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Diffstat (limited to 'compiler/rustc_middle/src/ty/abstract_const.rs')
| -rw-r--r-- | compiler/rustc_middle/src/ty/abstract_const.rs | 194 |
1 files changed, 194 insertions, 0 deletions
diff --git a/compiler/rustc_middle/src/ty/abstract_const.rs b/compiler/rustc_middle/src/ty/abstract_const.rs new file mode 100644 index 000000000..bed809930 --- /dev/null +++ b/compiler/rustc_middle/src/ty/abstract_const.rs @@ -0,0 +1,194 @@ +//! A subset of a mir body used for const evaluatability checking. +use crate::mir; +use crate::ty::visit::TypeVisitable; +use crate::ty::{self, subst::Subst, DelaySpanBugEmitted, EarlyBinder, SubstsRef, Ty, TyCtxt}; +use rustc_errors::ErrorGuaranteed; +use rustc_hir::def_id::DefId; +use std::cmp; +use std::ops::ControlFlow; + +rustc_index::newtype_index! { + /// An index into an `AbstractConst`. + pub struct NodeId { + derive [HashStable] + DEBUG_FORMAT = "n{}", + } +} + +/// A tree representing an anonymous constant. +/// +/// This is only able to represent a subset of `MIR`, +/// and should not leak any information about desugarings. +#[derive(Debug, Clone, Copy)] +pub struct AbstractConst<'tcx> { + // FIXME: Consider adding something like `IndexSlice` + // and use this here. + inner: &'tcx [Node<'tcx>], + substs: SubstsRef<'tcx>, +} + +impl<'tcx> AbstractConst<'tcx> { + pub fn new( + tcx: TyCtxt<'tcx>, + uv: ty::Unevaluated<'tcx, ()>, + ) -> Result<Option<AbstractConst<'tcx>>, ErrorGuaranteed> { + let inner = tcx.thir_abstract_const_opt_const_arg(uv.def)?; + debug!("AbstractConst::new({:?}) = {:?}", uv, inner); + Ok(inner.map(|inner| AbstractConst { inner, substs: tcx.erase_regions(uv.substs) })) + } + + pub fn from_const( + tcx: TyCtxt<'tcx>, + ct: ty::Const<'tcx>, + ) -> Result<Option<AbstractConst<'tcx>>, ErrorGuaranteed> { + match ct.kind() { + ty::ConstKind::Unevaluated(uv) => AbstractConst::new(tcx, uv.shrink()), + ty::ConstKind::Error(DelaySpanBugEmitted { reported, .. }) => Err(reported), + _ => Ok(None), + } + } + + #[inline] + pub fn subtree(self, node: NodeId) -> AbstractConst<'tcx> { + AbstractConst { inner: &self.inner[..=node.index()], substs: self.substs } + } + + #[inline] + pub fn root(self, tcx: TyCtxt<'tcx>) -> Node<'tcx> { + let node = self.inner.last().copied().unwrap(); + match node { + Node::Leaf(leaf) => Node::Leaf(EarlyBinder(leaf).subst(tcx, self.substs)), + Node::Cast(kind, operand, ty) => { + Node::Cast(kind, operand, EarlyBinder(ty).subst(tcx, self.substs)) + } + // Don't perform substitution on the following as they can't directly contain generic params + Node::Binop(_, _, _) | Node::UnaryOp(_, _) | Node::FunctionCall(_, _) => node, + } + } + + pub fn unify_failure_kind(self, tcx: TyCtxt<'tcx>) -> FailureKind { + let mut failure_kind = FailureKind::Concrete; + walk_abstract_const::<!, _>(tcx, self, |node| { + match node.root(tcx) { + Node::Leaf(leaf) => { + if leaf.has_infer_types_or_consts() { + failure_kind = FailureKind::MentionsInfer; + } else if leaf.has_param_types_or_consts() { + failure_kind = cmp::min(failure_kind, FailureKind::MentionsParam); + } + } + Node::Cast(_, _, ty) => { + if