diff options
Diffstat (limited to 'src/tools/clippy/clippy_utils/src/qualify_min_const_fn.rs')
| -rw-r--r-- | src/tools/clippy/clippy_utils/src/qualify_min_const_fn.rs | 371 |
1 files changed, 371 insertions, 0 deletions
diff --git a/src/tools/clippy/clippy_utils/src/qualify_min_const_fn.rs b/src/tools/clippy/clippy_utils/src/qualify_min_const_fn.rs new file mode 100644 index 000000000..3bf75bcbe --- /dev/null +++ b/src/tools/clippy/clippy_utils/src/qualify_min_const_fn.rs @@ -0,0 +1,371 @@ +// 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, 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() { + 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())) + }, + // 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::CopyNonOverlapping(box 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::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 `{:?}` is not stable as `const fn`", + func, + ) + .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. + crate::meets_msrv( + msrv, + RustcVersion::parse(since.as_str()) + .expect("`rustc_attr::StabilityLevel::Stable::since` is ill-formatted"), + ) + } else { + // Unstable const fn with the feature enabled. + msrv.is_none() + } + }) +} |