uplift clippy::clone_double_ref to rustc

compiler/rustc_codegen_ssa/src/back/link.rs

@@ -573,7 +573,7 @@ fn link_dwarf_object<'a>(
 
     impl<Relocations> ThorinSession<Relocations> {
         fn alloc_mmap(&self, data: Mmap) -> &Mmap {
-            (*self.arena_mmap.alloc(data)).borrow()
+            &*self.arena_mmap.alloc(data)
         }
     }
 
@@ -583,7 +583,7 @@ fn link_dwarf_object<'a>(
         }
 
         fn alloc_relocation(&self, data: Relocations) -> &Relocations {
-            (*self.arena_relocations.alloc(data)).borrow()
+            &*self.arena_relocations.alloc(data)
         }
 
         fn read_input(&self, path: &Path) -> std::io::Result<&[u8]> {

compiler/rustc_lint/messages.ftl

@@ -5,6 +5,9 @@ lint_array_into_iter =
     .use_explicit_into_iter_suggestion =
         or use `IntoIterator::into_iter(..)` instead of `.into_iter()` to explicitly iterate by value
 
+lint_suspicious_double_ref_op =
+    using `.{$call}()` on a double reference, which copies `{$ty}` instead of {$op} the inner type
+
 lint_enum_intrinsics_mem_discriminant =
     the return value of `mem::discriminant` is unspecified when called with a non-enum type
     .note = the argument to `discriminant` should be a reference to an enum, but it was passed a reference to a `{$ty_param}`, which is not an enum.

compiler/rustc_lint/src/lints.rs

@@ -564,6 +564,14 @@ pub struct BuiltinUnexpectedCliConfigValue {
     pub value: Symbol,
 }
 
+#[derive(LintDiagnostic)]
+#[diag(lint_suspicious_double_ref_op)]
+pub struct CloneDoubleRef<'a> {
+    pub call: Symbol,
+    pub ty: Ty<'a>,
+    pub op: &'static str,
+}
+
 // deref_into_dyn_supertrait.rs
 #[derive(LintDiagnostic)]
 #[diag(lint_supertrait_as_deref_target)]

compiler/rustc_lint/src/noop_method_call.rs

@@ -1,10 +1,11 @@
 use crate::context::LintContext;
-use crate::lints::NoopMethodCallDiag;
+use crate::lints::{CloneDoubleRef, NoopMethodCallDiag};
 use crate::LateContext;
 use crate::LateLintPass;
 use rustc_hir::def::DefKind;
 use rustc_hir::{Expr, ExprKind};
 use rustc_middle::ty;
+use rustc_middle::ty::adjustment::Adjust;
 use rustc_span::symbol::sym;
 
 declare_lint! {
@@ -15,7 +16,6 @@ declare_lint! {
     ///
     /// ```rust
     /// # #![allow(unused)]
-    /// #![warn(noop_method_call)]
     /// struct Foo;
     /// let foo = &Foo;
     /// let clone: &Foo = foo.clone();
@@ -31,18 +31,48 @@ declare_lint! {
     /// calling `clone` on a `&T` where `T` does not implement clone, actually doesn't do anything
     /// as references are copy. This lint detects these calls and warns the user about them.
     pub NOOP_METHOD_CALL,
-    Allow,
+    Warn,
     "detects the use of well-known noop methods"
 }
 
-declare_lint_pass!(NoopMethodCall => [NOOP_METHOD_CALL]);
+declare_lint! {
+    /// The `suspicious_double_ref_op` lint checks for usage of `.clone()`/`.borrow()`/`.deref()`
+    /// on an `&&T` when `T: !Deref/Borrow/Clone`, which means the call will copy the inner `&T`,
+    /// instead of performing the operation on the underlying `T` and can be confusing.
+    ///
+    /// ### Example
+    ///
+    /// ```rust
+    /// # #![allow(unused)]
+    /// struct Foo;
+    /// let foo = &&Foo;
+    /// let clone: &Foo = foo.clone();
+    /// ```
+    ///
+    /// {{produces}}
+    ///
+    /// ### Explanation
+    ///
+    /// Since `Foo` doesn't implement `Clone`, running `.clone()` only dereferences the double
+    /// reference, instead of cloning the inner type which should be what was intended.
+    pub SUSPICIOUS_DOUBLE_REF_OP,
+    Warn,
+    "using `clone` on `&&T`"
+}
+
+declare_lint_pass!(NoopMethodCall => [NOOP_METHOD_CALL, SUSPICIOUS_DOUBLE_REF_OP]);
 
