| // 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 clippy_config::msrvs::Msrv; |
| use hir::LangItem; |
| use rustc_attr::StableSince; |
| use rustc_const_eval::transform::check_consts::ConstCx; |
| use rustc_hir as hir; |
| use rustc_hir::def_id::DefId; |
| use rustc_infer::infer::TyCtxtInferExt; |
| use rustc_infer::traits::Obligation; |
| use rustc_middle::mir::{ |
| Body, CastKind, NonDivergingIntrinsic, NullOp, Operand, Place, ProjectionElem, Rvalue, Statement, StatementKind, |
| Terminator, TerminatorKind, |
| }; |
| use rustc_middle::traits::{BuiltinImplSource, ImplSource, ObligationCause}; |
| use rustc_middle::ty::adjustment::PointerCoercion; |
| use rustc_middle::ty::{self, GenericArgKind, TraitRef, Ty, TyCtxt}; |
| use rustc_semver::RustcVersion; |
| use rustc_span::symbol::sym; |
| use rustc_span::Span; |
| use rustc_trait_selection::traits::{ObligationCtxt, SelectionContext}; |
| use std::borrow::Cow; |
| |
| type McfResult = Result<(), (Span, Cow<'static, str>)>; |
| |
| pub fn is_min_const_fn<'tcx>(tcx: TyCtxt<'tcx>, body: &Body<'tcx>, msrv: &Msrv) -> McfResult { |
| let def_id = body.source.def_id(); |
| |
| 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).instantiate_identity().output().skip_binder(), |
| body.local_decls.iter().next().unwrap().source_info.span, |
| )?; |
| |
| for bb in &*body.basic_blocks { |
| 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::Alias(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 { |
| 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::PointerWithExposedProvenance |
| | CastKind::IntToInt |
| | CastKind::FloatToInt |
| | CastKind::IntToFloat |
| | CastKind::FloatToFloat |
| | CastKind::FnPtrToPtr |
| | CastKind::PtrToPtr |
| | CastKind::PointerCoercion(PointerCoercion::MutToConstPointer | PointerCoercion::ArrayToPointer), |
| operand, |
| _, |
| ) => check_operand(tcx, operand, span, body), |
| Rvalue::Cast( |
| CastKind::PointerCoercion( |
| PointerCoercion::UnsafeFnPointer |
| | PointerCoercion::ClosureFnPointer(_) |
| | PointerCoercion::ReifyFnPointer, |
| ), |
| _, |
| _, |
| ) => Err((span, "function pointer casts are not allowed in const fn".into())), |
| Rvalue::Cast(CastKind::PointerCoercion(PointerCoercion::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::PointerExposeProvenance, _, _) => { |
| Err((span, "casting pointers to ints is unstable in const fn".into())) |
| }, |
| Rvalue::Cast(CastKind::DynStar, _, _) => { |
| // FIXME(dyn-star) |
| unimplemented!() |
| }, |
| Rvalue::Cast(CastKind::Transmute, _, _) => Err(( |
| span, |
| "transmute can attempt to turn pointers into integers, so is unstable in const fn".into(), |
| )), |
| // 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 | NullOp::OffsetOf(_) | NullOp::UbChecks, _) |
| | 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::PlaceMention(..) |
| | StatementKind::Coverage(..) |
| | StatementKind::ConstEvalCounter |
| | StatementKind::Nop => Ok(()), |
| } |
| } |
| |
| fn check_operand<'tcx>(tcx: TyCtxt<'tcx>, operand: &Operand<'tcx>, span: Span, body: &Body<'tcx>) -> McfResult { |
| match operand { |
| Operand::Move(place) => { |
| if !place.projection.as_ref().is_empty() |
| && !is_ty_const_destruct(tcx, place.ty(&body.local_decls, tcx).ty, body) |
| { |
| return Err(( |
| span, |
| "cannot drop locals with a non constant destructor in const fn".into(), |
| )); |
| } |
| |
| check_place(tcx, *place, span, body) |
| }, |
| 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 { |
| for (base, elem) in place.as_ref().iter_projections() { |
