Auto merge of rust-lang#128461 - matthiaskrgr:rollup-3dpp11g, r=matthiaskrgr

Rollup of 7 pull requests

Successful merges:

 - rust-lang#123813 (Add `REDUNDANT_IMPORTS` lint for new redundant import detection)
 - rust-lang#126697 ([RFC] mbe: consider the `_` in 2024 an expression)
 - rust-lang#127159 (match lowering: Hide `Candidate` from outside the lowering algorithm)
 - rust-lang#128244 (Peel off explicit (or implicit) deref before suggesting clone on move error in borrowck, remove some hacks)
 - rust-lang#128431 (Add myself as VxWorks target maintainer for reference)
 - rust-lang#128438 (Add special-case for [T, 0] in dropck_outlives)
 - rust-lang#128457 (Fix docs for OnceLock::get_mut_or_init)

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

Author: bors

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -563,11 +563,11 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, '_, 'infcx, 'tcx> {
                 } = move_spans
                     && can_suggest_clone
                 {
-                    self.suggest_cloning(err, ty, expr, None, Some(move_spans));
+                    self.suggest_cloning(err, ty, expr, Some(move_spans));
                 } else if self.suggest_hoisting_call_outside_loop(err, expr) && can_suggest_clone {
                     // The place where the type moves would be misleading to suggest clone.
                     // #121466
-                    self.suggest_cloning(err, ty, expr, None, Some(move_spans));
+                    self.suggest_cloning(err, ty, expr, Some(move_spans));
                 }
             }
 
@@ -1229,8 +1229,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, '_, 'infcx, 'tcx> {
         &self,
         err: &mut Diag<'_>,
         ty: Ty<'tcx>,
-        mut expr: &'tcx hir::Expr<'tcx>,
-        mut other_expr: Option<&'tcx hir::Expr<'tcx>>,
+        expr: &'tcx hir::Expr<'tcx>,
         use_spans: Option<UseSpans<'tcx>>,
     ) {
         if let hir::ExprKind::Struct(_, _, Some(_)) = expr.kind {
@@ -1242,66 +1241,6 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, '_, 'infcx, 'tcx> {
             return;
         }
 
-        if let Some(some_other_expr) = other_expr
-            && let Some(parent_binop) =
-                self.infcx.tcx.hir().parent_iter(expr.hir_id).find_map(|n| {
-                    if let (hir_id, hir::Node::Expr(e)) = n
-                        && let hir::ExprKind::AssignOp(_binop, target, _arg) = e.kind
-                        && target.hir_id == expr.hir_id
-                    {
-                        Some(hir_id)
-                    } else {
-                        None
-                    }
-                })
-            && let Some(other_parent_binop) =
-                self.infcx.tcx.hir().parent_iter(some_other_expr.hir_id).find_map(|n| {
-                    if let (hir_id, hir::Node::Expr(expr)) = n
-                        && let hir::ExprKind::AssignOp(..) = expr.kind
-                    {
-                        Some(hir_id)
-                    } else {
-                        None
-                    }
-                })
-            && parent_binop == other_parent_binop
-        {
-            // Explicitly look for `expr += other_expr;` and avoid suggesting
-            // `expr.clone() += other_expr;`, instead suggesting `expr += other_expr.clone();`.
-            other_expr = Some(expr);
-            expr = some_other_expr;
-        }
-        'outer: {
-            if let ty::Ref(..) = ty.kind() {
-                // We check for either `let binding = foo(expr, other_expr);` or
-                // `foo(expr, other_expr);` and if so we don't suggest an incorrect
-                // `foo(expr, other_expr).clone()`
-                if let Some(other_expr) = other_expr
-                    && let Some(parent_let) =
-                        self.infcx.tcx.hir().parent_iter(expr.hir_id).find_map(|n| {
-                            if let (hir_id, hir::Node::LetStmt(_) | hir::Node::Stmt(_)) = n {
-                                Some(hir_id)
-                            } else {
-                                None
-                            }
-                        })
-                    && let Some(other_parent_let) =
-                        self.infcx.tcx.hir().parent_iter(other_expr.hir_id).find_map(|n| {
-                            if let (hir_id, hir::Node::LetStmt(_) | hir::Node::Stmt(_)) = n {
-                                Some(hir_id)
-                            } else {
-                                None
-                            }
-                        })
-                    && parent_let == other_parent_let
-                {
-                    // Explicitly check that we don't have `foo(&*expr, other_expr)`, as cloning the
-                    // result of `foo(...)` won't help.
-                    break 'outer;
-                }
-            }
-        }
-        let ty = ty.peel_refs();
         if self.implements_clone(ty) {
             self.suggest_cloning_inner(err, ty, expr);
         } else if let ty::Adt(def, args) = ty.kind()
@@ -1573,10 +1512,27 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, '_, 'infcx, 'tcx> {
             );
         self.suggest_copy_for_type_in_cloned_ref(&mut err, place);
         let typeck_results = self.infcx.tcx.typeck(self.mir_def_id());
-        if let Some(expr) = self.find_expr(borrow_span)
-            && let Some(ty) = typeck_results.node_type_opt(expr.hir_id)
-        {
-            self.suggest_cloning(&mut err, ty, expr, self.find_expr(span), Some(move_spans));
+        if let Some(expr) = self.find_expr(borrow_span) {
+            // This is a borrow span, so we want to suggest cloning the referent.
+            if let hir::ExprKind::AddrOf(_, _, borrowed_expr) = expr.kind
+                && let Some(ty) = typeck_results.expr_ty_opt(borrowed_expr)
+            {
+                self.suggest_cloning(&mut err, ty, borrowed_expr, Some(move_spans));
+            } else if typeck_results.expr_adjustments(expr).first().is_some_and(|adj| {
+                matches!(
+                    adj.kind,
+                    ty::adjustment::Adjust::Borrow(ty::adjustment::AutoBorrow::Ref(
+                        _,
+                        ty::adjustment::AutoBorrowMutability::Not
+                            | ty::adjustment::AutoBorrowMutability::Mut {
+                                allow_two_phase_borrow: ty::adjustment::AllowTwoPhase::No
+                            }
+                    ))
+                )
+            }) && let Some(ty) = typeck_results.expr_ty_opt(expr)
+            {
+                self.suggest_cloning(&mut err, ty, expr, Some(move_spans));
+            }
         }
         self.buffer_error(err);
     }

