Auto merge of #11596 - blyxyas:fix-fp-needless_pass_by_ref_mut, r=Jarcho

Move `needless_pass_by_ref_mut`: `suspicious` -> `nursery`

[Related to [this Zulip thread](https://rust-lang.zulipchat.com/#narrow/stream/257328-clippy/topic/needless_pass_by_ref_mut.20isn't.20ready.20for.20stable)]

`needless_pass_by_ref_mut` has been released with some important bugs (notably having a lot of reported false positives and an ICE). So it may not be really ready for being in stable until these problems are solved. This PR changes the lint's category from `suspicious` to `nursery`, just that.
changelog: none

clippy_lints/src/needless_pass_by_ref_mut.rs

@@ -49,7 +49,7 @@ declare_clippy_lint! {
     /// ```
     #[clippy::version = "1.72.0"]
     pub NEEDLESS_PASS_BY_REF_MUT,
-    suspicious,
+    nursery,
     "using a `&mut` argument when it's not mutated"
 }
 

tests/ui/infinite_loop.rs

@@ -7,8 +7,6 @@ fn fn_constref(i: &i32) -> i32 {
     unimplemented!()
 }
 fn fn_mutref(i: &mut i32) {
-    //~^ ERROR: this argument is a mutable reference, but not used mutably
-    //~| NOTE: `-D clippy::needless-pass-by-ref-mut` implied by `-D warnings`
     unimplemented!()
 }
 fn fooi() -> i32 {

tests/ui/infinite_loop.stderr

@@ -1,5 +1,5 @@
 error: variables in the condition are not mutated in the loop body
-  --> $DIR/infinite_loop.rs:24:11
+  --> $DIR/infinite_loop.rs:22:11
    |
 LL |     while y < 10 {
    |           ^^^^^^
@@ -8,71 +8,71 @@ LL |     while y < 10 {
    = note: `#[deny(clippy::while_immutable_condition)]` on by default
 
 error: variables in the condition are not mutated in the loop body
-  --> $DIR/infinite_loop.rs:31:11
+  --> $DIR/infinite_loop.rs:29:11
    |
 LL |     while y < 10 && x < 3 {
    |           ^^^^^^^^^^^^^^^
    |
    = note: this may lead to an infinite or to a never running loop
 
 error: variables in the condition are not mutated in the loop body
-  --> $DIR/infinite_loop.rs:40:11
+  --> $DIR/infinite_loop.rs:38:11
    |
 LL |     while !cond {
    |           ^^^^^
    |
    = note: this may lead to an infinite or to a never running loop
 
 error: variables in the condition are not mutated in the loop body
-  --> $DIR/infinite_loop.rs:86:11
+  --> $DIR/infinite_loop.rs:84:11
    |
 LL |     while i < 3 {
    |           ^^^^^
    |
    = note: this may lead to an infinite or to a never running loop
 
 error: variables in the condition are not mutated in the loop body
-  --> $DIR/infinite_loop.rs:93:11
+  --> $DIR/infinite_loop.rs:91:11
    |
 LL |     while i < 3 && j > 0 {
    |           ^^^^^^^^^^^^^^
    |
    = note: this may lead to an infinite or to a never running loop
 
 error: variables in the condition are not mutated in the loop body
-  --> $DIR/infinite_loop.rs:99:11
+  --> $DIR/infinite_loop.rs:97:11
    |
 LL |     while i < 3 {
    |           ^^^^^
    |
    = note: this may lead to an infinite or to a never running loop
 
 error: variables in the condition are not mutated in the loop body
-  --> $DIR/infinite_loop.rs:116:11
+  --> $DIR/infinite_loop.rs:114:11
    |
 LL |     while i < 3 {
    |           ^^^^^
    |
    = note: this may lead to an infinite or to a never running loop
 
