393 lines
16 KiB
Rust
393 lines
16 KiB
Rust
// This code used to be a part of `rustc` but moved to Clippy as a result of
|
|
// https://github.com/rust-lang/rust/issues/76618. Because of that, it contains unused code and some
|
|
// of terminologies might not be relevant in the context of Clippy. Note that its behavior might
|
|
// differ from the time of `rustc` even if the name stays the same.
|
|
|
|
use rustc_hir as hir;
|
|
use rustc_hir::def_id::DefId;
|
|
use rustc_middle::mir::{
|
|
Body, CastKind, NonDivergingIntrinsic, NullOp, Operand, Place, ProjectionElem, Rvalue, Statement, StatementKind,
|
|
Terminator, TerminatorKind,
|
|
};
|
|
use rustc_middle::ty::subst::GenericArgKind;
|
|
use rustc_middle::ty::{self, adjustment::PointerCast, Ty, TyCtxt};
|
|
use rustc_semver::RustcVersion;
|
|
use rustc_span::symbol::sym;
|
|
use rustc_span::Span;
|
|
use std::borrow::Cow;
|
|
|
|
type McfResult = Result<(), (Span, Cow<'static, str>)>;
|
|
|
|
pub fn is_min_const_fn<'a, 'tcx>(tcx: TyCtxt<'tcx>, body: &'a Body<'tcx>, msrv: Option<RustcVersion>) -> McfResult {
|
|
let def_id = body.source.def_id();
|
|
let mut current = def_id;
|
|
loop {
|
|
let predicates = tcx.predicates_of(current);
|
|
for (predicate, _) in predicates.predicates {
|
|
match predicate.kind().skip_binder() {
|
|
ty::PredicateKind::RegionOutlives(_)
|
|
| ty::PredicateKind::TypeOutlives(_)
|
|
| ty::PredicateKind::WellFormed(_)
|
|
| ty::PredicateKind::Projection(_)
|
|
| ty::PredicateKind::ConstEvaluatable(..)
|
|
| ty::PredicateKind::ConstEquate(..)
|
|
| ty::PredicateKind::Trait(..)
|
|
| ty::PredicateKind::TypeWellFormedFromEnv(..) => continue,
|
|
ty::PredicateKind::ObjectSafe(_) => panic!("object safe predicate on function: {predicate:#?}"),
|
|
ty::PredicateKind::ClosureKind(..) => panic!("closure kind predicate on function: {predicate:#?}"),
|
|
ty::PredicateKind::Subtype(_) => panic!("subtype predicate on function: {predicate:#?}"),
|
|
ty::PredicateKind::Coerce(_) => panic!("coerce predicate on function: {predicate:#?}"),
|
|
}
|
|
}
|
|
match predicates.parent {
|
|
Some(parent) => current = parent,
|
|
None => break,
|
|
}
|
|
}
|
|
|
|
for local in &body.local_decls {
|
|
check_ty(tcx, local.ty, local.source_info.span)?;
|
|
}
|
|
// impl trait is gone in MIR, so check the return type manually
|
|
check_ty(
|
|
tcx,
|
|
tcx.fn_sig(def_id).output().skip_binder(),
|
|
body.local_decls.iter().next().unwrap().source_info.span,
|
|
)?;
|
|
|
|
for bb in body.basic_blocks.iter() {
|
|
check_terminator(tcx, body, bb.terminator(), msrv)?;
|
|
for stmt in &bb.statements {
|
|
check_statement(tcx, body, def_id, stmt)?;
|
|
}
|
|
}
|
|
Ok(())
|
|
}
|
|
|
|
fn check_ty<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>, span: Span) -> McfResult {
|
|
for arg in ty.walk() {
|
|
let ty = match arg.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) => {
|
|
return Err((span, "mutable references in const fn are unstable".into()));
|
|
},
|
|
ty::Opaque(..) => return Err((span, "`impl Trait` in const fn is unstable".into())),
