Rollup merge of #134279 - jieyouxu:return-adjustment-target, r=compil…

…er-errors

(Re-)return adjustment target if adjust kind is never-to-any

This PR fixes #134162 where we ICE'd on

```rs
fn main() {
    struct X;
    let _ = [X] == [panic!(); 2];
}
```

In #121208 (comment), there was a change

```diff
- if let Some(adjustments) = self.typeck_results.borrow().adjustments().get(expr.hir_id) {
-     let reported = self.dcx().span_delayed_bug(
-         expr.span,
-         "expression with never type wound up being adjusted",
-     );
-     return if let [Adjustment { kind: Adjust::NeverToAny, target }] = &adjustments[..] {
-         target.to_owned()
-     } else {
-         Ty::new_error(self.tcx(), reported)
-     };
- }
+ if let Some(_) = self.typeck_results.borrow().adjustments().get(expr.hir_id) {
+     self.dcx()
+         .span_bug(expr.span, "expression with never type wound up being adjusted");
+ }
```

It turned out returning the adjustment target if the adjustment kind is `NeverToAny` is necessary, as otherwise we will go through a series of `delay_bug`s and eventually find that we constructed a `TyKind::Error` without having actually emitted an error.

This PR addresses that by re-returning the adjustment target if the adjustment kind is `NeverToAny`, partially reverting this change from #121208.

This PR has two commits:

1. The first commit adds a regression test for #134162, which will ICE (on stable 1.83.0, beta and nightly 2024-12-13).
2. The second commit is the partial revert, which will fix the ICE.

cc `@nnethercote` FYI as this is related to #121208 changes. The changes from #121208 exposed that we lacked test coverage for the code pattern reported in #134162.

compiler/rustc_hir_typeck/src/expr.rs

@@ -72,12 +72,17 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         if self.try_structurally_resolve_type(expr.span, ty).is_never()
             && self.expr_guaranteed_to_constitute_read_for_never(expr)
         {
-            if let Some(_) = self.typeck_results.borrow().adjustments().get(expr.hir_id) {
+            if let Some(adjustments) = self.typeck_results.borrow().adjustments().get(expr.hir_id) {
                 let reported = self.dcx().span_delayed_bug(
                     expr.span,
                     "expression with never type wound up being adjusted",
                 );
-                return Ty::new_error(self.tcx(), reported);
+
+                return if let [Adjustment { kind: Adjust::NeverToAny, target }] = &adjustments[..] {
+                    target.to_owned()
+                } else {
+                    Ty::new_error(self.tcx(), reported)
+                };
             }
 
             let adj_ty = self.next_ty_var(expr.span);

tests/ui/typeck/rhs-ty-hint-134162.e2018.stderr

@@ -0,0 +1,11 @@
+error[E0369]: binary operation `==` cannot be applied to type `[X; 1]`
+  --> $DIR/rhs-ty-hint-134162.rs:16:17
+   |
+LL |     let _ = [X] == [panic!(); 2];
+   |             --- ^^ ------------- [_; 2]
+   |             |
+   |             [X; 1]
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0369`.

tests/ui/typeck/rhs-ty-hint-134162.e2021.stderr

@@ -0,0 +1,11 @@
+error[E0369]: binary operation `==` cannot be applied to type `[X; 1]`
+  --> $DIR/rhs-ty-hint-134162.rs:16:17
+   |
+LL |     let _ = [X] == [panic!(); 2];
+   |             --- ^^ ------------- [_; 2]
+   |             |
+   |             [X; 1]
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0369`.

tests/ui/typeck/rhs-ty-hint-134162.e2024.stderr

@@ -0,0 +1,11 @@
+error[E0369]: binary operation `==` cannot be applied to type `[X; 1]`
+  --> $DIR/rhs-ty-hint-134162.rs:16:17
+   |
+LL |     let _ = [X] == [panic!(); 2];
+   |             --- ^^ ------------- [_; 2]
+   |             |
+   |             [X; 1]
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0369`.

tests/ui/typeck/rhs-ty-hint-134162.rs

@@ -0,0 +1,18 @@
+//! Regression test for <https://github.com/rust-lang/rust/issues/134162>.
+//!
+//! <https://github.com/rust-lang/rust/pull/110877> introduced RHS type hints for when a ty doesn't
+//! support a bin op. In the suggestion path, there was a `delay_bug`.
+//! <https://github.com/rust-lang/rust/pull/121208> converted this `delay_bug` to `bug`, which did
+//! not trigger any test failures as we did not have test coverage for this particular case. This
+//! manifested in an ICE as reported in <https://github.com/rust-lang/rust/issues/134162>.
+
+//@ revisions: e2018 e2021 e2024
+//@[e2018] edition: 2018
+//@[e2021] edition: 2021
+//@[e2024] edition: 2024
+
+fn main() {
+    struct X;
+    let _ = [X] == [panic!(); 2];
+    //[e2018,e2021,e2024]~^ ERROR binary operation `==` cannot be applied to type `[X; 1]`
+}