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use smallvec::SmallVec;
use crate::ty::context::TyCtxt;
use crate::ty::{self, DefId, ParamEnv, Ty};
/// Represents whether some type is inhabited in a given context.
/// Examples of uninhabited types are `!`, `enum Void {}`, or a struct
/// containing either of those types.
/// A type's inhabitedness may depend on the `ParamEnv` as well as what types
/// are visible in the current module.
#[derive(Clone, Copy, Debug, PartialEq, HashStable)]
pub enum InhabitedPredicate<'tcx> {
/// Inhabited
True,
/// Uninhabited
False,
/// Uninhabited when a const value is non-zero. This occurs when there is an
/// array of uninhabited items, but the array is inhabited if it is empty.
ConstIsZero(ty::Const<'tcx>),
/// Uninhabited if within a certain module. This occurs when an uninhabited
/// type has restricted visibility.
NotInModule(DefId),
/// Inhabited if some generic type is inhabited.
/// These are replaced by calling [`Self::instantiate`].
GenericType(Ty<'tcx>),
/// A AND B
And(&'tcx [InhabitedPredicate<'tcx>; 2]),
/// A OR B
Or(&'tcx [InhabitedPredicate<'tcx>; 2]),
}
impl<'tcx> InhabitedPredicate<'tcx> {
/// Returns true if the corresponding type is inhabited in the given
/// `ParamEnv` and module
pub fn apply(self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>, module_def_id: DefId) -> bool {
let Ok(result) = self.apply_inner::<!>(tcx, param_env, &mut Default::default(), &|id| {
Ok(tcx.is_descendant_of(module_def_id, id))
});
result
}
/// Same as `apply`, but returns `None` if self contains a module predicate
pub fn apply_any_module(self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>) -> Option<bool> {
self.apply_inner(tcx, param_env, &mut Default::default(), &|_| Err(())).ok()
}
/// Same as `apply`, but `NotInModule(_)` predicates yield `false`. That is,
/// privately uninhabited types are considered always uninhabited.
pub fn apply_ignore_module(self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>) -> bool {
let Ok(result) =
self.apply_inner::<!>(tcx, param_env, &mut Default::default(), &|_| Ok(true));
result
}
#[instrument(level = "debug", skip(tcx, param_env, in_module), ret)]
fn apply_inner<E: std::fmt::Debug>(
self,
tcx: TyCtxt<'tcx>,
param_env: ParamEnv<'tcx>,
eval_stack: &mut SmallVec<[Ty<'tcx>; 1]>, // for cycle detection
in_module: &impl Fn(DefId) -> Result<bool, E>,
) -> Result<bool, E> {
match self {
Self::False => Ok(false),
Self::True => Ok(true),
Self::ConstIsZero(const_) => match const_.try_eval_target_usize(tcx, param_env) {
None | Some(0) => Ok(true),
Some(1..) => Ok(false),
},
Self::NotInModule(id) => in_module(id).map(|in_mod| !in_mod),
// `t` may be a projection, for which `inhabited_predicate` returns a `GenericType`. As
// we have a param_env available, we can do better.
Self::GenericType(t) => {
let normalized_pred = tcx
.try_normalize_erasing_regions(param_env, t)
.map_or(self, |t| t.inhabited_predicate(tcx));
match normalized_pred {
// We don't have more information than we started with, so consider inhabited.
Self::GenericType(_) => Ok(true),
pred => {
// A type which is cyclic when monomorphized can happen here since the
// layout error would only trigger later. See e.g. `tests/ui/sized/recursive-type-2.rs`.
if eval_stack.contains(&t) {
return Ok(true); // Recover; this will error later.
