Add helper methods checking for "#[non_exhaustive] that's active"

A check for `#[non_exhaustive]` is often done in combination with
checking whether the type is local to the crate, in a variety of ways.
Create a helper method and standardize on it as the way to check for
this.

Author: meithecatte

compiler/rustc_hir_typeck/src/cast.rs

@@ -42,7 +42,6 @@ use rustc_middle::ty::error::TypeError;
 use rustc_middle::ty::{self, Ty, TyCtxt, TypeAndMut, TypeVisitableExt, VariantDef};
 use rustc_middle::{bug, span_bug};
 use rustc_session::lint;
-use rustc_span::def_id::LOCAL_CRATE;
 use rustc_span::{DUMMY_SP, Span, sym};
 use rustc_trait_selection::infer::InferCtxtExt;
 use rustc_type_ir::elaborate;
@@ -789,7 +788,7 @@ impl<'a, 'tcx> CastCheck<'tcx> {
             _ => return Err(CastError::NonScalar),
         };
         if let ty::Adt(adt_def, _) = *self.expr_ty.kind()
-            && adt_def.did().krate != LOCAL_CRATE
+            && !adt_def.did().is_local()
             && adt_def.variants().iter().any(VariantDef::is_field_list_non_exhaustive)
         {
             return Err(CastError::ForeignNonExhaustiveAdt);

compiler/rustc_hir_typeck/src/expr.rs

@@ -1963,7 +1963,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
         // Prohibit struct expressions when non-exhaustive flag is set.
         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() {
+        if variant.field_list_has_applicable_non_exhaustive() {
             self.dcx()
                 .emit_err(StructExprNonExhaustive { span: expr.span, what: adt.variant_descr() });
         }

compiler/rustc_hir_typeck/src/expr_use_visitor.rs

@@ -20,7 +20,7 @@ use rustc_middle::hir::place::ProjectionKind;
 pub use rustc_middle::hir::place::{Place, PlaceBase, PlaceWithHirId, Projection};
 use rustc_middle::mir::FakeReadCause;
 use rustc_middle::ty::{
-    self, AdtKind, BorrowKind, Ty, TyCtxt, TypeFoldable, TypeVisitableExt as _, adjustment,
+    self, BorrowKind, Ty, TyCtxt, TypeFoldable, TypeVisitableExt as _, adjustment,
 };
 use rustc_middle::{bug, span_bug};
 use rustc_span::{ErrorGuaranteed, Span};
@@ -1834,14 +1834,7 @@ impl<'tcx, Cx: TypeInformationCtxt<'tcx>, D: Delegate<'tcx>> ExprUseVisitor<'tcx
             // to assume that more cases will be added to the variant in the future. This mean
             // that we should handle non-exhaustive SingleVariant the same way we would handle
             // a MultiVariant.
-            // If the variant is not local it must be defined in another crate.
-            let is_non_exhaustive = match def.adt_kind() {
-                AdtKind::Struct | AdtKind::Union => {
-                    def.non_enum_variant().is_field_list_non_exhaustive()
-                }
-                AdtKind::Enum => def.is_variant_list_non_exhaustive(),
-            };
-            def.variants().len() > 1 || (!def.did().is_local() && is_non_exhaustive)
+            def.variants().len() > 1 || def.variant_list_has_applicable_non_exhaustive()
         } else {
             false
         }

compiler/rustc_hir_typeck/src/pat.rs

@@ -1722,7 +1722,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         };
 
         // Require `..` if struct has non_exhaustive attribute.
-        let non_exhaustive = variant.is_field_list_non_exhaustive() && !adt.did().is_local();
+        let non_exhaustive = variant.field_list_has_applicable_non_exhaustive();
         if non_exhaustive && !has_rest_pat {
             self.error_foreign_non_exhaustive_spat(pat, adt.variant_descr(), fields.is_empty());
         }

compiler/rustc_lint/src/types.rs

@@ -1207,9 +1207,7 @@ impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
                             };
                         }
 
-                        let is_non_exhaustive =
-                            def.non_enum_variant().is_field_list_non_exhaustive();
-                        if is_non_exhaustive && !def.did().is_local() {
+                        if def.non_enum_variant().field_list_has_applicable_non_exhaustive() {
                             return FfiUnsafe {
                                 ty,
                                 reason: if def.is_struct() {
@@ -1262,14 +1260,12 @@ impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
                             };
                         }
 
-                        use improper_ctypes::{
-                            check_non_exhaustive_variant, non_local_and_non_exhaustive,
-                        };
+                        use improper_ctypes::check_non_exhaustive_variant;
 
-                        let non_local_def = non_local_and_non_exhaustive(def);
+                        let non_exhaustive = def.variant_list_has_applicable_non_exhaustive();
                         // Check the contained variants.
                         let ret = def.variants().iter().try_for_each(|variant| {
-                            check_non_exhaustive_variant(non_local_def, variant)
+                            check_non_exhaustive_variant(non_exhaustive, variant)
                                 .map_break(|reason| FfiUnsafe { ty, reason, help: None })?;
 
