Fix diagnostic for matching/creating x-crate re-exported tuple structs with private fields.

The more helpful diagnostic already existed but wasn't working if the
struct in question was a re-export from a different crate.

compiler/rustc_metadata/src/rmeta/decoder.rs

@@ -27,7 +27,7 @@ use rustc_middle::middle::exported_symbols::{ExportedSymbol, SymbolExportLevel};
 use rustc_middle::mir::interpret::{AllocDecodingSession, AllocDecodingState};
 use rustc_middle::mir::{self, Body, Promoted};
 use rustc_middle::ty::codec::TyDecoder;
-use rustc_middle::ty::{self, Ty, TyCtxt};
+use rustc_middle::ty::{self, Ty, TyCtxt, Visibility};
 use rustc_serialize::{opaque, Decodable, Decoder};
 use rustc_session::Session;
 use rustc_span::hygiene::ExpnDataDecodeMode;
@@ -1305,6 +1305,17 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
             .collect()
     }
 
+    fn get_struct_field_visibilities(&self, id: DefIndex) -> Vec<Visibility> {
+        self.root
+            .tables
+            .children
+            .get(self, id)
+            .unwrap_or_else(Lazy::empty)
+            .decode(self)
+            .map(|field_index| self.get_visibility(field_index))
+            .collect()
+    }
+
     fn get_inherent_implementations_for_type(
         &self,
         tcx: TyCtxt<'tcx>,

compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs

@@ -8,7 +8,7 @@ use rustc_ast::expand::allocator::AllocatorKind;
 use rustc_data_structures::stable_map::FxHashMap;
 use rustc_data_structures::svh::Svh;
 use rustc_hir as hir;
-use rustc_hir::def::DefKind;
+use rustc_hir::def::{CtorKind, DefKind};
 use rustc_hir::def_id::{CrateNum, DefId, DefIdMap, CRATE_DEF_INDEX, LOCAL_CRATE};
 use rustc_hir::definitions::{DefKey, DefPath, DefPathHash};
 use rustc_middle::hir::exports::Export;
@@ -17,7 +17,7 @@ use rustc_middle::middle::cstore::{CrateSource, CrateStore, EncodedMetadata};
 use rustc_middle::middle::exported_symbols::ExportedSymbol;
 use rustc_middle::middle::stability::DeprecationEntry;
 use rustc_middle::ty::query::Providers;
-use rustc_middle::ty::{self, TyCtxt};
+use rustc_middle::ty::{self, TyCtxt, Visibility};
 use rustc_session::utils::NativeLibKind;
 use rustc_session::{CrateDisambiguator, Session};
 use rustc_span::source_map::{Span, Spanned};
@@ -392,6 +392,20 @@ impl CStore {
         self.get_crate_data(def.krate).get_struct_field_names(def.index, sess)
     }
 
+    pub fn struct_field_visibilities_untracked(&self, def: DefId) -> Vec<Visibility> {
+        self.get_crate_data(def.krate).get_struct_field_visibilities(def.index)
+    }
+
+    pub fn ctor_def_id_and_kind_untracked(&self, def: DefId) -> Option<(DefId, CtorKind)> {
+        self.get_crate_data(def.krate).get_ctor_def_id(def.index).map(|ctor_def_id| {
+            (ctor_def_id, self.get_crate_data(def.krate).get_ctor_kind(def.index))
+        })
+    }
+
+    pub fn visibility_untracked(&self, def: DefId) -> Visibility {
+        self.get_crate_data(def.krate).get_visibility(def.index)
+    }
+
     pub fn item_children_untracked(
         &self,
         def_id: DefId,

compiler/rustc_resolve/src/build_reduced_graph.rs

@@ -995,7 +995,20 @@ impl<'a, 'b> BuildReducedGraphVisitor<'a, 'b> {
         // Record some extra data for better diagnostics.
         let cstore = self.r.cstore();
         match res {
-            Res::Def(DefKind::Struct | DefKind::Union, def_id) => {
+            Res::Def(DefKind::Struct, def_id) => {
+                let field_names = cstore.struct_field_names_untracked(def_id, self.r.session);
+                let ctor = cstore.ctor_def_id_and_kind_untracked(def_id);
+                if let Some((ctor_def_id, ctor_kind)) = ctor {
+                    let ctor_res = Res::Def(DefKind::Ctor(CtorOf::Struct, ctor_kind), ctor_def_id);
+                    let ctor_vis = cstore.visibility_untracked(ctor_def_id);
+                    let field_visibilities = cstore.struct_field_visibilities_untracked(def_id);
+                    self.r
+                        .struct_constructors
+                        .insert(def_id, (ctor_res, ctor_vis, field_visibilities));
+                }
+                self.insert_field_names(def_id, field_names);
+            }
+            Res::Def(DefKind::Union, def_id) => {
                 let field_names = cstore.struct_field_names_untracked(def_id, self.r.session);
                 self.insert_field_names(def_id, field_names);
             }
@@ -1007,12 +1020,6 @@ impl<'a, 'b> BuildReducedGraphVisitor<'a, 'b> {
                     self.r.has_self.insert(def_id);
                 }
             }
-            Res::Def(DefKind::Ctor(CtorOf::Struct, ..), def_id) => {
-                let parent = cstore.def_key(def_id).parent;
-                if let Some(struct_def_id) = parent.map(|index| DefId { index, ..def_id }) {
-                    self.r.struct_constructors.insert(struct_def_id, (res, vis, vec![]));
-                }
-            }
             _ => {}
         }
     }