Auto merge of rust-lang#107727 - Dylan-DPC:rollup-b1yexcl, r=Dylan-DPC

Rollup of 5 pull requests

Successful merges:

 - rust-lang#107553 (Suggest std::ptr::null if literal 0 is given to a raw pointer function argument)
 - rust-lang#107580 (Recover from lifetimes with default lifetimes in generic args)
 - rust-lang#107669 (rustdoc: combine duplicate rules in ayu CSS)
 - rust-lang#107685 (Suggest adding a return type for async functions)
 - rust-lang#107687 (Adapt SROA MIR opt for aggregated MIR)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup

compiler/rustc_error_messages/locales/en-US/parse.ftl

@@ -475,6 +475,9 @@ parse_unexpected_token_after_struct_name_found_other = expected `where`, `{"{"}`
 parse_unexpected_self_in_generic_parameters = unexpected keyword `Self` in generic parameters
     .note = you cannot use `Self` as a generic parameter because it is reserved for associated items
 
+parse_unexpected_default_value_for_lifetime_in_generic_parameters = unexpected default lifetime parameter
+    .label = lifetime parameters cannot have default values
+
 parse_multiple_where_clauses = cannot define duplicate `where` clauses on an item
     .label = previous `where` clause starts here
     .suggestion = consider joining the two `where` clauses into one

compiler/rustc_hir_typeck/src/demand.rs

@@ -60,6 +60,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             || self.suggest_clone_for_ref(err, expr, expr_ty, expected)
             || self.suggest_into(err, expr, expr_ty, expected)
             || self.suggest_floating_point_literal(err, expr, expected)
+            || self.suggest_null_ptr_for_literal_zero_given_to_ptr_arg(err, expr, expected)
             || self.note_result_coercion(err, expr, expected, expr_ty);
         if !suggested {
             self.point_at_expr_source_of_inferred_type(err, expr, expr_ty, expected, expr.span);

compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs

@@ -921,6 +921,22 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 kind: hir::ImplItemKind::Fn(ref sig, ..),
                 ..
             }) => Some((&sig.decl, ident, false)),
+            Node::Expr(&hir::Expr {
+                hir_id,
+                kind: hir::ExprKind::Closure(..),
+                ..
+            }) if let Some(Node::Expr(&hir::Expr {
+                hir_id,
+                kind: hir::ExprKind::Call(..),
+                ..
+            })) = self.tcx.hir().find_parent(hir_id) &&
+            let Some(Node::Item(&hir::Item {
+                ident,
+                kind: hir::ItemKind::Fn(ref sig, ..),
+                ..
+            })) = self.tcx.hir().find_parent(hir_id) => {
+                Some((&sig.decl, ident, ident.name != sym::main))
+            },
             _ => None,
         }
     }

compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs

@@ -13,6 +13,7 @@ use rustc_hir::{
 use rustc_hir_analysis::astconv::AstConv;
 use rustc_infer::traits::{self, StatementAsExpression};
 use rustc_middle::lint::in_external_macro;
+use rustc_middle::ty::print::with_no_trimmed_paths;
 use rustc_middle::ty::{
     self, suggest_constraining_type_params, Binder, DefIdTree, IsSuggestable, ToPredicate, Ty,
     TypeVisitable,
@@ -704,10 +705,38 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 }
             }
             hir::FnRetTy::Return(ty) => {
+                let span = ty.span;
+
+                if let hir::TyKind::OpaqueDef(item_id, ..) = ty.kind
+                && let hir::Node::Item(hir::Item {
+                    kind: hir::ItemKind::OpaqueTy(op_ty),
+                    ..
+                }) = self.tcx.hir().get(item_id.hir_id())
+                && let hir::OpaqueTy {
+                    bounds: [bound], ..
+                } = op_ty
+                && let hir::GenericBound::LangItemTrait(
+                    hir::LangItem::Future, _, _, generic_args) = bound
+                && let hir::GenericArgs { bindings: [ty_binding], .. } = generic_args
+                && let hir::TypeBinding { kind, .. } = ty_binding
+                && let hir::TypeBindingKind::Equality { term } = kind
+                && let hir::Term::Ty(term_ty) = term {
+                    // Check if async function's return type was omitted.
+                    // Don't emit suggestions if the found type is `impl Future<...>`.
+                    debug!("suggest_missing_return_type: found = {:?}", found);
+                    if found.is_suggestable(self.tcx, false) {
+                        if term_ty.span.is_empty() {
+                            err.subdiagnostic(AddReturnTypeSuggestion::Add { span, found: found.to_string() });
+                            return true;
+                        } else {
+                            err.subdiagnostic(ExpectedReturnTypeLabel::Other { span, expected });
+                        }
+                    }
+                }
+
                 // Only point to return type if the expected type is the return type, as if they
                 // are not, the expectation must have been caused by something else.
                 debug!("suggest_missing_return_type: return type {:?} node {:?}", ty, ty.kind);
-                let span = ty.span;
                 let ty = self.astconv().ast_ty_to_ty(ty);
                 debug!("suggest_missing_return_type: return type {:?}", ty);
                 debug!("suggest_missing_return_type: expected type {:?}", ty);
@@ -1244,6 +1273,49 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         }
     }
 
+    /// Suggest providing `std::ptr::null()` or `std::ptr::null_mut()` if they
+    /// pass in a literal 0 to an raw pointer.
+    #[instrument(skip(self, err))]
+    pub(crate) fn suggest_null_ptr_for_literal_zero_given_to_ptr_arg(
+        &self,
+        err: &mut Diagnostic,
+        expr: &hir::Expr<'_>,
+        expected_ty: Ty<'tcx>,
+    ) -> bool {
+        // Expected type needs to be a raw pointer.
+        let ty::RawPtr(ty::TypeAndMut { mutbl, .. }) = expected_ty.kind() else {
+            return false;
+        };
+
+        // Provided expression needs to be a literal `0`.
+        let ExprKind::Lit(Spanned {
+            node: rustc_ast::LitKind::Int(0, _),
+            span,
+        }) = expr.kind else {
+            return false;
+        };
+
+        // We need to find a null pointer symbol to suggest
+        let null_sym = match mutbl {
+            hir::Mutability::Not => sym::ptr_null,
+            hir::Mutability::Mut => sym::ptr_null_mut,
+        };
+        let Some(null_did) = self.tcx.get_diagnostic_item(null_sym) else {
+            return false;
+        };
+        let null_path_str = with_no_trimmed_paths!(self.tcx.def_path_str(null_did));
+
+        // We have satisfied all requirements to provide a suggestion. Emit it.
+        err.span_suggestion(
+            span,
+            format!("if you meant to create a null pointer, use `{null_path_str}()`"),
+            null_path_str + "()",
+            Applicability::MachineApplicable,
+        );
+
+        true
+    }
+
     pub(crate) fn suggest_associated_const(
         &self,
         err: &mut Diagnostic,

compiler/rustc_mir_dataflow/src/value_analysis.rs

@@ -790,7 +790,7 @@ impl<V, T> TryFrom<ProjectionElem<V, T>> for TrackElem {
 }
 
 /// Invokes `f` on all direct fields of `ty`.
-fn iter_fields<'tcx>(
+pub fn iter_fields<'tcx>(
     ty: Ty<'tcx>,
     tcx: TyCtxt<'tcx>,
     mut f: impl FnMut(Option<VariantIdx>, Field, Ty<'tcx>),
@@ -824,7 +824,7 @@ fn iter_fields<'tcx>(
 }
 
 /// Returns all locals with projections that have their reference or address taken.
-fn excluded_locals(body: &Body<'_>) -> IndexVec<Local, bool> {
+pub fn excluded_locals(body: &Body<'_>) -> IndexVec<Local, bool> {
     struct Collector {
         result: IndexVec<Local, bool>,
     }