|
|
ty::FnPtr(..) => {
|
|
return Err((span, "function pointers in const fn are unstable".into()));
|
|
},
|
|
ty::Dynamic(preds, _, _) => {
|
|
for pred in preds.iter() {
|
|
match pred.skip_binder() {
|
|
ty::ExistentialPredicate::AutoTrait(_) | ty::ExistentialPredicate::Projection(_) => {
|
|
return Err((
|
|
span,
|
|
"trait bounds other than `Sized` \
|
|
on const fn parameters are unstable"
|
|
.into(),
|
|
));
|
|
},
|
|
ty::ExistentialPredicate::Trait(trait_ref) => {
|
|
if Some(trait_ref.def_id) != tcx.lang_items().sized_trait() {
|
|
return Err((
|
|
span,
|
|
"trait bounds other than `Sized` \
|
|
on const fn parameters are unstable"
|
|
.into(),
|
|
));
|
|
}
|
|
},
|
|
}
|
|
}
|
|
},
|
|
_ => {},
|
|
}
|
|
}
|
|
Ok(())
|
|
}
|
|
|
|
fn check_rvalue<'tcx>(
|
|
tcx: TyCtxt<'tcx>,
|
|
body: &Body<'tcx>,
|
|
def_id: DefId,
|
|
rvalue: &Rvalue<'tcx>,
|
|
span: Span,
|
|
) -> McfResult {
|
|
match rvalue {
|
|
Rvalue::ThreadLocalRef(_) => Err((span, "cannot access thread local storage in const fn".into())),
|
|
Rvalue::Len(place) | Rvalue::Discriminant(place) | Rvalue::Ref(_, _, place) | Rvalue::AddressOf(_, place) => {
|
|
check_place(tcx, *place, span, body)
|
|
},
|
|
Rvalue::CopyForDeref(place) => check_place(tcx, *place, span, body),
|
|
Rvalue::Repeat(operand, _)
|
|
| Rvalue::Use(operand)
|
|
| Rvalue::Cast(
|
|
CastKind::PointerFromExposedAddress
|
|
| CastKind::Misc
|
|
| CastKind::Pointer(PointerCast::MutToConstPointer | PointerCast::ArrayToPointer),
|
|
operand,
|
|
_,
|
|
) => check_operand(tcx, operand, span, body),
|
|
Rvalue::Cast(
|
|
CastKind::Pointer(
|
|
PointerCast::UnsafeFnPointer | PointerCast::ClosureFnPointer(_) | PointerCast::ReifyFnPointer,
|
|
),
|
|
_,
|
|
_,
|
|
) => Err((span, "function pointer casts are not allowed in const fn".into())),
|
|
Rvalue::Cast(CastKind::Pointer(PointerCast::Unsize), op, cast_ty) => {
|
|
let pointee_ty = if let Some(deref_ty) = cast_ty.builtin_deref(true) {
|
|
deref_ty.ty
|
|
} else {
|
|
// We cannot allow this for now.
|
|
return Err((span, "unsizing casts are only allowed for references right now".into()));
|
|
};
|
|
let unsized_ty = tcx.struct_tail_erasing_lifetimes(pointee_ty, tcx.param_env(def_id));
|
|
if let ty::Slice(_) | ty::Str = unsized_ty.kind() {
|
|
check_operand(tcx, op, span, body)?;
|
|
// Casting/coercing things to slices is fine.
|
|
Ok(())
|
|
} else {
|
|
// We just can't allow trait objects until we have figured out trait method calls.
|
|
Err((span, "unsizing casts are not allowed in const fn".into()))
|
|
}
|
|
},
|
|
Rvalue::Cast(CastKind::PointerExposeAddress, _, _) => {
|
|
Err((span, "casting pointers to ints is unstable in const fn".into()))
|
|
},
|
|
Rvalue::Cast(CastKind::DynStar, _, _) => {
|
|
// FIXME(dyn-star)
|
|
unimplemented!()
|
|
},
|
|
// binops are fine on integers
|
|
Rvalue::BinaryOp(_, box (lhs, rhs)) | Rvalue::CheckedBinaryOp(_, box (lhs, rhs)) => {
|
|
check_operand(tcx, lhs, span, body)?;
|
|
check_operand(tcx, rhs, span, body)?;
|
|
let ty = lhs.ty(body, tcx);
|
|
