Failing test

tests/ui/specialization/anyid-repro-125197.rs

@@ -0,0 +1,17 @@
+//@ aux-build: anyid-repro-125197.rs
+//@ check-pass
+
+// Makes sure that we don't check `specializes(impl1, impl2)` for a pair of impls that don't
+// actually participate in specialization. Since <https://github.com/rust-lang/rust/pull/122791>,
+// we don't treat inductive cycles as errors -- so we may need to winnow more pairs of impls, and
+// we try to winnow impls in favor of other impls. However, if we're *inside* the `specializes`
+// query, then may have a query cycle if we call `specializes` again! 
+
+extern crate anyid_repro_125197;
+use anyid_repro_125197::AnyId;
+
+fn main() {
+    let x = "hello, world";
+    let y: AnyId = x.into();
+    let _ = y == x;
+}

tests/ui/specialization/auxiliary/anyid-repro-125197.rs

@@ -0,0 +1,26 @@
+use std::fmt::Display;
+use std::sync::Arc;
+
+pub struct AnyId(());
+
+impl PartialEq<Self> for AnyId {
+    fn eq(&self, _: &Self) -> bool {
+        todo!()
+    }
+}
+
+impl<T: Identifier> PartialEq<T> for AnyId {
+    fn eq(&self, _: &T) -> bool {
+        todo!()
+    }
+}
+
+impl<T: Identifier> From<T> for AnyId {
+    fn from(_: T) -> Self {
+        todo!()
+    }
+}
+
+pub trait Identifier: Display + 'static {}
+
+impl<T> Identifier for T where T: PartialEq + Display + 'static {}