From 20431706a863f92cb37dc512fef6e48d192aaf2c Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Wed, 17 Apr 2024 14:11:38 +0200 Subject: Merging upstream version 1.66.0+dfsg1. Signed-off-by: Daniel Baumann --- compiler/rustc_middle/src/ty/inhabitedness/mod.rs | 258 ++++++++++------------ 1 file changed, 111 insertions(+), 147 deletions(-) (limited to 'compiler/rustc_middle/src/ty/inhabitedness/mod.rs') diff --git a/compiler/rustc_middle/src/ty/inhabitedness/mod.rs b/compiler/rustc_middle/src/ty/inhabitedness/mod.rs index aaa66deb2..279a728ea 100644 --- a/compiler/rustc_middle/src/ty/inhabitedness/mod.rs +++ b/compiler/rustc_middle/src/ty/inhabitedness/mod.rs @@ -1,57 +1,60 @@ -pub use self::def_id_forest::DefIdForest; +//! This module contains logic for determining whether a type is inhabited or +//! uninhabited. The [`InhabitedPredicate`] type captures the minimum +//! information needed to determine whether a type is inhabited given a +//! `ParamEnv` and module ID. +//! +//! # Example +//! ```rust +//! enum Void {} +//! mod a { +//! pub mod b { +//! pub struct SecretlyUninhabited { +//! _priv: !, +//! } +//! } +//! } +//! +//! mod c { +//! pub struct AlsoSecretlyUninhabited { +//! _priv: Void, +//! } +//! mod d { +//! } +//! } +//! +//! struct Foo { +//! x: a::b::SecretlyUninhabited, +//! y: c::AlsoSecretlyUninhabited, +//! } +//! ``` +//! In this code, the type `Foo` will only be visibly uninhabited inside the +//! modules `b`, `c` and `d`. Calling `uninhabited_predicate` on `Foo` will +//! return `NotInModule(b) AND NotInModule(c)`. +//! +//! We need this information for pattern-matching on `Foo` or types that contain +//! `Foo`. +//! +//! # Example +//! ```rust +//! let foo_result: Result = ... ; +//! let Ok(t) = foo_result; +//! ``` +//! This code should only compile in modules where the uninhabitedness of `Foo` +//! is visible. -use crate::ty; use crate::ty::context::TyCtxt; -use crate::ty::{AdtDef, FieldDef, Ty, VariantDef}; -use crate::ty::{AdtKind, Visibility}; -use crate::ty::{DefId, SubstsRef}; +use crate::ty::{self, DefId, Ty, VariantDef, Visibility}; use rustc_type_ir::sty::TyKind::*; -mod def_id_forest; +pub mod inhabited_predicate; -// The methods in this module calculate `DefIdForest`s of modules in which an -// `AdtDef`/`VariantDef`/`FieldDef` is visibly uninhabited. -// -// # Example -// ```rust -// enum Void {} -// mod a { -// pub mod b { -// pub struct SecretlyUninhabited { -// _priv: !, -// } -// } -// } -// -// mod c { -// pub struct AlsoSecretlyUninhabited { -// _priv: Void, -// } -// mod d { -// } -// } -// -// struct Foo { -// x: a::b::SecretlyUninhabited, -// y: c::AlsoSecretlyUninhabited, -// } -// ``` -// In this code, the type `Foo` will only be visibly uninhabited inside the -// modules `b`, `c` and `d`. Calling `uninhabited_from` on `Foo` or its `AdtDef` will -// return the forest of modules {`b`, `c`->`d`} (represented in a `DefIdForest` by the -// set {`b`, `c`}). -// -// We need this information for pattern-matching on `Foo` or types that contain -// `Foo`. -// -// # Example -// ```rust -// let foo_result: Result = ... ; -// let Ok(t) = foo_result; -// ``` -// This code should only compile in modules where the uninhabitedness of `Foo` is -// visible. +pub use inhabited_predicate::InhabitedPredicate; + +pub(crate) fn provide(providers: &mut ty::query::Providers) { + *providers = + ty::query::Providers { inhabited_predicate_adt, inhabited_predicate_type, ..