if ty.is_integral() || ty.is_bool() || ty.is_char() {
|
|
Ok(())
|
|
} else {
|
|
Err((
|
|
span,
|
|
"only int, `bool` and `char` operations are stable in const fn".into(),
|
|
))
|
|
}
|
|
},
|
|
Rvalue::NullaryOp(NullOp::SizeOf | NullOp::AlignOf, _) | Rvalue::ShallowInitBox(_, _) => Ok(()),
|
|
Rvalue::UnaryOp(_, operand) => {
|
|
let ty = operand.ty(body, tcx);
|
|
if ty.is_integral() || ty.is_bool() {
|
|
check_operand(tcx, operand, span, body)
|
|
} else {
|
|
Err((span, "only int and `bool` operations are stable in const fn".into()))
|
|
}
|
|
},
|
|
Rvalue::Aggregate(_, operands) => {
|
|
for operand in operands {
|
|
check_operand(tcx, operand, span, body)?;
|
|
}
|
|
Ok(())
|
|
},
|
|
}
|
|
}
|
|
|
|
fn check_statement<'tcx>(
|
|
tcx: TyCtxt<'tcx>,
|
|
body: &Body<'tcx>,
|
|
def_id: DefId,
|
|
statement: &Statement<'tcx>,
|
|
) -> McfResult {
|
|
let span = statement.source_info.span;
|
|
match &statement.kind {
|
|
StatementKind::Assign(box (place, rval)) => {
|
|
check_place(tcx, *place, span, body)?;
|
|
check_rvalue(tcx, body, def_id, rval, span)
|
|
},
|
|
|
|
StatementKind::FakeRead(box (_, place)) => check_place(tcx, *place, span, body),
|
|
// just an assignment
|
|
StatementKind::SetDiscriminant { place, .. } | StatementKind::Deinit(place) => {
|
|
check_place(tcx, **place, span, body)
|
|
},
|
|
|
|
StatementKind::Intrinsic(box NonDivergingIntrinsic::Assume(op)) => check_operand(tcx, op, span, body),
|
|
|
|
StatementKind::Intrinsic(box NonDivergingIntrinsic::CopyNonOverlapping(
|
|
rustc_middle::mir::CopyNonOverlapping { dst, src, count },
|
|
)) => {
|
|
check_operand(tcx, dst, span, body)?;
|
|
check_operand(tcx, src, span, body)?;
|
|
check_operand(tcx, count, span, body)
|
|
},
|
|
// These are all NOPs
|
|
StatementKind::StorageLive(_)
|
|
| StatementKind::StorageDead(_)
|
|
| StatementKind::Retag { .. }
|
|
| StatementKind::AscribeUserType(..)
|
|
| StatementKind::Coverage(..)
|
|
| StatementKind::Nop => Ok(()),
|
|
}
|
|
}
|
|
|
|
fn check_operand<'tcx>(tcx: TyCtxt<'tcx>, operand: &Operand<'tcx>, span: Span, body: &Body<'tcx>) -> McfResult {
|
|
match operand {
|
|
Operand::Move(place) | Operand::Copy(place) => check_place(tcx, *place, span, body),
|
|
Operand::Constant(c) => match c.check_static_ptr(tcx) {
|
|
Some(_) => Err((span, "cannot access `static` items in const fn".into())),
|
|
None => Ok(()),
|
|
},
|
|
}
|
|
}
|
|
|
|
fn check_place<'tcx>(tcx: TyCtxt<'tcx>, place: Place<'tcx>, span: Span, body: &Body<'tcx>) -> McfResult {
|
|
let mut cursor = place.projection.as_ref();
|
|
while let [ref proj_base @ .., elem] = *cursor {
|
|
cursor = proj_base;
|
|
match elem {
|
|
ProjectionElem::Field(..) => {
|
|
let base_ty = Place::ty_from(place.local, proj_base, body, tcx).ty;
|
|
if let Some(def) = base_ty.ty_adt_def() {
|
|
// No union field accesses in `const fn`
|
|
if def.is_union() {
|
|
return Err((span, "accessing union fields is unstable".into()));
|
|
}
|
|
}
|
|
},
|
|
ProjectionElem::ConstantIndex { .. }
|
|
| ProjectionElem::OpaqueCast(..)
|
|
| ProjectionElem::Downcast(..)
