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| 1 | +//! A subset of a mir body used for const evaluatability checking. |
| 2 | +use crate::mir; |
| 3 | +use crate::ty::visit::TypeVisitable; |
| 4 | +use crate::ty::{self, subst::Subst, DelaySpanBugEmitted, EarlyBinder, SubstsRef, Ty, TyCtxt}; |
| 5 | +use rustc_errors::ErrorGuaranteed; |
| 6 | +use rustc_hir::def_id::DefId; |
| 7 | +use std::cmp; |
| 8 | +use std::ops::ControlFlow; |
| 9 | + |
| 10 | +rustc_index::newtype_index! { |
| 11 | + /// An index into an `AbstractConst`. |
| 12 | + pub struct NodeId { |
| 13 | + derive [HashStable] |
| 14 | + DEBUG_FORMAT = "n{}", |
| 15 | + } |
| 16 | +} |
| 17 | + |
| 18 | +/// A tree representing an anonymous constant. |
| 19 | +/// |
| 20 | +/// This is only able to represent a subset of `MIR`, |
| 21 | +/// and should not leak any information about desugarings. |
| 22 | +#[derive(Debug, Clone, Copy)] |
| 23 | +pub struct AbstractConst<'tcx> { |
| 24 | + // FIXME: Consider adding something like `IndexSlice` |
| 25 | + // and use this here. |
| 26 | + inner: &'tcx [Node<'tcx>], |
| 27 | + substs: SubstsRef<'tcx>, |
| 28 | +} |
| 29 | + |
| 30 | +impl<'tcx> AbstractConst<'tcx> { |
| 31 | + pub fn new( |
| 32 | + tcx: TyCtxt<'tcx>, |
| 33 | + uv: ty::Unevaluated<'tcx, ()>, |
| 34 | + ) -> Result<Option<AbstractConst<'tcx>>, ErrorGuaranteed> { |
| 35 | + let inner = tcx.thir_abstract_const_opt_const_arg(uv.def)?; |
| 36 | + debug!("AbstractConst::new({:?}) = {:?}", uv, inner); |
| 37 | + Ok(inner.map(|inner| AbstractConst { inner, substs: tcx.erase_regions(uv.substs) })) |
| 38 | + } |
| 39 | + |
| 40 | + pub fn from_const( |
| 41 | + tcx: TyCtxt<'tcx>, |
| 42 | + ct: ty::Const<'tcx>, |
| 43 | + ) -> Result<Option<AbstractConst<'tcx>>, ErrorGuaranteed> { |
| 44 | + match ct.kind() { |
| 45 | + ty::ConstKind::Unevaluated(uv) => AbstractConst::new(tcx, uv.shrink()), |
| 46 | + ty::ConstKind::Error(DelaySpanBugEmitted { reported, .. }) => Err(reported), |
| 47 | + _ => Ok(None), |
| 48 | + } |
| 49 | + } |
| 50 | + |
| 51 | + #[inline] |
| 52 | + pub fn subtree(self, node: NodeId) -> AbstractConst<'tcx> { |
| 53 | + AbstractConst { inner: &self.inner[..=node.index()], substs: self.substs } |
| 54 | + } |
| 55 | + |
| 56 | + #[inline] |
| 57 | + pub fn root(self, tcx: TyCtxt<'tcx>) -> Node<'tcx> { |
| 58 | + let node = self.inner.last().copied().unwrap(); |
| 59 | + match node { |
| 60 | + Node::Leaf(leaf) => Node::Leaf(EarlyBinder(leaf).subst(tcx, self.substs)), |
| 61 | + Node::Cast(kind, operand, ty) => { |
| 62 | + Node::Cast(kind, operand, EarlyBinder(ty).subst(tcx, self.substs)) |
| 63 | + } |
| 64 | + // Don't perform substitution on the following as they can't directly contain generic params |
| 65 | + Node::Binop(_, _, _) | Node::UnaryOp(_, _) | Node::FunctionCall(_, _) => node, |
| 66 | + } |
| 67 | + } |
| 68 | + |
| 69 | + pub fn unify_failure_kind(self, tcx: TyCtxt<'tcx>) -> FailureKind { |
| 70 | + let mut failure_kind = FailureKind::Concrete; |
| 71 | + walk_abstract_const::<!, _>(tcx, self, |node| { |
| 72 | + match node.root(tcx) { |
| 73 | + Node::Leaf(leaf) => { |
| 74 | + if leaf.has_infer_types_or_consts() { |
| 75 | + failure_kind = FailureKind::MentionsInfer; |
| 76 | + } else if leaf.has_param_types_or_consts() { |
| 77 | + failure_kind = cmp::min(failure_kind, FailureKind::MentionsParam); |
| 78 | + } |
| 79 | + } |
| 80 | + Node::Cast(_, _, ty) => { |
| 81 | + if ty.has_infer_types_or_consts() { |
| 82 | + failure_kind = FailureKind::MentionsInfer; |
| 83 | + } else if ty.has_param_types_or_consts() { |
| 84 | + failure_kind = cmp::min(failure_kind, FailureKind::MentionsParam); |
| 85 | + } |
| 86 | + } |
| 87 | + Node::Binop(_, _, _) | Node::UnaryOp(_, _) | Node::FunctionCall(_, _) => {} |
| 88 | + } |
| 89 | + ControlFlow::CONTINUE |
| 90 | + }); |
| 91 | + failure_kind |
