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.

7 files changed, 87 insertions, 24 deletions

diff --git a/src/librustc/ty/mod.rs b/src/librustc/ty/mod.rs
index 77b4d32c397..c60de9c386e 100644
--- a/src/librustc/ty/mod.rs
+++ b/src/librustc/ty/mod.rs
@@ -1981,10 +1981,30 @@ impl<'a, 'gcx, 'tcx> AdtDef {
     }
 
     #[inline]
-    pub fn is_non_exhaustive(&self) -> bool {
+    fn is_non_exhaustive(&self) -> bool {
         self.flags.intersects(AdtFlags::IS_NON_EXHAUSTIVE)
     }
 
+    #[inline]
+    pub fn is_enum_non_exhaustive(&self) -> bool {
+        match self.adt_kind() {
+            AdtKind::Enum => self.is_non_exhaustive(),
+            AdtKind::Struct | AdtKind::Union => {
+                bug!("is_non_exhaustive_enum called on non-enum `{:?}`", self);
+            }
+        }
+    }
+
+    #[inline]
+    pub fn is_univariant_non_exhaustive(&self) -> bool {
+        match self.adt_kind() {
+            AdtKind::Struct | AdtKind::Union => self.is_non_exhaustive(),
+            AdtKind::Enum => {
+                bug!("is_non_exhaustive_enum called on non-enum `{:?}`", self);
+            }
+        }
+    }
+
     /// Returns the kind of the ADT - Struct or Enum.
     #[inline]
     pub fn adt_kind(&self) -> AdtKind {
@@ -1997,6 +2017,19 @@ impl<'a, 'gcx, 'tcx> AdtDef {
         }
     }
 
+    /// Return whether `variant` is non-exhaustive as a *struct* (i.e., whether
+    /// it can have additional fields).
+    pub fn is_variant_non_exhaustive(&self, _variant: &ty::VariantDef) -> bool {
+        match self.adt_kind() {
+            // A struct is non-exhaustive if it has a `#[non_exhaustive]` attribute.
+            AdtKind::Struct => self.is_non_exhaustive(),
+            // At this moment, all enum variants are exhaustive.
+            AdtKind::Enum => false,
+            // All unions are "exhaustive", as far as that makes sense.
+            AdtKind::Union => false,
+        }
+    }
+
     pub fn descr(&self) -> &'static str {
         match self.adt_kind() {
             AdtKind::Struct => "struct",
diff --git a/src/librustc_metadata/encoder.rs b/src/librustc_metadata/encoder.rs
index 8219ec3df24..27f4577c442 100644
--- a/src/librustc_metadata/encoder.rs
+++ b/src/librustc_metadata/encoder.rs
@@ -740,7 +740,7 @@ 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.is_univariant_non_exhaustive() && ctor_vis == ty::Visibility::Public {
             ctor_vis = ty::Visibility::Restricted(DefId::local(CRATE_DEF_INDEX));
         }
 
diff --git a/src/librustc_mir/hair/pattern/_match.rs b/src/librustc_mir/hair/pattern/_match.rs
index e9d65caf087..4f14a45bfc8 100644
--- a/src/librustc_mir/hair/pattern/_match.rs
+++ b/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_enum() && adt_def.is_enum_non_exhaustive(),
             _ => false,
         }
     }
diff --git a/src/librustc_privacy/lib.rs b/src/librustc_privacy/lib.rs
index f68f2d0da68..ea13a3d0033 100644
--- a/src/librustc_privacy/lib.rs
+++ b/src/librustc_privacy/lib.rs
@@ -684,7 +684,9 @@ 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.is_univariant_non_exhaustive()
+                            && ctor_vis == ty::Visibility::Public
+                        {
                             ctor_vis = ty::Visibility::Restricted(
                                 DefId::local(CRATE_DEF_INDEX));
                         }
diff --git a/src/librustc_typeck/check/_match.rs b/src/librustc_typeck/check/_match.rs
index ae68584f244..b4dcea0eb32 100644
--- a/src/librustc_typeck/check/_match.rs
+++ b/src/librustc_typeck/check/_match.rs
@@ -948,7 +948,7 @@ 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 adt.is_variant_non_exhaustive(variant) && !adt.did.is_local() && !etc {
             span_err!(tcx.sess, span, E0638,
                       "`..` required with {} marked as non-exhaustive",
                       kind_name);
diff --git a/src/librustc_typeck/check/mod.rs b/src/librustc_typeck/check/mod.rs
index 2b33f289346..d4013b10c31 100644
--- a/src/librustc_typeck/check/mod.rs
+++ b/src/librustc_typeck/check/mod.rs
@@ -3465,7 +3465,7 @@ 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())
             }
@@ -3639,13 +3639,13 @@ 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,
@@ -3653,23 +3653,22 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
         };
 
         // 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() && adt.is_variant_non_exhaustive(variant) {
+            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))
@@ -3687,8 +3686,8 @@ 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
     }
 
 
diff --git a/src/test/run-pass/rfc-2008-non-exhaustive/enums.rs b/src/test/run-pass/rfc-2008-non-exhaustive/enums.rs
index 9d41eca8fe5..83fb24cda08 100644
--- a/src/test/run-pass/rfc-2008-non-exhaustive/enums.rs
+++ b/src/test/run-pass/rfc-2008-non-exhaustive/enums.rs
@@ -30,4 +30,33 @@ fn main() {
     match enum_unit {
         _ => "no error with only wildcard"
     };
+
+
+    // issue #53549 - check that variant constructors can still be called normally.
+
+    match NonExhaustiveEnum::Unit {
+        NonExhaustiveEnum::Unit => {},
+        _ => {}
+    };
+
+    match NonExhaustiveEnum::Tuple(2) {
+        NonExhaustiveEnum::Tuple(2) => {},
+        _ => {}
+    };
+
+    match (NonExhaustiveEnum::Unit {}) {
+        NonExhaustiveEnum::Unit {} => {},
+        _ => {}
+    };
+
+    match (NonExhaustiveEnum::Tuple { 0: 2 }) {
+        NonExhaustiveEnum::Tuple { 0: 2 } => {},
+        _ => {}
+    };
+
+    match (NonExhaustiveEnum::Struct { field: 2 }) {
+        NonExhaustiveEnum::Struct { field: 2 } => {},
+        _ => {}
+    };
+
 }