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Auto merge of rust-lang#13167 - iDawer:exhaustive_patterns, r=Veykril
feat: Implement `feature(exhaustive_patterns)` from unstable Rust Closes rust-lang#12753 Recognize Rust's unstable `#![feature(exhaustive_patterns)]` (RFC 1872). Allow omitting visibly uninhabited variants from `match` expressions when the feature is on. This adjusts match checking to the current implementation of the postponed RFC 1872 in rustc.
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,173 @@ | ||
| //! Type inhabitedness logic. | ||
| use std::ops::ControlFlow::{self, Break, Continue}; | ||
|
|
||
| use chalk_ir::{ | ||
| visit::{TypeSuperVisitable, TypeVisitable, TypeVisitor}, | ||
| DebruijnIndex, | ||
| }; | ||
| use hir_def::{ | ||
| adt::VariantData, attr::Attrs, type_ref::ConstScalar, visibility::Visibility, AdtId, | ||
| EnumVariantId, HasModule, Lookup, ModuleId, VariantId, | ||
| }; | ||
|
|
||
| use crate::{ | ||
| db::HirDatabase, Binders, ConcreteConst, Const, ConstValue, Interner, Substitution, Ty, TyKind, | ||
| }; | ||
|
|
||
| /// Checks whether a type is visibly uninhabited from a particular module. | ||
| pub(crate) fn is_ty_uninhabited_from(ty: &Ty, target_mod: ModuleId, db: &dyn HirDatabase) -> bool { | ||
| let mut uninhabited_from = UninhabitedFrom { target_mod, db }; | ||
| let inhabitedness = ty.visit_with(&mut uninhabited_from, DebruijnIndex::INNERMOST); | ||
| inhabitedness == BREAK_VISIBLY_UNINHABITED | ||
| } | ||
|
|
||
| /// Checks whether a variant is visibly uninhabited from a particular module. | ||
| pub(crate) fn is_enum_variant_uninhabited_from( | ||
| variant: EnumVariantId, | ||
| subst: &Substitution, | ||
| target_mod: ModuleId, | ||
| db: &dyn HirDatabase, | ||
| ) -> bool { | ||
| let enum_data = db.enum_data(variant.parent); | ||
| let vars_attrs = db.variants_attrs(variant.parent); | ||
| let is_local = variant.parent.lookup(db.upcast()).container.krate() == target_mod.krate(); | ||
|
|
||
| let mut uninhabited_from = UninhabitedFrom { target_mod, db }; | ||
| let inhabitedness = uninhabited_from.visit_variant( | ||
| variant.into(), | ||
| &enum_data.variants[variant.local_id].variant_data, | ||
| subst, | ||
| &vars_attrs[variant.local_id], | ||
| is_local, | ||
| ); | ||
| inhabitedness == BREAK_VISIBLY_UNINHABITED | ||
| } | ||
|
|
||
| struct UninhabitedFrom<'a> { | ||
| target_mod: ModuleId, | ||
| db: &'a dyn HirDatabase, | ||
| } | ||
|
|
||
| const CONTINUE_OPAQUELY_INHABITED: ControlFlow<VisiblyUninhabited> = Continue(()); | ||
| const BREAK_VISIBLY_UNINHABITED: ControlFlow<VisiblyUninhabited> = Break(VisiblyUninhabited); | ||
| #[derive(PartialEq, Eq)] | ||
| struct VisiblyUninhabited; | ||
|
|
||
| impl TypeVisitor<Interner> for UninhabitedFrom<'_> { | ||
| type BreakTy = VisiblyUninhabited; | ||
|
|
||
| fn as_dyn(&mut self) -> &mut dyn TypeVisitor<Interner, BreakTy = VisiblyUninhabited> { | ||
| self | ||
| } | ||
|
|
||
| fn visit_ty( | ||
| &mut self, | ||
| ty: &Ty, | ||
| outer_binder: DebruijnIndex, | ||
| ) -> ControlFlow<VisiblyUninhabited> { | ||
| match ty.kind(Interner) { | ||
| TyKind::Adt(adt, subst) => self.visit_adt(adt.0, subst), | ||
| TyKind::Never => BREAK_VISIBLY_UNINHABITED, | ||
| TyKind::Tuple(..) => ty.super_visit_with(self, outer_binder), | ||
| TyKind::Array(item_ty, len) => match try_usize_const(len) { | ||
| Some(0) | None => CONTINUE_OPAQUELY_INHABITED, | ||
