Auto merge of #53721 - arielb1:exhaustively-unpun, r=nikomatsakis

fix `is_non_exhaustive` confusion between structs and enums

Structs and enums can both be non-exhaustive, with a very different
meaning. This PR splits `is_non_exhaustive` to 2 separate functions - 1
for structs, and another for enums, and fixes the places that got the
usage confused.

Fixes #53549.

r? @eddyb

src/librustc/ich/impls_ty.rs

@@ -344,13 +344,13 @@ impl<'a> HashStable<StableHashingContext<'a>> for ty::AdtFlags {
     }
 }
 
-impl_stable_hash_for!(struct ty::VariantDef {
-    did,
-    name,
-    discr,
-    fields,
-    ctor_kind
-});
+impl<'a> HashStable<StableHashingContext<'a>> for ty::VariantFlags {
+    fn hash_stable<W: StableHasherResult>(&self,
+                                          _: &mut StableHashingContext<'a>,
+                                          hasher: &mut StableHasher<W>) {
+        std_hash::Hash::hash(self, hasher);
+    }
+}
 
 impl_stable_hash_for!(enum ty::VariantDiscr {
     Explicit(def_id),

src/librustc/ty/mod.rs

@@ -1692,12 +1692,17 @@ bitflags! {
         const IS_FUNDAMENTAL      = 1 << 2;
         const IS_UNION            = 1 << 3;
         const IS_BOX              = 1 << 4;
-        /// Indicates whether this abstract data type will be expanded on in future (new
-        /// fields/variants) and as such, whether downstream crates must match exhaustively on the
-        /// fields/variants of this data type.
-        ///
-        /// See RFC 2008 (</~https://github.com/rust-lang/rfcs/pull/2008>).
-        const IS_NON_EXHAUSTIVE   = 1 << 5;
+        /// Indicates whether the variant list of this ADT is `#[non_exhaustive]`.
+        /// (i.e., this flag is never set unless this ADT is an enum).
+        const IS_VARIANT_LIST_NON_EXHAUSTIVE   = 1 << 5;
+    }
+}
+
+bitflags! {
+    pub struct VariantFlags: u32 {
+        const NO_VARIANT_FLAGS        = 0;
+        /// Indicates whether the field list of this variant is `#[non_exhaustive]`.
+        const IS_FIELD_LIST_NON_EXHAUSTIVE = 1 << 0;
     }
 }
 
@@ -1710,8 +1715,56 @@ pub struct VariantDef {
     pub discr: VariantDiscr,
     pub fields: Vec<FieldDef>,
     pub ctor_kind: CtorKind,
+    flags: VariantFlags,
 }
 
+impl<'a, 'gcx, 'tcx> VariantDef {
+    /// Create a new `VariantDef`.
+    ///
+    /// - `did` is the DefId used for the variant - for tuple-structs, it is the constructor DefId,
+    /// and for everything else, it is the variant DefId.
+    /// - `attribute_def_id` is the DefId that has the variant's attributes.
+    pub fn new(tcx: TyCtxt<'a, 'gcx, 'tcx>,
+               did: DefId,
+               name: Name,
+               discr: VariantDiscr,
+               fields: Vec<FieldDef>,
+               adt_kind: AdtKind,
+               ctor_kind: CtorKind)
+               -> Self
+    {
+        debug!("VariantDef::new({:?}, {:?}, {:?}, {:?}, {:?}, {:?})", did, name, discr, fields,
+               adt_kind, ctor_kind);
+        let mut flags = VariantFlags::NO_VARIANT_FLAGS;
+        if adt_kind == AdtKind::Struct && tcx.has_attr(did, "non_exhaustive") {
+            debug!("found non-exhaustive field list for {:?}", did);
+            flags = flags | VariantFlags::IS_FIELD_LIST_NON_EXHAUSTIVE;
+        }
+        VariantDef {
+            did,
+            name,
+            discr,
+            fields,
+            ctor_kind,
+            flags
+        }
+    }
+
+    #[inline]
+    pub fn is_field_list_non_exhaustive(&self) -> bool {
+        self.flags.intersects(VariantFlags::IS_FIELD_LIST_NON_EXHAUSTIVE)
+    }
+}
+
+impl_stable_hash_for!(struct VariantDef {
+    did,
+    name,
+    discr,
+    fields,
+    ctor_kind,
+    flags
+});
+
 #[derive(Copy, Clone, Debug, PartialEq, Eq, RustcEncodable, RustcDecodable)]
 pub enum VariantDiscr {
     /// Explicit value for this variant, i.e. `X = 123`.
@@ -1850,7 +1903,7 @@ impl_stable_hash_for!(struct ReprFlags {
 
