Add regression test for #59502

This issue was fixed using a hacky recursion "fuel" argument, but the
issue was never minimized nor was a regression test added. The
underlying bug is still unfixed, so this test should help with fixing it
and removing the `recurse` hack.

src/librustdoc/html/render/search_index.rs

@@ -236,6 +236,7 @@ fn get_index_type_name(clean_type: &clean::Type) -> Option<Symbol> {
 ///
 /// Important note: It goes through generics recursively. So if you have
 /// `T: Option<Result<(), ()>>`, it'll go into `Option` and then into `Result`.
+#[instrument(level = "trace", skip(tcx, res))]
 fn add_generics_and_bounds_as_types<'tcx>(
     generics: &Generics,
     arg: &Type,
@@ -316,6 +317,7 @@ fn add_generics_and_bounds_as_types<'tcx>(
 
     if recurse >= 10 {
         // FIXME: remove this whole recurse thing when the recursion bug is fixed
+        // See #59502 for the original issue.
         return;
     }
 

src/test/rustdoc-ui/search-index-generics-recursion-bug-issue-59502.rs

@@ -0,0 +1,11 @@
+// check-pass
+
+// Minimization of issue #59502
+
+trait MyTrait<T> {
+    type Output;
+}
+
+pub fn pow<T: MyTrait<T, Output = T>>(arg: T) -> T {
+    arg
+}