Suggest making private tuple struct field public

Fix #52144.

compiler/rustc_resolve/src/build_reduced_graph.rs

@@ -331,7 +331,9 @@ impl<'a, 'b> BuildReducedGraphVisitor<'a, 'b> {
             .iter()
             .map(|field| respan(field.span, field.ident.map_or(kw::Empty, |ident| ident.name)))
             .collect();
+        let field_vis = vdata.fields().iter().map(|field| field.vis.span).collect();
         self.r.field_names.insert(def_id, field_names);
+        self.r.field_visibility_spans.insert(def_id, field_vis);
     }
 
     fn insert_field_names_extern(&mut self, def_id: DefId) {

compiler/rustc_resolve/src/late/diagnostics.rs

@@ -1451,6 +1451,26 @@ impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
                         .collect();
 
                     if non_visible_spans.len() > 0 {
+                        if let Some(visibility_spans) = self.r.field_visibility_spans.get(&def_id) {
+                            err.multipart_suggestion_verbose(
+                                &format!(
+                                    "consider making the field{} publicly accessible",
+                                    pluralize!(visibility_spans.len())
+                                ),
+                                visibility_spans
+                                    .iter()
+                                    .map(|span| {
+                                        (
+                                            *span,
+                                            if span.lo() == span.hi() { "pub " } else { "pub" }
+                                                .to_string(),
+                                        )
+                                    })
+                                    .collect(),
+                                Applicability::MaybeIncorrect,
+                            );
+                        }
+
                         let mut m: MultiSpan = non_visible_spans.clone().into();
                         non_visible_spans
                             .into_iter()

compiler/rustc_resolve/src/lib.rs

@@ -881,6 +881,10 @@ pub struct Resolver<'a> {
     /// Used for hints during error reporting.
     field_names: FxHashMap<DefId, Vec<Spanned<Symbol>>>,
 
+    /// Span of the privacy modifier in fields of an item `DefId` accessible with dot syntax.
+    /// Used for hints during error reporting.
+    field_visibility_spans: FxHashMap<DefId, Vec<Span>>,
+
     /// All imports known to succeed or fail.
     determined_imports: Vec<&'a Import<'a>>,
 
@@ -1268,6 +1272,7 @@ impl<'a> Resolver<'a> {
 
             has_self: FxHashSet::default(),
             field_names: FxHashMap::default(),
+            field_visibility_spans: FxHashMap::default(),
 
             determined_imports: Vec::new(),
             indeterminate_imports: Vec::new(),