 error: variables in the condition are not mutated in the loop body
-  --> $DIR/infinite_loop.rs:123:11
+  --> $DIR/infinite_loop.rs:121:11
    |
 LL |     while i < 3 {
    |           ^^^^^
    |
    = note: this may lead to an infinite or to a never running loop
 
 error: variables in the condition are not mutated in the loop body
-  --> $DIR/infinite_loop.rs:191:15
+  --> $DIR/infinite_loop.rs:189:15
    |
 LL |         while self.count < n {
    |               ^^^^^^^^^^^^^^
    |
    = note: this may lead to an infinite or to a never running loop
 
 error: variables in the condition are not mutated in the loop body
-  --> $DIR/infinite_loop.rs:201:11
+  --> $DIR/infinite_loop.rs:199:11
    |
 LL |     while y < 10 {
    |           ^^^^^^
@@ -82,7 +82,7 @@ LL |     while y < 10 {
    = help: rewrite it as `if cond { loop { } }`
 
 error: variables in the condition are not mutated in the loop body
-  --> $DIR/infinite_loop.rs:210:11
+  --> $DIR/infinite_loop.rs:208:11
    |
 LL |     while y < 10 {
    |           ^^^^^^
@@ -91,14 +91,5 @@ LL |     while y < 10 {
    = note: this loop contains `return`s or `break`s
    = help: rewrite it as `if cond { loop { } }`
 
-error: this argument is a mutable reference, but not used mutably
-  --> $DIR/infinite_loop.rs:9:17
-   |
-LL | fn fn_mutref(i: &mut i32) {
-   |                 ^^^^^^^^ help: consider changing to: `&i32`
-   |
-   = note: `-D clippy::needless-pass-by-ref-mut` implied by `-D warnings`
-   = help: to override `-D warnings` add `#[allow(clippy::needless_pass_by_ref_mut)]`
-
-error: aborting due to 12 previous errors
+error: aborting due to 11 previous errors
 

tests/ui/let_underscore_future.rs

@@ -9,8 +9,6 @@ fn custom() -> impl Future<Output = ()> {
 }
 
 fn do_something_to_future(future: &mut impl Future<Output = ()>) {}
-//~^ ERROR: this argument is a mutable reference, but not used mutably
-//~| NOTE: `-D clippy::needless-pass-by-ref-mut` implied by `-D warnings`
 
 fn main() {
     let _ = some_async_fn();

tests/ui/let_underscore_future.stderr

@@ -1,5 +1,5 @@
 error: non-binding `let` on a future
-  --> $DIR/let_underscore_future.rs:16:5
+  --> $DIR/let_underscore_future.rs:14:5
    |
 LL |     let _ = some_async_fn();
    |     ^^^^^^^^^^^^^^^^^^^^^^^^
@@ -9,29 +9,20 @@ LL |     let _ = some_async_fn();
    = help: to override `-D warnings` add `#[allow(clippy::let_underscore_future)]`
 
 error: non-binding `let` on a future
-  --> $DIR/let_underscore_future.rs:18:5
+  --> $DIR/let_underscore_future.rs:16:5
    |
 LL |     let _ = custom();
    |     ^^^^^^^^^^^^^^^^^
    |
    = help: consider awaiting the future or dropping explicitly with `std::mem::drop`
 
 error: non-binding `let` on a future
-  --> $DIR/let_underscore_future.rs:23:5
+  --> $DIR/let_underscore_future.rs:21:5
    |
 LL |     let _ = future;
    |     ^^^^^^^^^^^^^^^
    |
    = help: consider awaiting the future or dropping explicitly with `std::mem::drop`
 
