Added comments

Author: spirali

compiler/rustc_next_trait_solver/src/solve/assembly/mod.rs

@@ -1261,6 +1261,10 @@ where
     D: SolverDelegate<Interner = I>,
     I: Interner,
 {
+    // - `Continue(())`: no generic parameter was found, the type is global
+    // - `Break(Ok(Certainty::Yes))`: a generic parameter was found, the type is non-global
+    // - `Break(Ok(Certainty::Maybe(_)))`: the recursion limit reached, assume that the type is non-global
+    // - `Break(Err(NoSolution))`: normalization failed
     type Result = ControlFlow<Result<Certainty, NoSolution>>;
 
     fn visit_binder<T: TypeVisitable<I>>(&mut self, t: &ty::Binder<I, T>) -> Self::Result {

tests/ui/traits/next-solver/find-param-recursion-issue-152716.rs

@@ -1,6 +1,10 @@
 //@ compile-flags: -Znext-solver
 
 // Regression test for <https://github.com/rust-lang/rust/issues/152716>.
+//
+// This test checks that we hit the recursion limit for recursively defined projections.
+// Normalization of `<T as Proj<'b>>::Assoc` could introduce the same projection again.
+// Previously, we get into an infinite recursion.
 
 trait Trait<T> {}
 trait Proj<'a> {