 impl<'tcx> LateLintPass<'tcx> for NoopMethodCall {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
         // We only care about method calls.
-        let ExprKind::MethodCall(call, receiver, ..) = &expr.kind else {
-            return
+        let ExprKind::MethodCall(call, receiver, _, call_span) = &expr.kind else {
+            return;
         };
+
+        if call_span.from_expansion() {
+            return;
+        }
+
         // We only care about method calls corresponding to the `Clone`, `Deref` and `Borrow`
         // traits and ignore any other method call.
         let did = match cx.typeck_results().type_dependent_def(expr.hir_id) {
@@ -70,25 +100,40 @@ impl<'tcx> LateLintPass<'tcx> for NoopMethodCall {
         };
         // (Re)check that it implements the noop diagnostic.
         let Some(name) = cx.tcx.get_diagnostic_name(i.def_id()) else { return };
-        if !matches!(
-            name,
-            sym::noop_method_borrow | sym::noop_method_clone | sym::noop_method_deref
-        ) {
-            return;
-        }
+
+        let op = match name {
+            sym::noop_method_borrow => "borrowing",
+            sym::noop_method_clone => "cloning",
+            sym::noop_method_deref => "dereferencing",
+            _ => return,
+        };
+
         let receiver_ty = cx.typeck_results().expr_ty(receiver);
         let expr_ty = cx.typeck_results().expr_ty_adjusted(expr);
-        if receiver_ty != expr_ty {
-            // This lint will only trigger if the receiver type and resulting expression \
-            // type are the same, implying that the method call is unnecessary.
+
+        let arg_adjustments = cx.typeck_results().expr_adjustments(receiver);
+
+        // If there is any user defined auto-deref step, then we don't want to warn.
+        // https://github.com/rust-lang/rust-clippy/issues/9272
+        if arg_adjustments.iter().any(|adj| matches!(adj.kind, Adjust::Deref(Some(_)))) {
             return;
         }
+
         let expr_span = expr.span;
         let span = expr_span.with_lo(receiver.span.hi());
-        cx.emit_spanned_lint(
-            NOOP_METHOD_CALL,
-            span,
-            NoopMethodCallDiag { method: call.ident.name, receiver_ty, label: span },
-        );
+
+        if receiver_ty == expr_ty {
+            cx.emit_spanned_lint(
+                NOOP_METHOD_CALL,
+                span,
+                NoopMethodCallDiag { method: call.ident.name, receiver_ty, label: span },
+            );
+        } else {
+            cx.emit_spanned_lint(
+                SUSPICIOUS_DOUBLE_REF_OP,
+                span,
+                CloneDoubleRef { call: call.ident.name, ty: expr_ty, op },
+            )
+        }
     }
 }

compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs

@@ -39,7 +39,6 @@ use rustc_span::def_id::LocalDefId;
 use rustc_span::symbol::{sym, Ident, Symbol};
 use rustc_span::{BytePos, DesugaringKind, ExpnKind, MacroKind, Span, DUMMY_SP};
 use rustc_target::spec::abi;
-use std::ops::Deref;
 
 use super::method_chain::CollectAllMismatches;
 use super::InferCtxtPrivExt;
@@ -3571,7 +3570,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
             // trait_pred `S: Sum<<Self as Iterator>::Item>` and predicate `i32: Sum<&()>`
             let mut type_diffs = vec![];
 
-            if let ObligationCauseCode::ExprBindingObligation(def_id, _, _, idx) = parent_code.deref()
+            if let ObligationCauseCode::ExprBindingObligation(def_id, _, _, idx) = parent_code
                 && let Some(node_substs) = typeck_results.node_substs_opt(call_hir_id)
                 && let where_clauses = self.tcx.predicates_of(def_id).instantiate(self.tcx, node_substs)
                 && let Some(where_pred) = where_clauses.predicates.get(*idx)

library/alloc/src/str.rs

@@ -89,7 +89,7 @@ macro_rules! specialize_for_lengths {
                 $num => {
                     for s in iter {
                         copy_slice_and_advance!(target, sep_bytes);
-                        let content_bytes = s.borrow().as_ref();
+                        let content_bytes = s.as_ref();
                         copy_slice_and_advance!(target, content_bytes);
                     }
                 },
@@ -98,7 +98,7 @@ macro_rules! specialize_for_lengths {
                 // arbitrary non-zero size fallback
                 for s in iter {
                     copy_slice_and_advance!(target, sep_bytes);
-                    let content_bytes = s.borrow().as_ref();
+                    let content_bytes = s.as_ref();
                     copy_slice_and_advance!(target, content_bytes);
                 }
             }