*providers }; +} impl<'tcx> TyCtxt<'tcx> { /// Checks whether a type is visibly uninhabited from a particular module. @@ -100,131 +103,92 @@ impl<'tcx> TyCtxt<'tcx> { ty: Ty<'tcx>, param_env: ty::ParamEnv<'tcx>, ) -> bool { - // To check whether this type is uninhabited at all (not just from the - // given node), you could check whether the forest is empty. - // ``` - // forest.is_empty() - // ``` - ty.uninhabited_from(self, param_env).contains(self, module) + !ty.inhabited_predicate(self).apply(self, param_env, module) } } -impl<'tcx> AdtDef<'tcx> { - /// Calculates the forest of `DefId`s from which this ADT is visibly uninhabited. - fn uninhabited_from( - self, - tcx: TyCtxt<'tcx>, - substs: SubstsRef<'tcx>, - param_env: ty::ParamEnv<'tcx>, - ) -> DefIdForest<'tcx> { - // Non-exhaustive ADTs from other crates are always considered inhabited. - if self.is_variant_list_non_exhaustive() && !self.did().is_local() { - DefIdForest::empty() - } else { - DefIdForest::intersection( - tcx, - self.variants() - .iter() - .map(|v| v.uninhabited_from(tcx, substs, self.adt_kind(), param_env)), - ) +/// Returns an `InhabitedPredicate` that is generic over type parameters and +/// requires calling [`InhabitedPredicate::subst`] +fn inhabited_predicate_adt(tcx: TyCtxt<'_>, def_id: DefId) -> InhabitedPredicate<'_> { + if let Some(def_id) = def_id.as_local() { + if matches!(tcx.representability(def_id), ty::Representability::Infinite) { + return InhabitedPredicate::True; } } + let adt = tcx.adt_def(def_id); + InhabitedPredicate::any( + tcx, + adt.variants().iter().map(|variant| variant.inhabited_predicate(tcx, adt)), + ) } impl<'tcx> VariantDef { /// Calculates the forest of `DefId`s from which this variant is visibly uninhabited. - pub fn uninhabited_from( + pub fn inhabited_predicate( &self, tcx: TyCtxt<'tcx>, - substs: SubstsRef<'tcx>, - adt_kind: AdtKind, - param_env: ty::ParamEnv<'tcx>, - ) -> DefIdForest<'tcx> { - let is_enum = match adt_kind { - // For now, `union`s are never considered uninhabited. - // The precise semantics of inhabitedness with respect to unions is currently undecided. - AdtKind::Union => return DefIdForest::empty(), - AdtKind::Enum => true, - AdtKind::Struct => false, - }; - // Non-exhaustive variants from other crates are always considered inhabited. + adt: ty::AdtDef<'_>, + ) -> InhabitedPredicate<'tcx> { + debug_assert!(!adt.is_union()); if self.is_field_list_non_exhaustive() && !self.def_id.is_local() { - DefIdForest::empty() - } else { - DefIdForest::union( - tcx, - self.fields.iter().map(|f| f.uninhabited_from(tcx, substs, is_enum, param_env)), - ) + // Non-exhaustive variants from other crates are always considered inhabited. + return InhabitedPredicate::True; } - } -} - -impl<'tcx> FieldDef { - /// Calculates the forest of `DefId`s from which this field is visibly uninhabited. - fn uninhabited_from( - &self, - tcx: TyCtxt<'tcx>, - substs: SubstsRef<'tcx>, - is_enum: bool, - param_env: ty::ParamEnv<'tcx>, - ) -> DefIdForest<'tcx> { - let data_uninhabitedness = move || self.ty(tcx, substs).uninhabited_from(tcx, param_env); - if is_enum { - data_uninhabitedness() - } else { - match self.vis { - Visibility::Restricted(from) => { - let forest = DefIdForest::from_id(from); - let iter = Some(forest).into_iter().chain(Some(data_uninhabitedness())); - DefIdForest::intersection(tcx, iter) + InhabitedPredicate::all( + tcx, + self.fields.iter().map(|field| { + let pred = tcx.type_of(field.did).inhabited_predicate(tcx); + if adt.is_enum() { + return pred; } - Visibility::Public => data_uninhabitedness(), - } - } + match field.vis { + Visibility::Public => pred, + Visibility::Restricted(from) => { + pred.or(tcx, InhabitedPredicate::NotInModule(from)) + } + } + }), + ) } } impl<'tcx> Ty<'tcx> { - /// Calculates the forest of `DefId`s from which this type is visibly uninhabited. - fn uninhabited_from( - self, - tcx: TyCtxt<'tcx>, - param_env: ty::ParamEnv<'tcx>, - ) -> DefIdForest<'tcx> { - tcx.type_uninhabited_from(param_env.and(self)) + pub fn inhabited_predicate(self, tcx: TyCtxt<'tcx>) -> InhabitedPredicate<'tcx> { + match self.kind() { + // For now, union`s are always considered inhabited + Adt(adt, _) if adt.is_union() => InhabitedPredicate::True, + // Non-exhaustive ADTs from other crates are always considered inhabited + Adt(adt, _) if adt.is_variant_list_non_exhaustive() && !adt.did().is_local() => { + InhabitedPredicate::True + } + Never => InhabitedPredicate::False, + Param(_) | Projection(_) => InhabitedPredicate::GenericType(self), + Tuple(tys) if tys.is_empty() => InhabitedPredicate::True, + // use a query for more complex cases + Adt(..) | Array(..) | Tuple(_) => tcx.inhabited_predicate_type(self), + // references and other types are inhabited + _ => InhabitedPredicate::True, + } } } -// Query provider for `type_uninhabited_from`. -pub(crate) fn type_uninhabited_from<'tcx>( - tcx: TyCtxt<'tcx>, - key: ty::ParamEnvAnd<'tcx, Ty<'tcx>>, -) -> DefIdForest<'tcx> { - let ty = key.value; - let param_env = key.param_env; +/// N.B. this query should only be called through `Ty::inhabited_predicate` +fn inhabited_predicate_type<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> InhabitedPredicate<'tcx> { match *ty.kind() { - Adt(def, substs) => def.uninhabited_from(tcx, substs, param_env), + Adt(adt, substs) => tcx.inhabited_predicate_adt(adt.did()).subst(tcx, substs), - Never => DefIdForest::full(), - - Tuple(ref tys) => { - DefIdForest::union(tcx, tys.iter().map(|ty| ty.uninhabited_from(tcx, param_env))) + Tuple(tys) => { + InhabitedPredicate::all(tcx, tys.iter().map(|ty| ty.inhabited_predicate(tcx))) } - Array(ty, len) => match len.try_eval_usize(tcx, param_env) { - Some(0) | None => DefIdForest::empty(), - // If the array is definitely non-empty, it's uninhabited if - // the type of its elements is uninhabited. - Some(1..) => ty.uninhabited_from(tcx, param_env), + // If we can evaluate the array length before having a `ParamEnv`, then + // we can simplify the predicate. This is an optimization. + Array(ty, len) => match len.kind().try_to_machine_usize(tcx) { + Some(0) => InhabitedPredicate::True, + Some(1..) => ty.inhabited_predicate(tcx), + None => ty.inhabited_predicate(tcx).or(tcx, InhabitedPredicate::ConstIsZero(len)), }, - // References to uninitialised memory are valid for any type, including - // uninhabited types, in unsafe code, so we treat all references as - // inhabited. - // The precise semantics of inhabitedness with respect to references is currently - // undecided. - Ref(..) => DefIdForest::empty(), - - _ => DefIdForest::empty(), + _ => bug!("unexpected TyKind, use `Ty::inhabited_predicate`"), } } -- cgit v1.2.3