| match elem { |
| ProjectionElem::Field(..) => { |
| let base_ty = base.ty(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::Subtype(_) |
| | ProjectionElem::Index(_) => {}, |
| } |
| } |
| |
| Ok(()) |
| } |
| |
| fn check_terminator<'tcx>( |
| tcx: TyCtxt<'tcx>, |
| body: &Body<'tcx>, |
| terminator: &Terminator<'tcx>, |
| msrv: &Msrv, |
| ) -> McfResult { |
| let span = terminator.source_info.span; |
| match &terminator.kind { |
| TerminatorKind::FalseEdge { .. } |
| | TerminatorKind::FalseUnwind { .. } |
| | TerminatorKind::Goto { .. } |
| | TerminatorKind::Return |
| | TerminatorKind::UnwindResume |
| | TerminatorKind::UnwindTerminate(_) |
| | TerminatorKind::Unreachable => Ok(()), |
| TerminatorKind::Drop { place, .. } => { |
| if !is_ty_const_destruct(tcx, place.ty(&body.local_decls, tcx).ty, body) { |
| return Err(( |
| span, |
| "cannot drop locals with a non constant destructor in const fn".into(), |
| )); |
| } |
| Ok(()) |
| }, |
| TerminatorKind::SwitchInt { discr, targets: _ } => check_operand(tcx, discr, span, body), |
| TerminatorKind::CoroutineDrop | TerminatorKind::Yield { .. } => { |
| Err((span, "const fn coroutines are unstable".into())) |
| }, |
| TerminatorKind::Call { |
| func, |
| args, |
| call_source: _, |
| destination: _, |
| target: _, |
| unwind: _, |
| 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, 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.node, span, body)?; |
| } |
| Ok(()) |
| } else { |
| Err((span, "can only call other const fns within const fn".into())) |
| } |
| }, |
| TerminatorKind::Assert { |
| cond, |
| expected: _, |
| msg: _, |
| target: _, |
| unwind: _, |
| } => 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: &Msrv) -> 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. |
| |
| let const_stab_rust_version = match since { |
| StableSince::Version(version) => version, |
| StableSince::Current => rustc_session::RustcVersion::CURRENT, |
| StableSince::Err => return false, |
| }; |
| |
| msrv.meets(RustcVersion::new( |
| u32::from(const_stab_rust_version.major), |
| u32::from(const_stab_rust_version.minor), |
| u32::from(const_stab_rust_version.patch), |
| )) |
| } else { |
| // Unstable const fn with the feature enabled. |
| msrv.current().is_none() |
| } |
| }) |
| } |
| |
| fn is_ty_const_destruct<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>, body: &Body<'tcx>) -> bool { |
| // FIXME(effects, fee1-dead) revert to const destruct once it works again |
| #[expect(unused)] |
| fn is_ty_const_destruct_unused<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>, body: &Body<'tcx>) -> bool { |
| // Avoid selecting for simple cases, such as builtin types. |
| if ty::util::is_trivially_const_drop(ty) { |
| return true; |
| } |
| |
| // FIXME(effects) constness |
| let obligation = Obligation::new( |
| tcx, |
| ObligationCause::dummy_with_span(body.span), |
| ConstCx::new(tcx, body).param_env, |
| TraitRef::from_lang_item(tcx, LangItem::Destruct, body.span, [ty]), |
| ); |
| |
| let infcx = tcx.infer_ctxt().build(); |
| let mut selcx = SelectionContext::new(&infcx); |
| let Some(impl_src) = selcx.select(&obligation).ok().flatten() else { |
| return false; |
| }; |
| |
| if !matches!( |
| impl_src, |
| ImplSource::Builtin(BuiltinImplSource::Misc, _) | ImplSource::Param(_) |
| ) { |
| return false; |
| } |
| |
| let ocx = ObligationCtxt::new(&infcx); |
| ocx.register_obligations(impl_src.nested_obligations()); |
| ocx.select_all_or_error().is_empty() |
| } |
| |
| !ty.needs_drop(tcx, ConstCx::new(tcx, body).param_env) |
| } |