Auto merge of #120136 - matthiaskrgr:rollup-3zzb0z9, r=matthiaskrgr

Rollup of 9 pull requests

Successful merges:

 - #117561 (Stabilize `slice_first_last_chunk`)
 - #117662 ([rustdoc] Allows links in headings)
 - #119815 (Format sources into the error message when loading codegen backends)
 - #119835 (Exhaustiveness: simplify empty pattern logic)
 - #119984 (Change return type of unstable `Waker::noop()` from `Waker` to `&Waker`.)
 - #120009 (never_patterns: typecheck never patterns)
 - #120122 (Don't add needs-triage to A-diagnostics)
 - #120126 (Suggest `.swap()` when encountering conflicting borrows from `mem::swap` on a slice)
 - #120134 (Restrict access to the private field of newtype indexes)

Failed merges:

 - #119968 (Remove unused/unnecessary features)

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

15 files changed, 235 insertions, 106 deletions

diff --git a/tests/ui/async-await/for-await-passthrough.rs b/tests/ui/async-await/for-await-passthrough.rs
index 7fa133aaedc..b1a382958a1 100644
--- a/tests/ui/async-await/for-await-passthrough.rs
+++ b/tests/ui/async-await/for-await-passthrough.rs
@@ -25,8 +25,7 @@ async fn real_main() {
 
 fn main() {
     let future = real_main();
-    let waker = std::task::Waker::noop();
-    let mut cx = &mut core::task::Context::from_waker(&waker);
+    let mut cx = &mut core::task::Context::from_waker(std::task::Waker::noop());
     let mut future = core::pin::pin!(future);
     while let core::task::Poll::Pending = future.as_mut().poll(&mut cx) {}
 }
diff --git a/tests/ui/async-await/for-await.rs b/tests/ui/async-await/for-await.rs
index 6345ceb0c27..00dbdfb2389 100644
--- a/tests/ui/async-await/for-await.rs
+++ b/tests/ui/async-await/for-await.rs
@@ -17,8 +17,7 @@ async fn real_main() {
 
 fn main() {
     let future = real_main();
-    let waker = std::task::Waker::noop();
-    let mut cx = &mut core::task::Context::from_waker(&waker);
+    let mut cx = &mut core::task::Context::from_waker(std::task::Waker::noop());
     let mut future = core::pin::pin!(future);
     while let core::task::Poll::Pending = future.as_mut().poll(&mut cx) {}
 }
diff --git a/tests/ui/async-await/in-trait/async-default-fn-overridden.rs b/tests/ui/async-await/in-trait/async-default-fn-overridden.rs
index 491dfcc6ae0..8c01f1bddef 100644
--- a/tests/ui/async-await/in-trait/async-default-fn-overridden.rs
+++ b/tests/ui/async-await/in-trait/async-default-fn-overridden.rs
@@ -40,8 +40,7 @@ fn main() {
     let mut fut = pin!(async_main());
 
     // Poll loop, just to test the future...
-    let waker = Waker::noop();
-    let ctx = &mut Context::from_waker(&waker);
+    let ctx = &mut Context::from_waker(Waker::noop());
 
     loop {
         match fut.as_mut().poll(ctx) {
diff --git a/tests/ui/async-await/in-trait/dont-project-to-specializable-projection.rs b/tests/ui/async-await/in-trait/dont-project-to-specializable-projection.rs
index f21abf012ba..e2fd9f9dfea 100644
--- a/tests/ui/async-await/in-trait/dont-project-to-specializable-projection.rs
+++ b/tests/ui/async-await/in-trait/dont-project-to-specializable-projection.rs
@@ -43,8 +43,7 @@ fn main() {
     let mut fut = pin!(async_main());
 
     // Poll loop, just to test the future...
-    let waker = Waker::noop();
-    let ctx = &mut Context::from_waker(&waker);
+    let ctx = &mut Context::from_waker(Waker::noop());
 
     loop {
         match fut.as_mut().poll(ctx) {
diff --git a/tests/ui/async-await/in-trait/dont-project-to-specializable-projection.stderr b/tests/ui/async-await/in-trait/dont-project-to-specializable-projection.stderr
index 0560cd9c5fe..b7336485eb8 100644
--- a/tests/ui/async-await/in-trait/dont-project-to-specializable-projection.stderr
+++ b/tests/ui/async-await/in-trait/dont-project-to-specializable-projection.stderr
@@ -21,7 +21,7 @@ LL |     default async fn foo(_: T) -> &'static str {
    = note: specialization behaves in inconsistent and surprising ways with async functions in traits, and for now is disallowed
 