library/core/benches/iter.rs

@@ -1,4 +1,3 @@
-use core::borrow::Borrow;
 use core::iter::*;
 use core::mem;
 use core::num::Wrapping;
@@ -428,7 +427,7 @@ fn bench_trusted_random_access_chunks(b: &mut Bencher) {
         black_box(&v)
             .iter()
             // this shows that we're not relying on the slice::Iter specialization in Copied
-            .map(|b| *b.borrow())
+            .map(|b| *b)
             .array_chunks::<{ mem::size_of::<u64>() }>()
             .map(|ary| {
                 let d = u64::from_ne_bytes(ary);

library/core/tests/clone.rs

@@ -1,4 +1,5 @@
 #[test]
+#[cfg_attr(not(bootstrap), allow(suspicious_double_ref_op))]
 fn test_borrowed_clone() {
     let x = 5;
     let y: &i32 = &x;

src/librustdoc/html/format.rs

@@ -167,7 +167,7 @@ pub(crate) fn print_generic_bounds<'a, 'tcx: 'a>(
     display_fn(move |f| {
         let mut bounds_dup = FxHashSet::default();
 
-        for (i, bound) in bounds.iter().filter(|b| bounds_dup.insert(b.clone())).enumerate() {
+        for (i, bound) in bounds.iter().filter(|b| bounds_dup.insert(*b)).enumerate() {
             if i > 0 {
                 f.write_str(" + ")?;
             }

src/tools/clippy/clippy_lints/src/declared_lints.rs

@@ -312,7 +312,6 @@ pub(crate) static LINTS: &[&crate::LintInfo] = &[
     crate::methods::CHARS_NEXT_CMP_INFO,
     crate::methods::CLEAR_WITH_DRAIN_INFO,
     crate::methods::CLONED_INSTEAD_OF_COPIED_INFO,
-    crate::methods::CLONE_DOUBLE_REF_INFO,
     crate::methods::CLONE_ON_COPY_INFO,
     crate::methods::CLONE_ON_REF_PTR_INFO,
     crate::methods::COLLAPSIBLE_STR_REPLACE_INFO,

src/tools/clippy/clippy_lints/src/methods/clone_on_copy.rs

@@ -1,15 +1,13 @@
-use clippy_utils::diagnostics::{span_lint_and_sugg, span_lint_and_then};
+use clippy_utils::diagnostics::span_lint_and_sugg;
 use clippy_utils::get_parent_node;
 use clippy_utils::source::snippet_with_context;
-use clippy_utils::sugg;
 use clippy_utils::ty::is_copy;
 use rustc_errors::Applicability;
 use rustc_hir::{BindingAnnotation, ByRef, Expr, ExprKind, MatchSource, Node, PatKind, QPath};
 use rustc_lint::LateContext;
 use rustc_middle::ty::{self, adjustment::Adjust, print::with_forced_trimmed_paths};
 use rustc_span::symbol::{sym, Symbol};
 
-use super::CLONE_DOUBLE_REF;
 use super::CLONE_ON_COPY;
 
 /// Checks for the `CLONE_ON_COPY` lint.
@@ -42,41 +40,7 @@ pub(super) fn check(
 
     let ty = cx.typeck_results().expr_ty(expr);
     if let ty::Ref(_, inner, _) = arg_ty.kind() {
-        if let ty::Ref(_, innermost, _) = inner.kind() {
-            span_lint_and_then(
-                cx,
-                CLONE_DOUBLE_REF,
-                expr.span,
-                &with_forced_trimmed_paths!(format!(
-                    "using `clone` on a double-reference; \
-                    this will copy the reference of type `{ty}` instead of cloning the inner type"
-                )),
-                |diag| {
-                    if let Some(snip) = sugg::Sugg::hir_opt(cx, arg) {
-                        let mut ty = innermost;
-                        let mut n = 0;
-                        while let ty::Ref(_, inner, _) = ty.kind() {
-                            ty = inner;
-                            n += 1;
-                        }
-                        let refs = "&".repeat(n + 1);
-                        let derefs = "*".repeat(n);
-                        let explicit = with_forced_trimmed_paths!(format!("<{refs}{ty}>::clone({snip})"));
-                        diag.span_suggestion(
-                            expr.span,
-                            "try dereferencing it",
-                            with_forced_trimmed_paths!(format!("{refs}({derefs}{}).clone()", snip.deref())),
-                            Applicability::MaybeIncorrect,
-                        );
-                        diag.span_suggestion(
-                            expr.span,
-                            "or try being explicit if you are sure, that you want to clone a reference",
-                            explicit,
-                            Applicability::MaybeIncorrect,
-                        );
-                    }
-                },
-            );
+        if let ty::Ref(..) = inner.kind() {
             return; // don't report clone_on_copy
         }
     }

