Auto merge of #89576 - tom7980:issue-89275-fix, r=estebank

Prevent error reporting from outputting a recursion error if it finds an ambiguous trait impl during suggestions

Closes #89275

This fixes the compiler reporting a recursion error during another already in progress error by trying to make a conversion method suggestion and encounters ambiguous trait implementations that can convert a the original type into a type that can then be recursively converted into itself via another method in the trait.

Updated OverflowError struct to be an enum so I could differentiate between passes - it's no longer a ZST but I don't think that should be a problem as they only generate when there's an error in compiling code anyway

2 files changed, 43 insertions, 0 deletions

diff --git a/src/test/ui/typeck/issue-89275.rs b/src/test/ui/typeck/issue-89275.rs
new file mode 100644
index 00000000000..b91c0017548
--- /dev/null
+++ b/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]
+}
diff --git a/src/test/ui/typeck/issue-89275.stderr b/src/test/ui/typeck/issue-89275.stderr
new file mode 100644
index 00000000000..d73e647d21f
--- /dev/null
+++ b/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`.