 error[E0599]: no method named `poll` found for struct `Pin<&mut impl Future<Output = ()>>` in the current scope
-  --> $DIR/dont-project-to-specializable-projection.rs:50:28
+  --> $DIR/dont-project-to-specializable-projection.rs:49:28
    |
 LL |         match fut.as_mut().poll(ctx) {
    |                            ^^^^ method not found in `Pin<&mut impl Future<Output = ()>>`
diff --git a/tests/ui/coroutine/async-gen-yield-ty-is-unit.rs b/tests/ui/coroutine/async-gen-yield-ty-is-unit.rs
index aac74d3eacb..80c0b69a6f7 100644
--- a/tests/ui/coroutine/async-gen-yield-ty-is-unit.rs
+++ b/tests/ui/coroutine/async-gen-yield-ty-is-unit.rs
@@ -11,7 +11,6 @@ async gen fn gen_fn() -> &'static str {
 
 pub fn main() {
     let async_iterator = pin!(gen_fn());
-    let waker = Waker::noop();
-    let ctx = &mut Context::from_waker(&waker);
+    let ctx = &mut Context::from_waker(Waker::noop());
     async_iterator.poll_next(ctx);
 }
diff --git a/tests/ui/coroutine/async_gen_fn_iter.rs b/tests/ui/coroutine/async_gen_fn_iter.rs
index ec6464d0048..604156b4d37 100644
--- a/tests/ui/coroutine/async_gen_fn_iter.rs
+++ b/tests/ui/coroutine/async_gen_fn_iter.rs
@@ -74,8 +74,7 @@ fn main() {
     let mut fut = pin!(async_main());
 
     // Poll loop, just to test the future...
-    let waker = Waker::noop();
-    let ctx = &mut Context::from_waker(&waker);
+    let ctx = &mut Context::from_waker(Waker::noop());
 
     loop {
         match fut.as_mut().poll(ctx) {
diff --git a/tests/ui/dyn-star/dispatch-on-pin-mut.rs b/tests/ui/dyn-star/dispatch-on-pin-mut.rs
index c4ae279e6c1..151aa9092fb 100644
--- a/tests/ui/dyn-star/dispatch-on-pin-mut.rs
+++ b/tests/ui/dyn-star/dispatch-on-pin-mut.rs
@@ -19,15 +19,14 @@ async fn async_main() {
 // ------------------------------------------------------------------------- //
 // Implementation Details Below...
 
-use std::task::*;
 use std::pin::pin;
+use std::task::*;
 
 fn main() {
     let mut fut = pin!(async_main());
 
     // Poll loop, just to test the future...
-    let waker = Waker::noop();
-    let ctx = &mut Context::from_waker(&waker);
+    let ctx = &mut Context::from_waker(Waker::noop());
 