-error: this argument is a mutable reference, but not used mutably
-  --> $DIR/let_underscore_future.rs:11:35
-   |
-LL | fn do_something_to_future(future: &mut impl Future<Output = ()>) {}
-   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider changing to: `&impl Future<Output = ()>`
-   |
-   = note: `-D clippy::needless-pass-by-ref-mut` implied by `-D warnings`
-   = help: to override `-D warnings` add `#[allow(clippy::needless_pass_by_ref_mut)]`
-
-error: aborting due to 4 previous errors
+error: aborting due to 3 previous errors
 

tests/ui/mut_key.rs

@@ -32,8 +32,6 @@ fn should_not_take_this_arg(m: &mut HashMap<Key, usize>, _n: usize) -> HashSet<K
     //~^ ERROR: mutable key type
     //~| NOTE: `-D clippy::mutable-key-type` implied by `-D warnings`
     //~| ERROR: mutable key type
-    //~| ERROR: this argument is a mutable reference, but not used mutably
-    //~| NOTE: `-D clippy::needless-pass-by-ref-mut` implied by `-D warnings`
     let _other: HashMap<Key, bool> = HashMap::new();
     //~^ ERROR: mutable key type
     m.keys().cloned().collect()

tests/ui/mut_key.stderr

@@ -14,103 +14,94 @@ LL | fn should_not_take_this_arg(m: &mut HashMap<Key, usize>, _n: usize) -> Hash
    |                                                                        ^^^^^^^^^^^^
 
 error: mutable key type
-  --> $DIR/mut_key.rs:37:5
+  --> $DIR/mut_key.rs:35:5
    |
 LL |     let _other: HashMap<Key, bool> = HashMap::new();
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: mutable key type
-  --> $DIR/mut_key.rs:65:22
+  --> $DIR/mut_key.rs:63:22
    |
 LL | fn tuples_bad<U>(_m: &mut HashMap<(Key, U), bool>) {}
    |                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: mutable key type
-  --> $DIR/mut_key.rs:78:5
+  --> $DIR/mut_key.rs:76:5
    |
 LL |     let _map = HashMap::<Cell<usize>, usize>::new();
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: mutable key type
-  --> $DIR/mut_key.rs:80:5
+  --> $DIR/mut_key.rs:78:5
    |
 LL |     let _map = HashMap::<&mut Cell<usize>, usize>::new();
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: mutable key type
-  --> $DIR/mut_key.rs:82:5
+  --> $DIR/mut_key.rs:80:5
    |
 LL |     let _map = HashMap::<&mut usize, usize>::new();
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: mutable key type
-  --> $DIR/mut_key.rs:85:5
+  --> $DIR/mut_key.rs:83:5
    |
 LL |     let _map = HashMap::<Vec<Cell<usize>>, usize>::new();
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: mutable key type
-  --> $DIR/mut_key.rs:87:5
+  --> $DIR/mut_key.rs:85:5
    |
 LL |     let _map = HashMap::<BTreeMap<Cell<usize>, ()>, usize>::new();
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: mutable key type
-  --> $DIR/mut_key.rs:89:5
+  --> $DIR/mut_key.rs:87:5
    |
 LL |     let _map = HashMap::<BTreeMap<(), Cell<usize>>, usize>::new();
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: mutable key type
-  --> $DIR/mut_key.rs:91:5
+  --> $DIR/mut_key.rs:89:5
    |
 LL |     let _map = HashMap::<BTreeSet<Cell<usize>>, usize>::new();
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: mutable key type
-  --> $DIR/mut_key.rs:93:5
+  --> $DIR/mut_key.rs:91:5
    |
 LL |     let _map = HashMap::<Option<Cell<usize>>, usize>::new();
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: mutable key type
-  --> $DIR/mut_key.rs:95:5
+  --> $DIR/mut_key.rs:93:5
    |
 LL |     let _map = HashMap::<Option<Vec<Cell<usize>>>, usize>::new();
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: mutable key type
-  --> $DIR/mut_key.rs:97:5
+  --> $DIR/mut_key.rs:95:5
    |
 LL |     let _map = HashMap::<Result<&mut usize, ()>, usize>::new();
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: mutable key type
-  --> $DIR/mut_key.rs:100:5
+  --> $DIR/mut_key.rs:98:5
    |
 LL |     let _map = HashMap::<Box<Cell<usize>>, usize>::new();
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: mutable key type
-  --> $DIR/mut_key.rs:102:5
+  --> $DIR/mut_key.rs:100:5
    |
 LL |     let _map = HashMap::<Rc<Cell<usize>>, usize>::new();
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: mutable key type
-  --> $DIR/mut_key.rs:104:5
+  --> $DIR/mut_key.rs:102:5
    |
 LL |     let _map = HashMap::<Arc<Cell<usize>>, usize>::new();
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: this argument is a mutable reference, but not used mutably
-  --> $DIR/mut_key.rs:31:32
-   |
-LL | fn should_not_take_this_arg(m: &mut HashMap<Key, usize>, _n: usize) -> HashSet<Key> {
-   |                                ^^^^^^^^^^^^^^^^^^^^^^^^ help: consider changing to: `&HashMap<Key, usize>`
-   |
-   = note: `-D clippy::needless-pass-by-ref-mut` implied by `-D warnings`
-   = help: to override `-D warnings` add `#[allow(clippy::needless_pass_by_ref_mut)]`
-
-error: aborting due to 18 previous errors
+error: aborting due to 17 previous errors
 