 
 /// Represents the repr options provided by the user,
-#[derive(Copy, Clone, Eq, PartialEq, RustcEncodable, RustcDecodable, Default)]
+#[derive(Copy, Clone, Debug, Eq, PartialEq, RustcEncodable, RustcDecodable, Default)]
 pub struct ReprOptions {
     pub int: Option<attr::IntType>,
     pub align: u32,
@@ -1939,6 +1992,7 @@ impl<'a, 'gcx, 'tcx> AdtDef {
            kind: AdtKind,
            variants: Vec<VariantDef>,
            repr: ReprOptions) -> Self {
+        debug!("AdtDef::new({:?}, {:?}, {:?}, {:?})", did, kind, variants, repr);
         let mut flags = AdtFlags::NO_ADT_FLAGS;
         let attrs = tcx.get_attrs(did);
         if attr::contains_name(&attrs, "fundamental") {
@@ -1950,8 +2004,9 @@ impl<'a, 'gcx, 'tcx> AdtDef {
         if Some(did) == tcx.lang_items().owned_box() {
             flags = flags | AdtFlags::IS_BOX;
         }
-        if tcx.has_attr(did, "non_exhaustive") {
-            flags = flags | AdtFlags::IS_NON_EXHAUSTIVE;
+        if kind == AdtKind::Enum && tcx.has_attr(did, "non_exhaustive") {
+            debug!("found non-exhaustive variant list for {:?}", did);
+            flags = flags | AdtFlags::IS_VARIANT_LIST_NON_EXHAUSTIVE;
         }
         match kind {
             AdtKind::Enum => flags = flags | AdtFlags::IS_ENUM,
@@ -1982,8 +2037,8 @@ impl<'a, 'gcx, 'tcx> AdtDef {
     }
 
     #[inline]
-    pub fn is_non_exhaustive(&self) -> bool {
-        self.flags.intersects(AdtFlags::IS_NON_EXHAUSTIVE)
+    pub fn is_variant_list_non_exhaustive(&self) -> bool {
+        self.flags.intersects(AdtFlags::IS_VARIANT_LIST_NON_EXHAUSTIVE)
     }
 
     /// Returns the kind of the ADT - Struct or Enum.

src/librustc_metadata/decoder.rs

@@ -542,28 +542,36 @@ impl<'a, 'tcx> CrateMetadata {
                           self.def_path_table.def_path_hash(item_id))
     }
 
-    fn get_variant(&self, item: &Entry, index: DefIndex) -> ty::VariantDef {
+    fn get_variant(&self,
+                   tcx: TyCtxt<'a, 'tcx, 'tcx>,
+                   item: &Entry,
+                   index: DefIndex,
+                   adt_kind: ty::AdtKind)
+                   -> ty::VariantDef
+    {
         let data = match item.kind {
             EntryKind::Variant(data) |
             EntryKind::Struct(data, _) |
             EntryKind::Union(data, _) => data.decode(self),
             _ => bug!(),
         };
 
-        ty::VariantDef {
-            did: self.local_def_id(data.struct_ctor.unwrap_or(index)),
-            name: self.item_name(index).as_symbol(),
-            fields: item.children.decode(self).map(|index| {
+        ty::VariantDef::new(
+            tcx,
+            self.local_def_id(data.struct_ctor.unwrap_or(index)),
+            self.item_name(index).as_symbol(),
+            data.discr,
+            item.children.decode(self).map(|index| {
                 let f = self.entry(index);
                 ty::FieldDef {
                     did: self.local_def_id(index),
                     ident: Ident::from_interned_str(self.item_name(index)),
                     vis: f.visibility.decode(self)
                 }
             }).collect(),
-            discr: data.discr,
-            ctor_kind: data.ctor_kind,
-        }
+            adt_kind,
+            data.ctor_kind
+        )
     }
 