     loop {
         match fut.as_mut().poll(ctx) {
diff --git a/tests/ui/pattern/never_patterns.rs b/tests/ui/pattern/never_patterns.rs
deleted file mode 100644
index 8f44f8a6559..00000000000
--- a/tests/ui/pattern/never_patterns.rs
+++ /dev/null
@@ -1,73 +0,0 @@
-#![feature(never_patterns)]
-#![allow(incomplete_features)]
-
-enum Void {}
-
-fn main() {}
-
-// The classic use for empty types.
-fn safe_unwrap_result<T>(res: Result<T, Void>) {
-    let Ok(_x) = res; //~ ERROR refutable pattern in local binding
-    let (Ok(_x) | Err(!)) = &res;
-    let (Ok(_x) | Err(&!)) = res.as_ref();
-}
-
-// Check we only accept `!` where we want to.
-fn never_pattern_location(void: Void) {
-    // FIXME(never_patterns): Don't accept on a non-empty type.
-    match Some(0) {
-        None => {}
-        Some(!),
-    }
-    // FIXME(never_patterns): Don't accept on an arbitrary type, even if there are no more branches.
-    match () {
-        () => {}
-        !,
-    }
-    // FIXME(never_patterns): Don't accept even on an empty branch.
-    match None::<Void> {
-        None => {}
-        !,
-    }
-    // FIXME(never_patterns): Let alone if the emptiness is behind a reference.
-    match None::<&Void> {
-        None => {}
-        !,
-    }
-    // Participate in match ergonomics.
-    match &void {
-        !
-    }
-    match &&void {
-        !
-    }
-    match &&void {
-        &!
-    }
-    match &None::<Void> {
-        None => {}
-        Some(!)
-    }
-    match None::<&Void> {
-        None => {}
-        Some(!),
-    }
-    // Accept on a composite empty type.
-    match None::<&(u32, Void)> {
-        None => {}
-        Some(&!),
-    }
-    // Accept on an simple empty type.
-    match None::<Void> {
-        None => {}
-        Some(!),
-    }
-    match None::<&Void> {
-        None => {}
-        Some(&!),
-    }
-    match None::<&(u32, Void)> {
-        None => {}
-        Some(&(_, !)),
-    }
-}
diff --git a/tests/ui/pattern/never_patterns.stderr b/tests/ui/pattern/never_patterns.stderr
deleted file mode 100644
index 20eeb01cf71..00000000000
--- a/tests/ui/pattern/never_patterns.stderr
+++ /dev/null
@@ -1,17 +0,0 @@
-error[E0005]: refutable pattern in local binding
-  --> $DIR/never_patterns.rs:10:9
-   |
-LL |     let Ok(_x) = res;
-   |         ^^^^^^ pattern `Err(_)` not covered
-   |
-   = note: `let` bindings require an "irrefutable pattern", like a `struct` or an `enum` with only one variant
-   = note: for more information, visit https://doc.rust-lang.org/book/ch18-02-refutability.html
-   = note: the matched value is of type `Result<T, Void>`
-help: you might want to use `let else` to handle the variant that isn't matched
-   |
-LL |     let Ok(_x) = res else { todo!() };
-   |                      ++++++++++++++++
-
-error: aborting due to 1 previous error
-
-For more information about this error, try `rustc --explain E0005`.
diff --git a/tests/ui/rfcs/rfc-0000-never_patterns/typeck.fail.stderr b/tests/ui/rfcs/rfc-0000-never_patterns/typeck.fail.stderr
new file mode 100644
index 00000000000..013a8b53a55
--- /dev/null
+++ b/tests/ui/rfcs/rfc-0000-never_patterns/typeck.fail.stderr
@@ -0,0 +1,66 @@
+error: mismatched types
+  --> $DIR/typeck.rs:25:9
+   |
+LL |         !,
+   |         ^ a never pattern must be used on an uninhabited type
+   |
+   = note: the matched value is of type `()`
+
+error: mismatched types
+  --> $DIR/typeck.rs:29:9
+   |
+LL |         !,
+   |         ^ a never pattern must be used on an uninhabited type
+   |
+   = note: the matched value is of type `(i32, bool)`
+
+error: mismatched types
+  --> $DIR/typeck.rs:33:13
+   |
+LL |         (_, !),
+   |             ^ a never pattern must be used on an uninhabited type
+   |
+   = note: the matched value is of type `bool`
+
+error: mismatched types
+  --> $DIR/typeck.rs:38:14
+   |
+LL |         Some(!),
+   |              ^ a never pattern must be used on an uninhabited type
+   |
+   = note: the matched value is of type `i32`
+
+error: mismatched types
+  --> $DIR/typeck.rs:45:9
+   |
+LL |         !,
+   |         ^ a never pattern must be used on an uninhabited type
+   |
+   = note: the matched value is of type `()`
+
+error: mismatched types
+  --> $DIR/typeck.rs:52:9
+   |
+LL |         !,
+   |         ^ a never pattern must be used on an uninhabited type
+   |
+   = note: the matched value is of type `Option<Void>`
+
+error: mismatched types
+  --> $DIR/typeck.rs:57:9
+   |
+LL |         !,
+   |         ^ a never pattern must be used on an uninhabited type
+   |
+   = note: the matched value is of type `[Void]`
+
+error: mismatched types
+  --> $DIR/typeck.rs:63:9
+   |
+LL |         !,
