Issue 89275 fix and test

Issue 89275 fix and test

Fix librustdoc OverflowError usage

rust tidy run

Issue 89275 fix and test

src/test/ui/typeck/issue-89275.rs

@@ -0,0 +1,29 @@
+#![recursion_limit = "5"] // To reduce noise
+
+//expect mutability error when ambiguous traits are in scope
+//and not an overflow error on the span in the main function.
+
+struct Ratio<T>(T);
+
+pub trait Pow {
+    fn pow(self) -> Self;
+}
+
+impl<'a, T> Pow for &'a Ratio<T>
+where
+    &'a T: Pow,
+{
+    fn pow(self) -> Self {
+        self
+    }
+}
+
+fn downcast<'a, W: ?Sized>() -> &'a W {
+    todo!()
+}
+
+struct Other;
+
+fn main() {
+    let other: &mut Other = downcast();//~ERROR 28:29: 28:39: mismatched types [E0308]
+}

src/test/ui/typeck/issue-89275.stderr

@@ -0,0 +1,14 @@
+error[E0308]: mismatched types
+  --> $DIR/issue-89275.rs:28:29
+   |
+LL |     let other: &mut Other = downcast();
+   |                ----------   ^^^^^^^^^^ types differ in mutability
+   |                |
+   |                expected due to this
+   |
+   = note: expected mutable reference `&mut Other`
+                      found reference `&_`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0308`.