Rollup merge of #110955 - fee1-dead-contrib:sus-operation, r=compiler-errors

uplift `clippy::clone_double_ref` as `suspicious_double_ref_op`

Split from #109842.

r? ``@compiler-errors``

tests/ui/lint/noop-method-call.rs

@@ -19,18 +19,17 @@ fn main() {
     let clone_type_ref = &CloneType(1u32);
     let clone_type_ref_clone: CloneType<u32> = clone_type_ref.clone();
 
-    // Calling clone on a double reference doesn't warn since the method call itself
-    // peels the outer reference off
     let clone_type_ref = &&CloneType(1u32);
     let clone_type_ref_clone: &CloneType<u32> = clone_type_ref.clone();
+    //~^ WARNING using `.clone()` on a double reference, which returns `&CloneType<u32>`
 
     let non_deref_type = &PlainType(1u32);
     let non_deref_type_deref: &PlainType<u32> = non_deref_type.deref();
     //~^ WARNING call to `.deref()` on a reference in this situation does nothing
 
-    // Dereferencing a &&T does not warn since it has collapsed the double reference
     let non_deref_type = &&PlainType(1u32);
     let non_deref_type_deref: &PlainType<u32> = non_deref_type.deref();
+    //~^ WARNING using `.deref()` on a double reference, which returns `&PlainType<u32>`
 
     let non_borrow_type = &PlainType(1u32);
     let non_borrow_type_borrow: &PlainType<u32> = non_borrow_type.borrow();
@@ -41,7 +40,8 @@ fn main() {
     let non_borrow_type_borrow: &PlainType<u32> = non_borrow_type.borrow();
 
     let xs = ["a", "b", "c"];
-    let _v: Vec<&str> = xs.iter().map(|x| x.clone()).collect(); // ok, but could use `*x` instead
+    let _v: Vec<&str> = xs.iter().map(|x| x.clone()).collect(); // could use `*x` instead
+    //~^ WARNING using `.clone()` on a double reference, which returns `&str`
 }
 
 fn generic<T>(non_clone_type: &PlainType<T>) {

tests/ui/lint/noop-method-call.stderr

@@ -11,22 +11,42 @@ note: the lint level is defined here
 LL | #![warn(noop_method_call)]
    |         ^^^^^^^^^^^^^^^^
 
+warning: using `.clone()` on a double reference, which returns `&CloneType<u32>` instead of cloning the inner type
+  --> $DIR/noop-method-call.rs:23:63
+   |
+LL |     let clone_type_ref_clone: &CloneType<u32> = clone_type_ref.clone();
+   |                                                               ^^^^^^^^
+   |
+   = note: `#[warn(suspicious_double_ref_op)]` on by default
+
 warning: call to `.deref()` on a reference in this situation does nothing
-  --> $DIR/noop-method-call.rs:28:63
+  --> $DIR/noop-method-call.rs:27:63
    |
 LL |     let non_deref_type_deref: &PlainType<u32> = non_deref_type.deref();
    |                                                               ^^^^^^^^ unnecessary method call
    |
    = note: the type `&PlainType<u32>` which `deref` is being called on is the same as the type returned from `deref`, so the method call does not do anything and can be removed
 
+warning: using `.deref()` on a double reference, which returns `&PlainType<u32>` instead of dereferencing the inner type
+  --> $DIR/noop-method-call.rs:31:63
+   |
+LL |     let non_deref_type_deref: &PlainType<u32> = non_deref_type.deref();
+   |                                                               ^^^^^^^^
+
 warning: call to `.borrow()` on a reference in this situation does nothing
-  --> $DIR/noop-method-call.rs:36:66
+  --> $DIR/noop-method-call.rs:35:66
    |
 LL |     let non_borrow_type_borrow: &PlainType<u32> = non_borrow_type.borrow();
    |                                                                  ^^^^^^^^^ unnecessary method call
    |
    = note: the type `&PlainType<u32>` which `borrow` is being called on is the same as the type returned from `borrow`, so the method call does not do anything and can be removed
 
+warning: using `.clone()` on a double reference, which returns `&str` instead of cloning the inner type
+  --> $DIR/noop-method-call.rs:43:44
+   |
+LL |     let _v: Vec<&str> = xs.iter().map(|x| x.clone()).collect(); // could use `*x` instead
+   |                                            ^^^^^^^^
+
 warning: call to `.clone()` on a reference in this situation does nothing
   --> $DIR/noop-method-call.rs:48:19
    |
@@ -43,5 +63,5 @@ LL |     non_clone_type.clone();
    |
    = note: the type `&PlainType<u32>` which `clone` is being called on is the same as the type returned from `clone`, so the method call does not do anything and can be removed
 
-warning: 5 warnings emitted
+warning: 8 warnings emitted
 

tests/ui/lint/suspicious-double-ref-op.rs

@@ -0,0 +1,30 @@
+#![feature(lazy_cell)]
+#![deny(suspicious_double_ref_op, noop_method_call)]
+
+pub fn clone_on_double_ref() {
+    let x = vec![1];
+    let y = &&x;
+    let z: &Vec<_> = y.clone();
+    //~^ ERROR using `.clone()` on a double reference, which returns `&Vec<i32>`
+
+    println!("{:p} {:p}", *y, z);
+}
+
+use std::sync::LazyLock;
+
+pub static STRS: LazyLock<&str> = LazyLock::new(|| "First");
+
+// https://github.com/rust-lang/rust-clippy/issues/9272
+fn rust_clippy_issue_9272() {
+    let str = STRS.clone();
+    println!("{str}")
+}
+
+fn check(mut encoded: &[u8]) {
+    let _ = &mut encoded.clone();
+    //~^ ERROR call to `.clone()` on a reference in this situation does nothing
+    let _ = &encoded.clone();
+    //~^ ERROR call to `.clone()` on a reference in this situation does nothing
+}
+
+fn main() {}

tests/ui/lint/suspicious-double-ref-op.stderr

@@ -0,0 +1,35 @@
+error: using `.clone()` on a double reference, which returns `&Vec<i32>` instead of cloning the inner type
+  --> $DIR/suspicious-double-ref-op.rs:7:23
+   |
+LL |     let z: &Vec<_> = y.clone();
+   |                       ^^^^^^^^
+   |
+note: the lint level is defined here
+  --> $DIR/suspicious-double-ref-op.rs:2:9
+   |
+LL | #![deny(suspicious_double_ref_op, noop_method_call)]
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: call to `.clone()` on a reference in this situation does nothing
+  --> $DIR/suspicious-double-ref-op.rs:24:25
+   |
+LL |     let _ = &mut encoded.clone();
+   |                         ^^^^^^^^ unnecessary method call
+   |
+   = note: the type `&[u8]` which `clone` is being called on is the same as the type returned from `clone`, so the method call does not do anything and can be removed
+note: the lint level is defined here
+  --> $DIR/suspicious-double-ref-op.rs:2:35
+   |
+LL | #![deny(suspicious_double_ref_op, noop_method_call)]
+   |                                   ^^^^^^^^^^^^^^^^
+
+error: call to `.clone()` on a reference in this situation does nothing
+  --> $DIR/suspicious-double-ref-op.rs:26:21
+   |
+LL |     let _ = &encoded.clone();
+   |                     ^^^^^^^^ unnecessary method call
+   |
+   = note: the type `&[u8]` which `clone` is being called on is the same as the type returned from `clone`, so the method call does not do anything and can be removed
+
+error: aborting due to 3 previous errors
+