+   |         ^ a never pattern must be used on an uninhabited type
+   |
+   = note: the matched value is of type `Option<&Void>`
+
+error: aborting due to 8 previous errors
+
diff --git a/tests/ui/rfcs/rfc-0000-never_patterns/typeck.rs b/tests/ui/rfcs/rfc-0000-never_patterns/typeck.rs
new file mode 100644
index 00000000000..31a23fa002c
--- /dev/null
+++ b/tests/ui/rfcs/rfc-0000-never_patterns/typeck.rs
@@ -0,0 +1,125 @@
+// revisions: pass fail
+//[pass] check-pass
+//[fail] check-fail
+#![feature(never_patterns)]
+#![feature(exhaustive_patterns)]
+#![allow(incomplete_features)]
+
+#[derive(Copy, Clone)]
+enum Void {}
+
+fn main() {}
+
+// The classic use for empty types.
+fn safe_unwrap_result<T: Copy>(res: Result<T, Void>) {
+    let Ok(_x) = res;
+    let (Ok(_x) | Err(!)) = &res;
+    let (Ok(_x) | Err(!)) = res.as_ref();
+}
+
+// Check we only accept `!` where we want to.
+#[cfg(fail)]
+fn never_pattern_typeck_fail(void: Void) {
+    // Don't accept on a non-empty type.
+    match () {
+        !,
+        //[fail]~^ ERROR: mismatched types
+    }
+    match (0, false) {
+        !,
+        //[fail]~^ ERROR: mismatched types
+    }
+    match (0, false) {
+        (_, !),
+        //[fail]~^ ERROR: mismatched types
+    }
+    match Some(0) {
+        None => {}
+        Some(!),
+        //[fail]~^ ERROR: mismatched types
+    }
+
+    // Don't accept on an arbitrary type, even if there are no more branches.
+    match () {
+        () => {}
+        !,
+        //[fail]~^ ERROR: mismatched types
+    }
+
+    // Don't accept even on an empty branch.
+    match None::<Void> {
+        None => {}
+        !,
+        //[fail]~^ ERROR: mismatched types
+    }
+    match (&[] as &[Void]) {
+        [] => {}
+        !,
+        //[fail]~^ ERROR: mismatched types
+    }
+    // Let alone if the emptiness is behind a reference.
+    match None::<&Void> {
+        None => {}
+        !,
+        //[fail]~^ ERROR: mismatched types
+    }
+}
+
+#[cfg(pass)]
+fn never_pattern_typeck_pass(void: Void) {
+    // Participate in match ergonomics.
+    match &void {
+        !,
+    }
+    match &&void {
+        !,
+    }
+    match &&void {
+        &!,
+    }
+    match &None::<Void> {
+        None => {}
+        Some(!),
+    }
+    match None::<&Void> {
+        None => {}
+        Some(!),
+    }
+
+    // Accept on a directly empty type.
+    match void {
+        !,
+    }
+    match &void {
+        &!,
+    }
+    match None::<Void> {
+        None => {}
+        Some(!),
+    }
+    match None::<&Void> {
+        None => {}
+        Some(&!),
+    }
+    match None::<&(u32, Void)> {
+        None => {}
+        Some(&(_, !)),
+    }
+    match (&[] as &[Void]) {
+        [] => {}
+        [!],
+    }
+    // Accept on a composite empty type.
+    match None::<&(u32, Void)> {
+        None => {}
+        Some(&!),
+    }
+    match None::<&(u32, Void)> {
+        None => {}
+        Some(!),
+    }
+    match None::<&Result<Void, Void>> {
+        None => {}
+        Some(!),
+    }
+}
diff --git a/tests/ui/suggestions/suggest-slice-swap.fixed b/tests/ui/suggestions/suggest-slice-swap.fixed
new file mode 100644
index 00000000000..05b7ec26379
--- /dev/null
+++ b/tests/ui/suggestions/suggest-slice-swap.fixed
@@ -0,0 +1,9 @@
+// run-rustfix
+#![allow(dead_code)]
+
+fn swap(arr: &mut [u32; 2]) {
+    arr.swap(1, 0);
+    //~^ ERROR cannot borrow `arr[_]` as mutable more than once at a time
+}
+
+fn main() {}
diff --git a/tests/ui/suggestions/suggest-slice-swap.rs b/tests/ui/suggestions/suggest-slice-swap.rs
new file mode 100644
index 00000000000..9f3659aac16
--- /dev/null
+++ b/tests/ui/suggestions/suggest-slice-swap.rs
@@ -0,0 +1,9 @@
+// run-rustfix
+#![allow(dead_code)]
+
+fn swap(arr: &mut [u32; 2]) {
+    std::mem::swap(&mut arr[0], &mut arr[1]);
+    //~^ ERROR cannot borrow `arr[_]` as mutable more than once at a time
+}
+
+fn main() {}
diff --git a/tests/ui/suggestions/suggest-slice-swap.stderr b/tests/ui/suggestions/suggest-slice-swap.stderr
new file mode 100644
index 00000000000..2840fc0a761
--- /dev/null
+++ b/tests/ui/suggestions/suggest-slice-swap.stderr
@@ -0,0 +1,17 @@
+error[E0499]: cannot borrow `arr[_]` as mutable more than once at a time
+  --> $DIR/suggest-slice-swap.rs:5:33
+   |
+LL |     std::mem::swap(&mut arr[0], &mut arr[1]);
+   |     -------------- -----------  ^^^^^^^^^^^ second mutable borrow occurs here
+   |     |              |
+   |     |              first mutable borrow occurs here
+   |     first borrow later used by call
+   |
+help: use `.swap()` to swap elements at the specified indices instead
+   |
+LL |     arr.swap(1, 0);
+   |     ~~~~~~~~~~~~~~
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0499`.