| 92 | + } |
| 93 | +} |
| 94 | + |
| 95 | +#[derive(Debug, Clone, Copy, PartialEq, Eq, HashStable, TyEncodable, TyDecodable)] |
| 96 | +pub enum CastKind { |
| 97 | + /// thir::ExprKind::As |
| 98 | + As, |
| 99 | + /// thir::ExprKind::Use |
| 100 | + Use, |
| 101 | +} |
| 102 | + |
| 103 | +/// A node of an `AbstractConst`. |
| 104 | +#[derive(Debug, Clone, Copy, PartialEq, Eq, HashStable, TyEncodable, TyDecodable)] |
| 105 | +pub enum Node<'tcx> { |
| 106 | + Leaf(ty::Const<'tcx>), |
| 107 | + Binop(mir::BinOp, NodeId, NodeId), |
| 108 | + UnaryOp(mir::UnOp, NodeId), |
| 109 | + FunctionCall(NodeId, &'tcx [NodeId]), |
| 110 | + Cast(CastKind, NodeId, Ty<'tcx>), |
| 111 | +} |
| 112 | + |
| 113 | +#[derive(Debug, Copy, Clone, PartialEq, Eq, HashStable, TyEncodable, TyDecodable)] |
| 114 | +pub enum NotConstEvaluatable { |
| 115 | + Error(ErrorGuaranteed), |
| 116 | + MentionsInfer, |
| 117 | + MentionsParam, |
| 118 | +} |
| 119 | + |
| 120 | +impl From<ErrorGuaranteed> for NotConstEvaluatable { |
| 121 | + fn from(e: ErrorGuaranteed) -> NotConstEvaluatable { |
| 122 | + NotConstEvaluatable::Error(e) |
| 123 | + } |
| 124 | +} |
| 125 | + |
| 126 | +TrivialTypeTraversalAndLiftImpls! { |
| 127 | + NotConstEvaluatable, |
| 128 | +} |
| 129 | + |
| 130 | +impl<'tcx> TyCtxt<'tcx> { |
| 131 | + #[inline] |
| 132 | + pub fn thir_abstract_const_opt_const_arg( |
| 133 | + self, |
| 134 | + def: ty::WithOptConstParam<DefId>, |
| 135 | + ) -> Result<Option<&'tcx [Node<'tcx>]>, ErrorGuaranteed> { |
| 136 | + if let Some((did, param_did)) = def.as_const_arg() { |
| 137 | + self.thir_abstract_const_of_const_arg((did, param_did)) |
| 138 | + } else { |
| 139 | + self.thir_abstract_const(def.did) |
| 140 | + } |
| 141 | + } |
| 142 | +} |
| 143 | + |
| 144 | +#[instrument(skip(tcx, f), level = "debug")] |
| 145 | +pub fn walk_abstract_const<'tcx, R, F>( |
| 146 | + tcx: TyCtxt<'tcx>, |
| 147 | + ct: AbstractConst<'tcx>, |
| 148 | + mut f: F, |
| 149 | +) -> ControlFlow<R> |
| 150 | +where |
| 151 | + F: FnMut(AbstractConst<'tcx>) -> ControlFlow<R>, |
| 152 | +{ |
| 153 | + #[instrument(skip(tcx, f), level = "debug")] |
| 154 | + fn recurse<'tcx, R>( |
| 155 | + tcx: TyCtxt<'tcx>, |
| 156 | + ct: AbstractConst<'tcx>, |
| 157 | + f: &mut dyn FnMut(AbstractConst<'tcx>) -> ControlFlow<R>, |
| 158 | + ) -> ControlFlow<R> { |
| 159 | + f(ct)?; |
| 160 | + let root = ct.root(tcx); |
| 161 | + debug!(?root); |
| 162 | + match root { |
| 163 | + Node::Leaf(_) => ControlFlow::CONTINUE, |
| 164 | + Node::Binop(_, l, r) => { |
| 165 | + recurse(tcx, ct.subtree(l), f)?; |
| 166 | + recurse(tcx, ct.subtree(r), f) |
| 167 | + } |
| 168 | + Node::UnaryOp(_, v) => recurse(tcx, ct.subtree(v), f), |
| 169 | + Node::FunctionCall(func, args) => { |
| 170 | + recurse(tcx, ct.subtree(func), f)?; |
| 171 | + args.iter().try_for_each(|&arg| recurse(tcx, ct.subtree(arg), f)) |
| 172 | + } |
| 173 | + Node::Cast(_, operand, _) => recurse(tcx, ct.subtree(operand), f), |
| 174 | + } |
| 175 | + } |
| 176 | + |
| 177 | + recurse(tcx, ct, &mut f) |
| 178 | +} |
| 179 | + |
| 180 | +// We were unable to unify the abstract constant with |
| 181 | +// a constant found in the caller bounds, there are |
| 182 | +// now three possible cases here. |
| 183 | +#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord)] |
| 184 | +pub enum FailureKind { |
| 185 | + /// The abstract const still references an inference |
| 186 | + /// variable, in this case we return `TooGeneric`. |
| 187 | + MentionsInfer, |
| 188 | + /// The abstract const references a generic parameter, |
| 189 | + /// this means that we emit an error here. |
| 190 | + MentionsParam, |
| 191 | + /// The substs are concrete enough that we can simply |
| 192 | + /// try and evaluate the given constant. |
| 193 | + Concrete, |
| 194 | +} |
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