tests/ui/mut_reference.rs

@@ -22,8 +22,6 @@ impl MyStruct {
     fn takes_an_immutable_reference(&self, a: &i32) {}
 
     fn takes_a_mutable_reference(&self, a: &mut i32) {}
-    //~^ ERROR: this argument is a mutable reference, but not used mutably
-    //~| NOTE: `-D clippy::needless-pass-by-ref-mut` implied by `-D warnings`
 }
 
 #[warn(clippy::unnecessary_mut_passed)]

tests/ui/mut_reference.stderr

@@ -1,5 +1,5 @@
 error: the function `takes_an_immutable_reference` doesn't need a mutable reference
-  --> $DIR/mut_reference.rs:32:34
+  --> $DIR/mut_reference.rs:30:34
    |
 LL |     takes_an_immutable_reference(&mut 42);
    |                                  ^^^^^^^
@@ -8,25 +8,16 @@ LL |     takes_an_immutable_reference(&mut 42);
    = help: to override `-D warnings` add `#[allow(clippy::unnecessary_mut_passed)]`
 
 error: the function `as_ptr` doesn't need a mutable reference
-  --> $DIR/mut_reference.rs:36:12
+  --> $DIR/mut_reference.rs:34:12
    |
 LL |     as_ptr(&mut 42);
    |            ^^^^^^^
 
 error: the method `takes_an_immutable_reference` doesn't need a mutable reference
-  --> $DIR/mut_reference.rs:41:44
+  --> $DIR/mut_reference.rs:39:44
    |
 LL |     my_struct.takes_an_immutable_reference(&mut 42);
    |                                            ^^^^^^^
 
-error: this argument is a mutable reference, but not used mutably
-  --> $DIR/mut_reference.rs:24:44
-   |
-LL |     fn takes_a_mutable_reference(&self, a: &mut i32) {}
-   |                                            ^^^^^^^^ help: consider changing to: `&i32`
-   |
-   = note: `-D clippy::needless-pass-by-ref-mut` implied by `-D warnings`
-   = help: to override `-D warnings` add `#[allow(clippy::needless_pass_by_ref_mut)]`
-
-error: aborting due to 4 previous errors
+error: aborting due to 3 previous errors
 

tests/ui/needless_pass_by_ref_mut.rs

@@ -1,4 +1,5 @@
 #![allow(clippy::if_same_then_else, clippy::no_effect, clippy::redundant_closure_call)]
+#![warn(clippy::needless_pass_by_ref_mut)]
 #![feature(lint_reasons)]
 //@no-rustfix
 use std::ptr::NonNull;