                             match self.check_variant_for_ffi(acc, ty, def, variant, args) {

compiler/rustc_lint/src/types/improper_ctypes.rs

@@ -15,13 +15,13 @@ use crate::fluent_generated as fluent;
 /// so we don't need the lint to account for it.
 /// e.g. going from enum Foo { A, B, C } to enum Foo { A, B, C, D(u32) }.
 pub(crate) fn check_non_exhaustive_variant(
-    non_local_def: bool,
+    non_exhaustive_variant_list: bool,
     variant: &ty::VariantDef,
 ) -> ControlFlow<DiagMessage, ()> {
     // non_exhaustive suggests it is possible that someone might break ABI
     // see: https://github.com/rust-lang/rust/issues/44109#issuecomment-537583344
     // so warn on complex enums being used outside their crate
-    if non_local_def {
+    if non_exhaustive_variant_list {
         // which is why we only warn about really_tagged_union reprs from https://rust.tf/rfc2195
         // with an enum like `#[repr(u8)] enum Enum { A(DataA), B(DataB), }`
         // but exempt enums with unit ctors like C's (e.g. from rust-bindgen)
@@ -30,8 +30,7 @@ pub(crate) fn check_non_exhaustive_variant(
         }
     }
 
-    let non_exhaustive_variant_fields = variant.is_field_list_non_exhaustive();
-    if non_exhaustive_variant_fields && !variant.def_id.is_local() {
+    if variant.field_list_has_applicable_non_exhaustive() {
         return ControlFlow::Break(fluent::lint_improper_ctypes_non_exhaustive_variant);
     }
 
@@ -42,10 +41,3 @@ fn variant_has_complex_ctor(variant: &ty::VariantDef) -> bool {
     // CtorKind::Const means a "unit" ctor
     !matches!(variant.ctor_kind(), Some(CtorKind::Const))
 }
-
-// non_exhaustive suggests it is possible that someone might break ABI
-// see: https://github.com/rust-lang/rust/issues/44109#issuecomment-537583344
-// so warn on complex enums being used outside their crate
-pub(crate) fn non_local_and_non_exhaustive(def: ty::AdtDef<'_>) -> bool {
-    def.is_variant_list_non_exhaustive() && !def.did().is_local()
-}

compiler/rustc_middle/src/ty/adt.rs

@@ -329,11 +329,22 @@ impl<'tcx> AdtDef<'tcx> {
     }
 
     /// Returns `true` if the variant list of this ADT is `#[non_exhaustive]`.
+    ///
+    /// Note that this function will return `true` even if the ADT has been
+    /// defined in the crate currently being compiled. If that's not what you
+    /// want, see [`Self::variant_list_has_applicable_non_exhaustive`].
     #[inline]
     pub fn is_variant_list_non_exhaustive(self) -> bool {
         self.flags().contains(AdtFlags::IS_VARIANT_LIST_NON_EXHAUSTIVE)
     }
 
+    /// Returns `true` if the variant list of this ADT is `#[non_exhaustive]`
+    /// and has been defined in another crate.
+    #[inline]
+    pub fn variant_list_has_applicable_non_exhaustive(self) -> bool {
+        self.is_variant_list_non_exhaustive() && !self.did().is_local()
+    }
+
     /// Returns the kind of the ADT.
     #[inline]
     pub fn adt_kind(self) -> AdtKind {

compiler/rustc_middle/src/ty/inhabitedness/mod.rs

@@ -107,7 +107,7 @@ impl<'tcx> Ty<'tcx> {
             // For now, unions 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() => {
+            Adt(adt, _) if adt.variant_list_has_applicable_non_exhaustive() => {
                 InhabitedPredicate::True
             }
             Never => InhabitedPredicate::False,

compiler/rustc_middle/src/ty/mod.rs

@@ -1212,12 +1212,23 @@ impl VariantDef {
         }
     }
 
-    /// Is this field list non-exhaustive?
+    /// Returns `true` if the field list of this variant is `#[non_exhaustive]`.
+    ///
+    /// Note that this function will return `true` even if the type has been
+    /// defined in the crate currently being compiled. If that's not what you
+    /// want, see [`Self::field_list_has_applicable_non_exhaustive`].
     #[inline]
     pub fn is_field_list_non_exhaustive(&self) -> bool {
         self.flags.intersects(VariantFlags::IS_FIELD_LIST_NON_EXHAUSTIVE)
     }
 
+    /// Returns `true` if the field list of this variant is `#[non_exhaustive]`
+    /// and the type has been defined in another crate.
+    #[inline]
+    pub fn field_list_has_applicable_non_exhaustive(&self) -> bool {
+        self.is_field_list_non_exhaustive() && !self.def_id.is_local()
+    }
+
     /// Computes the `Ident` of this variant by looking up the `Span`
     pub fn ident(&self, tcx: TyCtxt<'_>) -> Ident {
         Ident::new(self.name, tcx.def_ident_span(self.def_id).unwrap())

compiler/rustc_mir_build/src/builder/matches/match_pair.rs

@@ -223,8 +223,7 @@ impl<'tcx> MatchPairTree<'tcx> {
                             .inhabited_predicate(cx.tcx, adt_def)
                             .instantiate(cx.tcx, args)
                             .apply_ignore_module(cx.tcx, cx.infcx.typing_env(cx.param_env))
-                }) && (adt_def.did().is_local()
-                    || !adt_def.is_variant_list_non_exhaustive());
+                }) && !adt_def.variant_list_has_applicable_non_exhaustive();
                 if irrefutable {
                     default_irrefutable()
                 } else {