| Some(1..) => item_ty.super_visit_with(self, outer_binder), | ||
| }, | ||
|
|
||
| TyKind::Ref(..) | _ => CONTINUE_OPAQUELY_INHABITED, | ||
| } | ||
| } | ||
|
|
||
| fn interner(&self) -> Interner { | ||
| Interner | ||
| } | ||
| } | ||
|
|
||
| impl UninhabitedFrom<'_> { | ||
| fn visit_adt(&mut self, adt: AdtId, subst: &Substitution) -> ControlFlow<VisiblyUninhabited> { | ||
| let attrs = self.db.attrs(adt.into()); | ||
| let adt_non_exhaustive = attrs.by_key("non_exhaustive").exists(); | ||
| let is_local = adt.module(self.db.upcast()).krate() == self.target_mod.krate(); | ||
| if adt_non_exhaustive && !is_local { | ||
| return CONTINUE_OPAQUELY_INHABITED; | ||
| } | ||
|
|
||
| // An ADT is uninhabited iff all its variants uninhabited. | ||
| match adt { | ||
| // rustc: For now, `union`s are never considered uninhabited. | ||
| AdtId::UnionId(_) => CONTINUE_OPAQUELY_INHABITED, | ||
| AdtId::StructId(s) => { | ||
| let struct_data = self.db.struct_data(s); | ||
| self.visit_variant(s.into(), &struct_data.variant_data, subst, &attrs, is_local) | ||
| } | ||
| AdtId::EnumId(e) => { | ||
| let vars_attrs = self.db.variants_attrs(e); | ||
| let enum_data = self.db.enum_data(e); | ||
|
|
||
| for (local_id, enum_var) in enum_data.variants.iter() { | ||
| let variant_inhabitedness = self.visit_variant( | ||
| EnumVariantId { parent: e, local_id }.into(), | ||
| &enum_var.variant_data, | ||
| subst, | ||
| &vars_attrs[local_id], | ||
| is_local, | ||
| ); | ||
| match variant_inhabitedness { | ||
| Break(VisiblyUninhabited) => continue, | ||
| Continue(()) => return CONTINUE_OPAQUELY_INHABITED, | ||
| } | ||
| } | ||
| BREAK_VISIBLY_UNINHABITED | ||
| } | ||
| } | ||
| } | ||
|
|
||
| fn visit_variant( | ||
| &mut self, | ||
| variant: VariantId, | ||
| variant_data: &VariantData, | ||
| subst: &Substitution, | ||
| attrs: &Attrs, | ||
| is_local: bool, | ||
| ) -> ControlFlow<VisiblyUninhabited> { | ||
| let non_exhaustive_field_list = attrs.by_key("non_exhaustive").exists(); | ||
| if non_exhaustive_field_list && !is_local { | ||
| return CONTINUE_OPAQUELY_INHABITED; | ||
| } | ||
|
|
||
| let is_enum = matches!(variant, VariantId::EnumVariantId(..)); | ||
| let field_tys = self.db.field_types(variant); | ||
| let field_vis = self.db.field_visibilities(variant); | ||
|
|
||
| for (fid, _) in variant_data.fields().iter() { | ||
| self.visit_field(field_vis[fid], &field_tys[fid], subst, is_enum)?; | ||
| } | ||
| CONTINUE_OPAQUELY_INHABITED | ||
| } | ||
|
|
||
| fn visit_field( | ||
| &mut self, | ||
| vis: Visibility, | ||
| ty: &Binders<Ty>, | ||
| subst: &Substitution, | ||
| is_enum: bool, | ||
| ) -> ControlFlow<VisiblyUninhabited> { | ||
| if is_enum || vis.is_visible_from(self.db.upcast(), self.target_mod) { | ||
| let ty = ty.clone().substitute(Interner, subst); | ||
| ty.visit_with(self, DebruijnIndex::INNERMOST) | ||
| } else { | ||
| CONTINUE_OPAQUELY_INHABITED | ||
| } | ||
| } | ||
| } | ||
|
|
||
| fn try_usize_const(c: &Const) -> Option<u128> { | ||
| let data = &c.data(Interner); | ||
| if data.ty.kind(Interner) != &TyKind::Scalar(chalk_ir::Scalar::Uint(chalk_ir::UintTy::Usize)) { | ||
| return None; | ||
| } | ||
| match data.value { | ||
| ConstValue::Concrete(ConcreteConst { interned: ConstScalar::UInt(value) }) => Some(value), | ||
| _ => None, | ||
| } | ||
| } |
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