     pub fn get_adt_def(&self,
@@ -584,11 +592,11 @@ impl<'a, 'tcx> CrateMetadata {
             item.children
                 .decode(self)
                 .map(|index| {
-                    self.get_variant(&self.entry(index), index)
+                    self.get_variant(tcx, &self.entry(index), index, kind)
                 })
                 .collect()
         } else {
-            vec![self.get_variant(&item, item_id)]
+            vec![self.get_variant(tcx, &item, item_id, kind)]
         };
 
         tcx.alloc_adt_def(did, kind, variants, repr)

src/librustc_metadata/encoder.rs

@@ -740,7 +740,9 @@ impl<'a, 'b: 'a, 'tcx: 'b> IsolatedEncoder<'a, 'b, 'tcx> {
 
         // If the structure is marked as non_exhaustive then lower the visibility
         // to within the crate.
-        if adt_def.is_non_exhaustive() && ctor_vis == ty::Visibility::Public {
+        if adt_def.non_enum_variant().is_field_list_non_exhaustive() &&
+            ctor_vis == ty::Visibility::Public
+        {
             ctor_vis = ty::Visibility::Restricted(DefId::local(CRATE_DEF_INDEX));
         }
 

src/librustc_mir/hair/pattern/_match.rs

@@ -381,7 +381,7 @@ impl<'a, 'tcx> MatchCheckCtxt<'a, 'tcx> {
 
     fn is_non_exhaustive_enum(&self, ty: Ty<'tcx>) -> bool {
         match ty.sty {
-            ty::Adt(adt_def, ..) => adt_def.is_enum() && adt_def.is_non_exhaustive(),
+            ty::Adt(adt_def, ..) => adt_def.is_variant_list_non_exhaustive(),
             _ => false,
         }
     }

src/librustc_privacy/lib.rs

@@ -686,7 +686,9 @@ impl<'a, 'tcx> TypePrivacyVisitor<'a, 'tcx> {
                         // visibility to within the crate.
                         let struct_def_id = self.tcx.hir.get_parent_did(node_id);
                         let adt_def = self.tcx.adt_def(struct_def_id);
-                        if adt_def.is_non_exhaustive() && ctor_vis == ty::Visibility::Public {
+                        if adt_def.non_enum_variant().is_field_list_non_exhaustive()
+                            && ctor_vis == ty::Visibility::Public
+                        {
                             ctor_vis = ty::Visibility::Restricted(
                                 DefId::local(CRATE_DEF_INDEX));
                         }

src/librustc_typeck/check/_match.rs

@@ -950,7 +950,7 @@ https://doc.rust-lang.org/reference/types.html#trait-objects");
         }
 
         // Require `..` if struct has non_exhaustive attribute.
-        if adt.is_struct() && adt.is_non_exhaustive() && !adt.did.is_local() && !etc {
+        if variant.is_field_list_non_exhaustive() && !adt.did.is_local() && !etc {
             span_err!(tcx.sess, span, E0638,
                       "`..` required with {} marked as non-exhaustive",
                       kind_name);

src/librustc_typeck/check/mod.rs

@@ -3471,7 +3471,7 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
         // re-link the regions that EIfEO can erase.
         self.demand_eqtype(span, adt_ty_hint, adt_ty);
 
-        let (substs, adt_kind, kind_name) = match &adt_ty.sty{
+        let (substs, adt_kind, kind_name) = match &adt_ty.sty {
             &ty::Adt(adt, substs) => {
                 (substs, adt.adt_kind(), adt.variant_descr())
             }
@@ -3645,37 +3645,36 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                          base_expr: &'gcx Option<P<hir::Expr>>) -> Ty<'tcx>
     {
         // Find the relevant variant
-        let (variant, struct_ty) =
-        if let Some(variant_ty) = self.check_struct_path(qpath, expr.id) {
-            variant_ty
-        } else {
-            self.check_struct_fields_on_error(fields, base_expr);
-            return self.tcx.types.err;
-        };
+        let (variant, adt_ty) =
+            if let Some(variant_ty) = self.check_struct_path(qpath, expr.id) {
+                variant_ty
+            } else {
+                self.check_struct_fields_on_error(fields, base_expr);
+                return self.tcx.types.err;
+            };
 
         let path_span = match *qpath {
             hir::QPath::Resolved(_, ref path) => path.span,
             hir::QPath::TypeRelative(ref qself, _) => qself.span
         };
 