src/tools/clippy/clippy_lints/src/methods/mod.rs

@@ -984,29 +984,6 @@ declare_clippy_lint! {
     "using 'clone' on a ref-counted pointer"
 }
 
-declare_clippy_lint! {
-    /// ### What it does
-    /// Checks for usage of `.clone()` on an `&&T`.
-    ///
-    /// ### Why is this bad?
-    /// Cloning an `&&T` copies the inner `&T`, instead of
-    /// cloning the underlying `T`.
-    ///
-    /// ### Example
-    /// ```rust
-    /// fn main() {
-    ///     let x = vec![1];
-    ///     let y = &&x;
-    ///     let z = y.clone();
-    ///     println!("{:p} {:p}", *y, z); // prints out the same pointer
-    /// }
-    /// ```
-    #[clippy::version = "pre 1.29.0"]
-    pub CLONE_DOUBLE_REF,
-    correctness,
-    "using `clone` on `&&T`"
-}
-
 declare_clippy_lint! {
     /// ### What it does
     /// Checks for usage of `.to_string()` on an `&&T` where
@@ -3258,7 +3235,6 @@ impl_lint_pass!(Methods => [
     CHARS_LAST_CMP,
     CLONE_ON_COPY,
     CLONE_ON_REF_PTR,
-    CLONE_DOUBLE_REF,
     COLLAPSIBLE_STR_REPLACE,
     ITER_OVEREAGER_CLONED,
     CLONED_INSTEAD_OF_COPIED,

src/tools/clippy/clippy_lints/src/renamed_lints.rs

@@ -30,6 +30,7 @@ pub static RENAMED_LINTS: &[(&str, &str)] = &[
     ("clippy::stutter", "clippy::module_name_repetitions"),
     ("clippy::to_string_in_display", "clippy::recursive_format_impl"),
     ("clippy::zero_width_space", "clippy::invisible_characters"),
+    ("clippy::clone_double_ref", "suspicious_double_ref_op"),
     ("clippy::drop_bounds", "drop_bounds"),
     ("clippy::for_loop_over_option", "for_loops_over_fallibles"),
     ("clippy::for_loop_over_result", "for_loops_over_fallibles"),

src/tools/clippy/tests/ui/explicit_deref_methods.fixed

@@ -2,8 +2,8 @@
 #![warn(clippy::explicit_deref_methods)]
 #![allow(unused_variables)]
 #![allow(
+    noop_method_call,
     clippy::borrow_deref_ref,
-    clippy::clone_double_ref,
     clippy::explicit_auto_deref,
     clippy::needless_borrow,
     clippy::uninlined_format_args

src/tools/clippy/tests/ui/explicit_deref_methods.rs

@@ -2,8 +2,8 @@
 #![warn(clippy::explicit_deref_methods)]
 #![allow(unused_variables)]
 #![allow(
+    noop_method_call,
     clippy::borrow_deref_ref,
-    clippy::clone_double_ref,
     clippy::explicit_auto_deref,
     clippy::needless_borrow,
     clippy::uninlined_format_args

src/tools/clippy/tests/ui/rename.fixed

@@ -36,6 +36,7 @@
 #![allow(enum_intrinsics_non_enums)]
 #![allow(non_fmt_panics)]
 #![allow(named_arguments_used_positionally)]
+#![allow(suspicious_double_ref_op)]
 #![allow(temporary_cstring_as_ptr)]
 #![allow(unknown_lints)]
 #![allow(unused_labels)]
@@ -67,6 +68,7 @@
 #![warn(clippy::module_name_repetitions)]
 #![warn(clippy::recursive_format_impl)]
 #![warn(clippy::invisible_characters)]
+#![warn(suspicious_double_ref_op)]
 #![warn(drop_bounds)]
 #![warn(for_loops_over_fallibles)]
 #![warn(for_loops_over_fallibles)]