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|
//! 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,
}
|