}
eval_stack.push(t);
let ret = pred.apply_inner(tcx, param_env, eval_stack, in_module);
eval_stack.pop();
ret
}
}
}
Self::And([a, b]) => {
try_and(a, b, |x| x.apply_inner(tcx, param_env, eval_stack, in_module))
}
Self::Or([a, b]) => {
try_or(a, b, |x| x.apply_inner(tcx, param_env, eval_stack, in_module))
}
}
}
pub fn and(self, tcx: TyCtxt<'tcx>, other: Self) -> Self {
self.reduce_and(tcx, other).unwrap_or_else(|| Self::And(tcx.arena.alloc([self, other])))
}
pub fn or(self, tcx: TyCtxt<'tcx>, other: Self) -> Self {
self.reduce_or(tcx, other).unwrap_or_else(|| Self::Or(tcx.arena.alloc([self, other])))
}
pub fn all(tcx: TyCtxt<'tcx>, iter: impl IntoIterator<Item = Self>) -> Self {
let mut result = Self::True;
for pred in iter {
if matches!(pred, Self::False) {
return Self::False;
}
result = result.and(tcx, pred);
}
result
}
pub fn any(tcx: TyCtxt<'tcx>, iter: impl IntoIterator<Item = Self>) -> Self {
let mut result = Self::False;
for pred in iter {
if matches!(pred, Self::True) {
return Self::True;
}
result = result.or(tcx, pred);
}
result
}
fn reduce_and(self, tcx: TyCtxt<'tcx>, other: Self) -> Option<Self> {
match (self, other) {
(Self::True, a) | (a, Self::True) => Some(a),
(Self::False, _) | (_, Self::False) => Some(Self::False),
(Self::ConstIsZero(a), Self::ConstIsZero(b)) if a == b => Some(Self::ConstIsZero(a)),
(Self::NotInModule(a), Self::NotInModule(b)) if a == b => Some(Self::NotInModule(a)),
(Self::NotInModule(a), Self::NotInModule(b)) if tcx.is_descendant_of(a, b) => {
Some(Self::NotInModule(b))
}
(Self::NotInModule(a), Self::NotInModule(b)) if tcx.is_descendant_of(b, a) => {
Some(Self::NotInModule(a))
}
(Self::GenericType(a), Self::GenericType(b)) if a == b => Some(Self::GenericType(a)),
(Self::And(&[a, b]), c) | (c, Self::And(&[a, b])) => {
if let Some(ac) = a.reduce_and(tcx, c) {
Some(ac.and(tcx, b))
} else if let Some(bc) = b.reduce_and(tcx, c) {
Some(Self::And(tcx.arena.alloc([a, bc])))
} else {
None
}
}
_ => None,
}
}
fn reduce_or(self, tcx: TyCtxt<'tcx>, other: Self) -> Option<Self> {
match (self, other) {
(Self::True, _) | (_, Self::True) => Some(Self::True),
(Self::False, a) | (a, Self::False) => Some(a),
(Self::ConstIsZero(a), Self::ConstIsZero(b)) if a == b => Some(Self::ConstIsZero(a)),
(Self::NotInModule(a), Self::NotInModule(b)) if a == b => Some(Self::NotInModule(a)),
(Self::NotInModule(a), Self::NotInModule(b)) if tcx.is_descendant_of(a, b) => {
Some(Self::NotInModule(a))
}
(Self::NotInModule(a), Self::NotInModule(b)) if tcx.is_descendant_of(b, a) => {
Some(Self::NotInModule(b))
}
(Self::GenericType(a), Self::GenericType(b)) if a == b => Some(Self::GenericType(a)),
(Self::Or(&[a, b]), c) | (c, Self::Or(&[a, b])) => {
if let Some(ac) = a.reduce_or(tcx, c) {
Some(ac.or(tcx, b))
} else if let Some(bc) = b.reduce_or(tcx, c) {
Some(Self::Or(tcx.arena.alloc([a, bc])))
} else {
None
}
}
_ => None,
}
}
/// Replaces generic types with its corresponding predicate
pub fn instantiate(self, tcx: TyCtxt<'tcx>, args: ty::GenericArgsRef<'tcx>) -> Self {
self.instantiate_opt(tcx, args).unwrap_or(self)
}
fn instantiate_opt(self, tcx: TyCtxt<'tcx>, args: ty::GenericArgsRef<'tcx>) -> Option<Self> {
match self {
Self::ConstIsZero(c) => {
let c = ty::EarlyBinder::bind(c).instantiate(tcx, args);
let pred = match c.try_to_target_usize(tcx) {
Some(0) => Self::True,
Some(1..) => Self::False,
None => Self::ConstIsZero(c),
};
Some(pred)
}
Self::GenericType(t) => {
Some(ty::EarlyBinder::bind(t).instantiate(tcx, args).inhabited_predicate(tcx))
}
Self::And(&[a, b]) => match a.instantiate_opt(tcx, args) {
None => b.instantiate_opt(tcx, args).map(|b| a.and(tcx, b)),
Some(InhabitedPredicate::False) => Some(InhabitedPredicate::False),
Some(a) => Some(a.and(tcx, b.instantiate_opt(tcx, args).unwrap_or(b))),
},
Self::Or(&[a, b]) => match a.instantiate_opt(tcx, args) {
None => b.instantiate_opt(tcx, args).map(|b| a.or(tcx, b)),
Some(InhabitedPredicate::True) => Some(InhabitedPredicate::True),
Some(a) => Some(a.or(tcx, b.instantiate_opt(tcx, args).unwrap_or(b))),
},
_ => None,
}
}
}
// this is basically like `f(a)? && f(b)?` but different in the case of
// `Ok(false) && Err(_) -> Ok(false)`
fn try_and<T, E>(a: T, b: T, mut f: impl FnMut(T) -> Result<bool, E>) -> Result<bool, E> {
let a = f(a);
if matches!(a, Ok(false)) {
return Ok(false);
}
match (a, f(b)) {
(_, Ok(false)) | (Ok(false), _) => Ok(false),
(Ok(true), Ok(true)) => Ok(true),
(Err(e), _) | (_, Err(e)) => Err(e),
}
}
fn try_or<T, E>(a: T, b: T, mut f: impl FnMut(T) -> Result<bool, E>) -> Result<bool, E> {
let a = f(a);
if matches!(a, Ok(true)) {
return Ok(true);
}
match (a, f(b)) {
(_, Ok(true)) | (Ok(true), _) => Ok(true),
(Ok(false), Ok(false)) => Ok(false),
(Err(e), _) | (_, Err(e)) => Err(e),
}
}
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