compiler/rustc_borrowck/src/diagnostics/move_errors.rs

@@ -564,9 +564,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, '_, 'infcx, 'tcx> {
 
     fn add_move_hints(&self, error: GroupedMoveError<'tcx>, err: &mut Diag<'_>, span: Span) {
         match error {
-            GroupedMoveError::MovesFromPlace {
-                mut binds_to, move_from, span: other_span, ..
-            } => {
+            GroupedMoveError::MovesFromPlace { mut binds_to, move_from, .. } => {
                 self.add_borrow_suggestions(err, span);
                 if binds_to.is_empty() {
                     let place_ty = move_from.ty(self.body, self.infcx.tcx).ty;
@@ -576,7 +574,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, '_, 'infcx, 'tcx> {
                     };
 
                     if let Some(expr) = self.find_expr(span) {
-                        self.suggest_cloning(err, place_ty, expr, self.find_expr(other_span), None);
+                        self.suggest_cloning(err, place_ty, expr, None);
                     }
 
                     err.subdiagnostic(crate::session_diagnostics::TypeNoCopy::Label {
@@ -608,13 +606,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, '_, 'infcx, 'tcx> {
                 };
 
                 if let Some(expr) = self.find_expr(use_span) {
-                    self.suggest_cloning(
-                        err,
-                        place_ty,
-                        expr,
-                        self.find_expr(span),
-                        Some(use_spans),
-                    );
+                    self.suggest_cloning(err, place_ty, expr, Some(use_spans));
                 }
 
                 err.subdiagnostic(crate::session_diagnostics::TypeNoCopy::Label {
@@ -739,7 +731,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, '_, 'infcx, 'tcx> {
                 let place_desc = &format!("`{}`", self.local_names[*local].unwrap());
 
                 if let Some(expr) = self.find_expr(binding_span) {
-                    self.suggest_cloning(err, bind_to.ty, expr, None, None);
+                    self.suggest_cloning(err, bind_to.ty, expr, None);
                 }
 
                 err.subdiagnostic(crate::session_diagnostics::TypeNoCopy::Label {

compiler/rustc_lint/messages.ftl

@@ -700,10 +700,10 @@ lint_reason_must_be_string_literal = reason must be a string literal
 lint_reason_must_come_last = reason in lint attribute must come last
 
 lint_redundant_import = the item `{$ident}` is imported redundantly
-    .label_imported_here = the item `{ident}` is already imported here
-    .label_defined_here = the item `{ident}` is already defined here
-    .label_imported_prelude = the item `{ident}` is already imported by the extern prelude
-    .label_defined_prelude = the item `{ident}` is already defined by the extern prelude
+    .label_imported_here = the item `{$ident}` is already imported here
+    .label_defined_here = the item `{$ident}` is already defined here
+    .label_imported_prelude = the item `{$ident}` is already imported by the extern prelude
+    .label_defined_prelude = the item `{$ident}` is already defined by the extern prelude
 
 lint_redundant_import_visibility = glob import doesn't reexport anything with visibility `{$import_vis}` because no imported item is public enough
     .note = the most public imported item is `{$max_vis}`

compiler/rustc_lint_defs/src/builtin.rs

@@ -82,6 +82,7 @@ declare_lint_pass! {
         PROC_MACRO_DERIVE_RESOLUTION_FALLBACK,
         PTR_CAST_ADD_AUTO_TO_OBJECT,
         PUB_USE_OF_PRIVATE_EXTERN_CRATE,
+        REDUNDANT_IMPORTS,
         REDUNDANT_LIFETIMES,
         REFINING_IMPL_TRAIT_INTERNAL,
         REFINING_IMPL_TRAIT_REACHABLE,
@@ -426,6 +427,31 @@ declare_lint! {
     "imports that are never used"
 }
 
+declare_lint! {
+    /// The `redundant_imports` lint detects imports that are redundant due to being
+    /// imported already; either through a previous import, or being present in
+    /// the prelude.
+    ///
+    /// ### Example
+    ///
+    /// ```rust,compile_fail
+    /// #![deny(redundant_imports)]
+    /// use std::option::Option::None;
+    /// fn foo() -> Option<i32> { None }
+    /// ```
+    ///
+    /// {{produces}}
+    ///
+    /// ### Explanation
+    ///
+    /// Redundant imports are unnecessary and can be removed to simplify code.
+    /// If you intended to re-export the item to make it available outside of the
+    /// module, add a visibility modifier like `pub`.
+    pub REDUNDANT_IMPORTS,
+    Allow,
+    "imports that are redundant due to being imported already"
+}
+
 declare_lint! {
     /// The `must_not_suspend` lint guards against values that shouldn't be held across suspend points
     /// (`.await`)