Rollup of 3 pull requests

compiler/rustc_borrowck/src/diagnostics/move_errors.rs

@@ -9,7 +9,8 @@ use rustc_middle::bug;
 use rustc_middle::mir::*;
 use rustc_middle::ty::{self, Ty, TyCtxt};
 use rustc_mir_dataflow::move_paths::{LookupResult, MovePathIndex};
-use rustc_span::{BytePos, ExpnKind, MacroKind, Span};
+use rustc_span::def_id::DefId;
+use rustc_span::{BytePos, DUMMY_SP, ExpnKind, MacroKind, Span};
 use rustc_trait_selection::error_reporting::traits::FindExprBySpan;
 use rustc_trait_selection::infer::InferCtxtExt;
 use tracing::debug;
@@ -507,12 +508,18 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
                 );
 
                 let closure_span = tcx.def_span(def_id);
+
                 self.cannot_move_out_of(span, &place_description)
                     .with_span_label(upvar_span, "captured outer variable")
                     .with_span_label(
                         closure_span,
                         format!("captured by this `{closure_kind}` closure"),
                     )
+                    .with_span_help(
+                        self.get_closure_bound_clause_span(*def_id),
+                        "`Fn` and `FnMut` closures require captured values to be able to be \
+                         consumed multiple times, but an `FnOnce` consume them only once",
+                    )
             }
             _ => {
                 let source = self.borrowed_content_source(deref_base);
@@ -561,6 +568,47 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
         err
     }
 
+    fn get_closure_bound_clause_span(&self, def_id: DefId) -> Span {
+        let tcx = self.infcx.tcx;
+        let typeck_result = tcx.typeck(self.mir_def_id());
+        // Check whether the closure is an argument to a call, if so,
+        // get the instantiated where-bounds of that call.
+        let closure_hir_id = tcx.local_def_id_to_hir_id(def_id.expect_local());
+        let hir::Node::Expr(parent) = tcx.parent_hir_node(closure_hir_id) else { return DUMMY_SP };
+
+        let predicates = match parent.kind {
+            hir::ExprKind::Call(callee, _) => {
+                let Some(ty) = typeck_result.node_type_opt(callee.hir_id) else { return DUMMY_SP };
+                let ty::FnDef(fn_def_id, args) = ty.kind() else { return DUMMY_SP };
+                tcx.predicates_of(fn_def_id).instantiate(tcx, args)
+            }
+            hir::ExprKind::MethodCall(..) => {
+                let Some((_, method)) = typeck_result.type_dependent_def(parent.hir_id) else {
+                    return DUMMY_SP;
+                };
+                let args = typeck_result.node_args(parent.hir_id);
+                tcx.predicates_of(method).instantiate(tcx, args)
+            }
+            _ => return DUMMY_SP,
+        };
+
+        // Check whether one of the where-bounds requires the closure to impl `Fn[Mut]`.
+        for (pred, span) in predicates.predicates.iter().zip(predicates.spans.iter()) {
+            if let Some(clause) = pred.as_trait_clause()
+                && let ty::Closure(clause_closure_def_id, _) = clause.self_ty().skip_binder().kind()
+                && *clause_closure_def_id == def_id
+                && (tcx.lang_items().fn_mut_trait() == Some(clause.def_id())
+                    || tcx.lang_items().fn_trait() == Some(clause.def_id()))
+            {
+                // Found `<TyOfCapturingClosure as FnMut>`
+                // We point at the `Fn()` or `FnMut()` bound that coerced the closure, which
+                // could be changed to `FnOnce()` to avoid the move error.
+                return *span;
+            }
+        }
+        DUMMY_SP
+    }
+
     fn add_move_hints(&self, error: GroupedMoveError<'tcx>, err: &mut Diag<'_>, span: Span) {
         match error {
             GroupedMoveError::MovesFromPlace { mut binds_to, move_from, .. } => {

compiler/rustc_errors/src/diagnostic.rs

@@ -847,17 +847,18 @@ impl<'a, G: EmissionGuarantee> Diag<'a, G> {
         self
     }
 
+    with_fn! { with_span_help,
     /// Prints the span with some help above it.
     /// This is like [`Diag::help()`], but it gets its own span.
     #[rustc_lint_diagnostics]
-    pub fn span_help<S: Into<MultiSpan>>(
+    pub fn span_help(
         &mut self,
-        sp: S,
+        sp: impl Into<MultiSpan>,
         msg: impl Into<SubdiagMessage>,
     ) -> &mut Self {
         self.sub(Level::Help, msg, sp.into());
         self
-    }
+    } }
 