|
|
| ProjectionElem::Subslice { .. }
|
|
| ProjectionElem::Deref
|
|
| ProjectionElem::Index(_) => {},
|
|
}
|
|
}
|
|
|
|
Ok(())
|
|
}
|
|
|
|
fn check_terminator<'a, 'tcx>(
|
|
tcx: TyCtxt<'tcx>,
|
|
body: &'a Body<'tcx>,
|
|
terminator: &Terminator<'tcx>,
|
|
msrv: Option<RustcVersion>,
|
|
) -> McfResult {
|
|
let span = terminator.source_info.span;
|
|
match &terminator.kind {
|
|
TerminatorKind::FalseEdge { .. }
|
|
| TerminatorKind::FalseUnwind { .. }
|
|
| TerminatorKind::Goto { .. }
|
|
| TerminatorKind::Return
|
|
| TerminatorKind::Resume
|
|
| TerminatorKind::Unreachable => Ok(()),
|
|
|
|
TerminatorKind::Drop { place, .. } => check_place(tcx, *place, span, body),
|
|
TerminatorKind::DropAndReplace { place, value, .. } => {
|
|
check_place(tcx, *place, span, body)?;
|
|
check_operand(tcx, value, span, body)
|
|
},
|
|
|
|
TerminatorKind::SwitchInt {
|
|
discr,
|
|
switch_ty: _,
|
|
targets: _,
|
|
} => check_operand(tcx, discr, span, body),
|
|
|
|
TerminatorKind::Abort => Err((span, "abort is not stable in const fn".into())),
|
|
TerminatorKind::GeneratorDrop | TerminatorKind::Yield { .. } => {
|
|
Err((span, "const fn generators are unstable".into()))
|
|
},
|
|
|
|
TerminatorKind::Call {
|
|
func,
|
|
args,
|
|
from_hir_call: _,
|
|
destination: _,
|
|
target: _,
|
|
cleanup: _,
|
|
fn_span: _,
|
|
} => {
|
|
let fn_ty = func.ty(body, tcx);
|
|
if let ty::FnDef(fn_def_id, _) = *fn_ty.kind() {
|
|
if !is_const_fn(tcx, fn_def_id, msrv) {
|
|
return Err((
|
|
span,
|
|
format!(
|
|
"can only call other `const fn` within a `const fn`, \
|
|
but `{func:?}` is not stable as `const fn`",
|
|
)
|
|
.into(),
|
|
));
|
|
}
|
|
|
|
// HACK: This is to "unstabilize" the `transmute` intrinsic
|
|
// within const fns. `transmute` is allowed in all other const contexts.
|
|
// This won't really scale to more intrinsics or functions. Let's allow const
|
|
// transmutes in const fn before we add more hacks to this.
|
|
if tcx.is_intrinsic(fn_def_id) && tcx.item_name(fn_def_id) == sym::transmute {
|
|
return Err((
|
|
span,
|
|
"can only call `transmute` from const items, not `const fn`".into(),
|
|
));
|
|
}
|
|
|
|
check_operand(tcx, func, span, body)?;
|
|
|
|
for arg in args {
|
|
check_operand(tcx, arg, span, body)?;
|
|
}
|
|
Ok(())
|
|
} else {
|
|
Err((span, "can only call other const fns within const fn".into()))
|
|
}
|
|
},
|
|
|
|
TerminatorKind::Assert {
|
|
cond,
|
|
expected: _,
|
|
msg: _,
|
|
target: _,
|
|
cleanup: _,
|
|
} => check_operand(tcx, cond, span, body),
|
|
|
|
TerminatorKind::InlineAsm { .. } => Err((span, "cannot use inline assembly in const fn".into())),
|
|
}
|
|
}
|
|
|
|
fn is_const_fn(tcx: TyCtxt<'_>, def_id: DefId, msrv: Option<RustcVersion>) -> bool {
|
|
tcx.is_const_fn(def_id)
|
|
&& tcx.lookup_const_stability(def_id).map_or(true, |const_stab| {
|
|
if let rustc_attr::StabilityLevel::Stable { since, .. } = const_stab.level {
|
|
// Checking MSRV is manually necessary because `rustc` has no such concept. This entire
|
|
// function could be removed if `rustc` provided a MSRV-aware version of `is_const_fn`.
|
|
// as a part of an unimplemented MSRV check https://github.com/rust-lang/rust/issues/65262.
|
|
|
|
// HACK(nilstrieb): CURRENT_RUSTC_VERSION can return versions like 1.66.0-dev. `rustc-semver`
|
|
// doesn't accept the `-dev` version number so we have to strip it
|
|
// off.
|
|
let short_version = since
|
|
.as_str()
|
|
.split('-')
|
|
.next()
|
|
.expect("rustc_attr::StabilityLevel::Stable::since` is empty");
|
|
|
|
let since = rustc_span::Symbol::intern(short_version);
|
|
|
|
crate::meets_msrv(
|
|
msrv,
|
|
RustcVersion::parse(since.as_str()).unwrap_or_else(|err| {
|
|
panic!("`rustc_attr::StabilityLevel::Stable::since` is ill-formatted: `{since}`, {err:?}")
|
|
}),
|
|
)
|
|
} else {
|
|
// Unstable const fn with the feature enabled.
|
|
msrv.is_none()
|
|
}
|
|
})
|
|
}
|