ty.has_infer_types_or_consts() { + failure_kind = FailureKind::MentionsInfer; + } else if ty.has_param_types_or_consts() { + failure_kind = cmp::min(failure_kind, FailureKind::MentionsParam); + } + } + Node::Binop(_, _, _) | Node::UnaryOp(_, _) | Node::FunctionCall(_, _) => {} + } + ControlFlow::CONTINUE + }); + failure_kind + } +} + +#[derive(Debug, Clone, Copy, PartialEq, Eq, HashStable, TyEncodable, TyDecodable)] +pub enum CastKind { + /// thir::ExprKind::As + As, + /// thir::ExprKind::Use + Use, +} + +/// A node of an `AbstractConst`. +#[derive(Debug, Clone, Copy, PartialEq, Eq, HashStable, TyEncodable, TyDecodable)] +pub enum Node<'tcx> { + Leaf(ty::Const<'tcx>), + Binop(mir::BinOp, NodeId, NodeId), + UnaryOp(mir::UnOp, NodeId), + FunctionCall(NodeId, &'tcx [NodeId]), + Cast(CastKind, NodeId, Ty<'tcx>), +} + +#[derive(Debug, Copy, Clone, PartialEq, Eq, HashStable, TyEncodable, TyDecodable)] +pub enum NotConstEvaluatable { + Error(ErrorGuaranteed), + MentionsInfer, + MentionsParam, +} + +impl From<ErrorGuaranteed> for NotConstEvaluatable { + fn from(e: ErrorGuaranteed) -> NotConstEvaluatable { + NotConstEvaluatable::Error(e) + } +} + +TrivialTypeTraversalAndLiftImpls! { + NotConstEvaluatable, +} + +impl<'tcx> TyCtxt<'tcx> { + #[inline] + pub fn thir_abstract_const_opt_const_arg( + self, + def: ty::WithOptConstParam<DefId>, + ) -> Result<Option<&'tcx [Node<'tcx>]>, ErrorGuaranteed> { + if let Some((did, param_did)) = def.as_const_arg() { + self.thir_abstract_const_of_const_arg((did, param_did)) + } else { + self.thir_abstract_const(def.did) + } + } +} + +#[instrument(skip(tcx, f), level = "debug")] +pub fn walk_abstract_const<'tcx, R, F>( + tcx: TyCtxt<'tcx>, + ct: AbstractConst<'tcx>, + mut f: F, +) -> ControlFlow<R> +where + F: FnMut(AbstractConst<'tcx>) -> ControlFlow<R>, +{ + #[instrument(skip(tcx, f), level = "debug")] + fn recurse<'tcx, R>( + tcx: TyCtxt<'tcx>, + ct: AbstractConst<'tcx>, + f: &mut dyn FnMut(AbstractConst<'tcx>) -> ControlFlow<R>, + ) -> ControlFlow<R> { + f(ct)?; + let root = ct.root(tcx); + debug!(?root); + match root { + Node::Leaf(_) => ControlFlow::CONTINUE, + Node::Binop(_, l, r) => { + recurse(tcx, ct.subtree(l), f)?; + recurse(tcx, ct.subtree(r), f) + } + Node::UnaryOp(_, v) => recurse(tcx, ct.subtree(v), f), + Node::FunctionCall(func, args) => { + recurse(tcx, ct.subtree(func), f)?; + args.iter().try_for_each(|&arg| recurse(tcx, ct.subtree(arg), f)) + } + Node::Cast(_, operand, _) => recurse(tcx, ct.subtree(operand), f), + } + } + + recurse(tcx, ct, &mut f) +} + +// We were unable to unify the abstract constant with +// a constant found in the caller bounds, there are +// now three possible cases here. +#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord)] +pub enum FailureKind { + /// The abstract const still references an inference + /// variable, in this case we return `TooGeneric`. + MentionsInfer, + /// The abstract const references a generic parameter, + /// this means that we emit an error here. + MentionsParam, + /// The substs are concrete enough that we can simply + /// try and evaluate the given constant. + Concrete, +} |