     /// Disallow attaching suggestions to this diagnostic.
     /// Any suggestions attached e.g. with the `span_suggestion_*` methods

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

@@ -395,6 +395,7 @@ provide! { tcx, def_id, other, cdata,
 
     crate_extern_paths => { cdata.source().paths().cloned().collect() }
     expn_that_defined => { cdata.get_expn_that_defined(def_id.index, tcx.sess) }
+    default_field => { cdata.get_default_field(def_id.index) }
     is_doc_hidden => { cdata.get_attr_flags(def_id.index).contains(AttrFlags::IS_DOC_HIDDEN) }
     doc_link_resolutions => { tcx.arena.alloc(cdata.get_doc_link_resolutions(def_id.index)) }
     doc_link_traits_in_scope => {

compiler/rustc_middle/src/query/mod.rs

@@ -1864,6 +1864,12 @@ rustc_queries! {
         feedable
     }
 
+    /// Returns whether the field corresponding to the `DefId` has a default field value.
+    query default_field(def_id: DefId) -> Option<DefId> {
+        desc { |tcx| "looking up the `const` corresponding to the default for `{}`", tcx.def_path_str(def_id) }
+        separate_provide_extern
+    }
+
     query check_well_formed(key: LocalDefId) -> Result<(), ErrorGuaranteed> {
         desc { |tcx| "checking that `{}` is well-formed", tcx.def_path_str(key) }
         return_result_from_ensure_ok

compiler/rustc_resolve/src/build_reduced_graph.rs

@@ -420,14 +420,18 @@ impl<'a, 'ra, 'tcx> BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
             // The fields are not expanded yet.
             return;
         }
-        let fields = fields
+        let field_name = |i, field: &ast::FieldDef| {
+            field.ident.unwrap_or_else(|| Ident::from_str_and_span(&format!("{i}"), field.span))
+        };
+        let field_names: Vec<_> =
+            fields.iter().enumerate().map(|(i, field)| field_name(i, field)).collect();
+        let defaults = fields
             .iter()
             .enumerate()
-            .map(|(i, field)| {
-                field.ident.unwrap_or_else(|| Ident::from_str_and_span(&format!("{i}"), field.span))
-            })
+            .filter_map(|(i, field)| field.default.as_ref().map(|_| field_name(i, field).name))
             .collect();
-        self.r.field_names.insert(def_id, fields);
+        self.r.field_names.insert(def_id, field_names);
+        self.r.field_defaults.insert(def_id, defaults);
     }
 
     fn insert_field_visibilities_local(&mut self, def_id: DefId, fields: &[ast::FieldDef]) {

compiler/rustc_resolve/src/diagnostics.rs

@@ -1943,8 +1943,15 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
     }
 
     fn report_privacy_error(&mut self, privacy_error: &PrivacyError<'ra>) {
-        let PrivacyError { ident, binding, outermost_res, parent_scope, single_nested, dedup_span } =
-            *privacy_error;
+        let PrivacyError {
+            ident,
+            binding,
+            outermost_res,
+            parent_scope,
+            single_nested,
+            dedup_span,
+            ref source,
+        } = *privacy_error;
 
         let res = binding.res();
         let ctor_fields_span = self.ctor_fields_span(binding);
@@ -1960,6 +1967,8 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         let mut err =
             self.dcx().create_err(errors::IsPrivate { span: ident.span, ident_descr, ident });
 
+        self.mention_default_field_values(source, ident, &mut err);
+
         let mut not_publicly_reexported = false;
         if let Some((this_res, outer_ident)) = outermost_res {
             let import_suggestions = self.lookup_import_candidates(
@@ -2141,6 +2150,85 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         err.emit();
     }
 