         // Prohibit struct expressions when non exhaustive flag is set.
-        if let ty::Adt(adt, _) = struct_ty.sty {
-            if !adt.did.is_local() && adt.is_non_exhaustive() {
-                span_err!(self.tcx.sess, expr.span, E0639,
-                          "cannot create non-exhaustive {} using struct expression",
-                          adt.variant_descr());
-            }
+        let adt = adt_ty.ty_adt_def().expect("`check_struct_path` returned non-ADT type");
+        if !adt.did.is_local() && variant.is_field_list_non_exhaustive() {
+            span_err!(self.tcx.sess, expr.span, E0639,
+                      "cannot create non-exhaustive {} using struct expression",
+                      adt.variant_descr());
         }
 
-        let error_happened = self.check_expr_struct_fields(struct_ty, expected, expr.id, path_span,
+        let error_happened = self.check_expr_struct_fields(adt_ty, expected, expr.id, path_span,
                                                            variant, fields, base_expr.is_none());
         if let &Some(ref base_expr) = base_expr {
             // If check_expr_struct_fields hit an error, do not attempt to populate
             // the fields with the base_expr. This could cause us to hit errors later
             // when certain fields are assumed to exist that in fact do not.
             if !error_happened {
-                self.check_expr_has_type_or_error(base_expr, struct_ty);
-                match struct_ty.sty {
+                self.check_expr_has_type_or_error(base_expr, adt_ty);
+                match adt_ty.sty {
                     ty::Adt(adt, substs) if adt.is_struct() => {
                         let fru_field_types = adt.non_enum_variant().fields.iter().map(|f| {
                             self.normalize_associated_types_in(expr.span, &f.ty(self.tcx, substs))
@@ -3693,8 +3692,8 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                 }
             }
         }
-        self.require_type_is_sized(struct_ty, expr.span, traits::StructInitializerSized);
-        struct_ty
+        self.require_type_is_sized(adt_ty, expr.span, traits::StructInitializerSized);
+        adt_ty
     }
 
 

src/librustc_typeck/collect.rs

@@ -549,12 +549,13 @@ fn convert_enum_variant_types<'a, 'tcx>(
     }
 }
 
-fn convert_struct_variant<'a, 'tcx>(
+fn convert_variant<'a, 'tcx>(
     tcx: TyCtxt<'a, 'tcx, 'tcx>,
     did: DefId,
     name: ast::Name,
     discr: ty::VariantDiscr,
     def: &hir::VariantData,
+    adt_kind: ty::AdtKind
 ) -> ty::VariantDef {
     let mut seen_fields: FxHashMap<ast::Ident, Span> = FxHashMap();
     let node_id = tcx.hir.as_local_node_id(did).unwrap();
@@ -585,13 +586,13 @@ fn convert_struct_variant<'a, 'tcx>(
             }
         })
         .collect();
-    ty::VariantDef {
+    ty::VariantDef::new(tcx,
         did,
         name,
         discr,
         fields,
-        ctor_kind: CtorKind::from_hir(def),
-    }
+        adt_kind,
+        CtorKind::from_hir(def))
 }
 
 fn adt_def<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> &'tcx ty::AdtDef {
@@ -621,7 +622,7 @@ fn adt_def<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> &'tcx ty::Ad
                         };
                         distance_from_explicit += 1;
 
-                        convert_struct_variant(tcx, did, v.node.name, discr, &v.node.data)
+                        convert_variant(tcx, did, v.node.name, discr, &v.node.data, AdtKind::Enum)
                     })
                     .collect(),
             )
@@ -635,23 +636,25 @@ fn adt_def<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> &'tcx ty::Ad
             };
             (
                 AdtKind::Struct,
-                vec![convert_struct_variant(
+                vec![convert_variant(
                     tcx,
                     ctor_id.unwrap_or(def_id),
                     item.name,
                     ty::VariantDiscr::Relative(0),
                     def,
+                    AdtKind::Struct
                 )],
             )
         }
         ItemKind::Union(ref def, _) => (
             AdtKind::Union,
-            vec![convert_struct_variant(
+            vec![convert_variant(
                 tcx,
                 def_id,
                 item.name,
                 ty::VariantDiscr::Relative(0),
                 def,
+                AdtKind::Union
             )],
         ),
         _ => bug!(),