Revert some span_bugs to span_delayed_bug.

Fixes #121445.
Fixes #121457.

compiler/rustc_hir_analysis/src/check/compare_impl_item/refine.rs

@@ -154,10 +154,8 @@ pub(super) fn check_refining_return_position_impl_trait_in_trait<'tcx>(
         trait_m_sig.inputs_and_output,
     ));
     if !ocx.select_all_or_error().is_empty() {
-        // This code path is not reached in any tests, but may be reachable. If
+        tcx.dcx().delayed_bug("encountered errors when checking RPITIT refinement (selection)");
-        // this is triggered, it should be converted to `delayed_bug` and the
+        return;
-        // triggering case turned into a test.
-        tcx.dcx().bug("encountered errors when checking RPITIT refinement (selection)");
     }
     let outlives_env = OutlivesEnvironment::with_bounds(
         param_env,
@@ -165,10 +163,8 @@ pub(super) fn check_refining_return_position_impl_trait_in_trait<'tcx>(
     );
     let errors = infcx.resolve_regions(&outlives_env);
     if !errors.is_empty() {
-        // This code path is not reached in any tests, but may be reachable. If
+        tcx.dcx().delayed_bug("encountered errors when checking RPITIT refinement (regions)");
-        // this is triggered, it should be converted to `delayed_bug` and the
+        return;
-        // triggering case turned into a test.
-        tcx.dcx().bug("encountered errors when checking RPITIT refinement (regions)");
     }
     // Resolve any lifetime variables that may have been introduced during normalization.
     let Ok((trait_bounds, impl_bounds)) = infcx.fully_resolve((trait_bounds, impl_bounds)) else {

compiler/rustc_hir_typeck/src/expr.rs

@@ -76,9 +76,16 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         // While we don't allow *arbitrary* coercions here, we *do* allow
         // coercions from ! to `expected`.
         if ty.is_never() {
-            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) {
-                self.dcx()
+                let reported = self.dcx().span_delayed_bug(
-                    .span_bug(expr.span, "expression with never type wound up being adjusted");
+                    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)
+                };
             }
 
             let adj_ty = self.next_ty_var(TypeVariableOrigin {

tests/ui/impl-trait/in-trait/span-bug-issue-121457.rs

@@ -0,0 +1,18 @@
+pub trait Iterable {
+    type Item<'a>
+    where
+        Self: 'a;
+
+    fn iter(&self) -> impl Iterator;
+}
+
+impl<'a, I: 'a + Iterable> Iterable for &'a I {
+    type Item = u32;
+    //~^ ERROR lifetime parameters or bounds on type `Item` do not match the trait declaration
+
+    fn iter(&self) -> impl for<'missing> Iterator<Item = Self::Item<'missing>> {}
+    //~^ ERROR binding for associated type `Item` references lifetime `'missing`
+    //~| ERROR `()` is not an iterator
+}
+
+fn main() {}

tests/ui/impl-trait/in-trait/span-bug-issue-121457.stderr

@@ -0,0 +1,30 @@
+error[E0582]: binding for associated type `Item` references lifetime `'missing`, which does not appear in the trait input types
+  --> $DIR/span-bug-issue-121457.rs:13:51
+   |
+LL |     fn iter(&self) -> impl for<'missing> Iterator<Item = Self::Item<'missing>> {}
+   |                                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error[E0195]: lifetime parameters or bounds on type `Item` do not match the trait declaration
+  --> $DIR/span-bug-issue-121457.rs:10:14
+   |
+LL |     type Item<'a>
+   |              ---- lifetimes in impl do not match this type in trait
+LL |     where
+LL |         Self: 'a;
+   |               -- this bound might be missing in the impl
+...
+LL |     type Item = u32;
+   |              ^ lifetimes do not match type in trait
+
+error[E0277]: `()` is not an iterator
+  --> $DIR/span-bug-issue-121457.rs:13:23
+   |
+LL |     fn iter(&self) -> impl for<'missing> Iterator<Item = Self::Item<'missing>> {}
+   |                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `()` is not an iterator
+   |
+   = help: the trait `Iterator` is not implemented for `()`
+
+error: aborting due to 3 previous errors
+
+Some errors have detailed explanations: E0195, E0277, E0582.
+For more information about an error, try `rustc --explain E0195`.

tests/ui/never_type/span-bug-issue-121445.rs

@@ -0,0 +1,15 @@
+#![feature(never_type)]
+
+fn test2() {
+    let x: !;
+    let c2 = SingleVariant::Points(0)
+        | match x { //~ ERROR no implementation for `SingleVariant | ()`
+            _ => (),
+        };
+}
+
+enum SingleVariant {
+    Points(u32),
+}
+
+fn main() {}

tests/ui/never_type/span-bug-issue-121445.stderr

@@ -0,0 +1,22 @@
+error[E0369]: no implementation for `SingleVariant | ()`
+  --> $DIR/span-bug-issue-121445.rs:6:9
+   |
+LL |       let c2 = SingleVariant::Points(0)
+   |                ------------------------ SingleVariant
+LL |           | match x {
+   |  _________^_-
+LL | |             _ => (),
+LL | |         };
+   | |_________- ()
+   |
+note: an implementation of `BitOr<()>` might be missing for `SingleVariant`
+  --> $DIR/span-bug-issue-121445.rs:11:1
+   |
+LL | enum SingleVariant {
+   | ^^^^^^^^^^^^^^^^^^ must implement `BitOr<()>`
+note: the trait `BitOr` must be implemented
+  --> $SRC_DIR/core/src/ops/bit.rs:LL:COL
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0369`.