+    /// When a private field is being set that has a default field value, we suggest using `..` and
+    /// setting the value of that field implicitly with its default.
+    ///
+    /// If we encounter code like
+    /// ```text
+    /// struct Priv;
+    /// pub struct S {
+    ///     pub field: Priv = Priv,
+    /// }
+    /// ```
+    /// which is used from a place where `Priv` isn't accessible
+    /// ```text
+    /// let _ = S { field: m::Priv1 {} };
+    /// //                    ^^^^^ private struct
+    /// ```
+    /// we will suggest instead using the `default_field_values` syntax instead:
+    /// ```text
+    /// let _ = S { .. };
+    /// ```
+    fn mention_default_field_values(
+        &self,
+        source: &Option<ast::Expr>,
+        ident: Ident,
+        err: &mut Diag<'_>,
+    ) {
+        let Some(expr) = source else { return };
+        let ast::ExprKind::Struct(struct_expr) = &expr.kind else { return };
+        // We don't have to handle type-relative paths because they're forbidden in ADT
+        // expressions, but that would change with `#[feature(more_qualified_paths)]`.
+        let Some(Res::Def(_, def_id)) =
+            self.partial_res_map[&struct_expr.path.segments.iter().last().unwrap().id].full_res()
+        else {
+            return;
+        };
+        let Some(default_fields) = self.field_defaults(def_id) else { return };
+        if struct_expr.fields.is_empty() {
+            return;
+        }
+        let last_span = struct_expr.fields.iter().last().unwrap().span;
+        let mut iter = struct_expr.fields.iter().peekable();
+        let mut prev: Option<Span> = None;
+        while let Some(field) = iter.next() {
+            if field.expr.span.overlaps(ident.span) {
+                err.span_label(field.ident.span, "while setting this field");
+                if default_fields.contains(&field.ident.name) {
+                    let sugg = if last_span == field.span {
+                        vec![(field.span, "..".to_string())]
+                    } else {
+                        vec![
+                            (
+                                // Account for trailing commas and ensure we remove them.
+                                match (prev, iter.peek()) {
+                                    (_, Some(next)) => field.span.with_hi(next.span.lo()),
+                                    (Some(prev), _) => field.span.with_lo(prev.hi()),
+                                    (None, None) => field.span,
+                                },
+                                String::new(),
+                            ),
+                            (last_span.shrink_to_hi(), ", ..".to_string()),
+                        ]
+                    };
+                    err.multipart_suggestion_verbose(
+                        format!(
+                            "the type `{ident}` of field `{}` is private, but you can construct \
+                             the default value defined for it in `{}` using `..` in the struct \
+                             initializer expression",
+                            field.ident,
+                            self.tcx.item_name(def_id),
+                        ),
+                        sugg,
+                        Applicability::MachineApplicable,
+                    );
+                    break;
+                }
+            }
+            prev = Some(field.span);
+        }
+    }
+
     pub(crate) fn find_similarly_named_module_or_crate(
         &self,
         ident: Symbol,

compiler/rustc_resolve/src/ident.rs

@@ -1029,6 +1029,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                     binding,
                     dedup_span: path_span,
                     outermost_res: None,
+                    source: None,
                     parent_scope: *parent_scope,
                     single_nested: path_span != root_span,
                 });
@@ -1435,7 +1436,16 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         parent_scope: &ParentScope<'ra>,
         ignore_import: Option<Import<'ra>>,
     ) -> PathResult<'ra> {
-        self.resolve_path_with_ribs(path, opt_ns, parent_scope, None, None, None, ignore_import)
+        self.resolve_path_with_ribs(
+            path,
+            opt_ns,
+            parent_scope,
+            None,
+            None,
+            None,
+            None,
+            ignore_import,
+        )
     }
     #[instrument(level = "debug", skip(self))]
     pub(crate) fn resolve_path<'r>(
@@ -1451,6 +1461,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             path,
             opt_ns,
             parent_scope,
+            None,
             finalize,
             None,
             ignore_binding,
@@ -1463,6 +1474,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         path: &[Segment],
         opt_ns: Option<Namespace>, // `None` indicates a module path in import
         parent_scope: &ParentScope<'ra>,
+        source: Option<PathSource<'_, '_, '_>>,
         finalize: Option<Finalize>,
         ribs: Option<&PerNS<Vec<Rib<'ra>>>>,
         ignore_binding: Option<NameBinding<'ra>>,
@@ -1645,6 +1657,11 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                     if finalize.is_some() {
                         for error in &mut self.get_mut().privacy_errors[privacy_errors_len..] {
                             error.outermost_res = Some((res, ident));
+                            error.source = match source {
+                                Some(PathSource::Struct(Some(expr)))
+                                | Some(PathSource::Expr(Some(expr))) => Some(expr.clone()),
+                                _ => None,
+                            };
                         }
                     }