| implied_feature.is_some_and(|f| self.span.allows_unstable(f)))
&& callee_safe_to_expose_on_stable
{
return;
}
// We can't use `check_op` to check whether the feature is enabled because
// the logic is a bit different than elsewhere: local functions don't need
// the feature gate, and there might be an "implied" gate that also suffices
// to allow this.
let feature_enabled = callee.is_local()
|| tcx.features().enabled(feature)
|| implied_feature.is_some_and(|f| tcx.features().enabled(f))
|| {
// When we're compiling the compiler itself we may pull in
// crates from crates.io, but those crates may depend on other
// crates also pulled in from crates.io. We want to ideally be
// able to compile everything without requiring upstream
// modifications, so in the case that this looks like a
// `rustc_private` crate (e.g., a compiler crate) and we also have
// the `-Z force-unstable-if-unmarked` flag present (we're
// compiling a compiler crate), then let this missing feature
// annotation slide.
// This matches what we do in `eval_stability_allow_unstable` for
// regular stability.
feature == sym::rustc_private
&& issue == NonZero::new(27812)
&& self.tcx.sess.opts.unstable_opts.force_unstable_if_unmarked
};
// Even if the feature is enabled, we still need check_op to double-check
// this if the callee is not safe to expose on stable.
if !feature_enabled || !callee_safe_to_expose_on_stable {
self.check_op(ops::FnCallUnstable {
def_id: callee,
feature,
feature_enabled,
safe_to_expose_on_stable: callee_safe_to_expose_on_stable,
});
}
}
}
}
// 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 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_exposed_error(
ccx: &ConstCx<'_, '_>,
span: Span,
gate: Symbol,
is_function_call: bool,
) -> ErrorGuaranteed {
let attr_span = ccx.tcx.def_span(ccx.def_id()).shrink_to_lo();
ccx.dcx().emit_err(errors::UnstableInStableExposed {
gate: gate.to_string(),
span,
attr_span,
is_function_call,
is_function_call2: is_function_call,
})
}