Rollup merge of #110631 - notriddle:notriddle/impl-trait-cycle, r=GuillaumeGomez

rustdoc: catch and don't blow up on impl Trait cycles

Fixes #110629

An odd feature of Rust is that `Foo` is invalid, but `Bar` is okay:

    type Foo<'a, 'b> = Box<dyn PartialEq<Foo<'a, 'b>>>;
    type Bar<'a, 'b> = impl PartialEq<Bar<'a, 'b>>;

To get it right, track every time rustdoc descends into a type alias, so if it shows up twice, it can be write the path instead of infinitely expanding it.

1 files changed, 19 insertions, 0 deletions

diff --git a/tests/rustdoc/issue-110629-private-type-cycle.rs b/tests/rustdoc/issue-110629-private-type-cycle.rs
new file mode 100644
index 00000000000..a4efbb098f7
--- /dev/null
+++ b/tests/rustdoc/issue-110629-private-type-cycle.rs
@@ -0,0 +1,19 @@
+// compile-flags: --document-private-items
+
+#![feature(type_alias_impl_trait)]
+
+type Bar<'a, 'b> = impl PartialEq<Bar<'a, 'b>> + std::fmt::Debug;
+
+// @has issue_110629_private_type_cycle/type.Bar.html
+// @has - '//pre[@class="rust item-decl"]' \
+//     "pub(crate) type Bar<'a, 'b> = impl PartialEq<Bar<'a, 'b>> + Debug;"
+
+fn bar<'a, 'b>(i: &'a i32) -> Bar<'a, 'b> {
+    i
+}
+
+fn main() {
+    let meh = 42;
+    let muh = 42;
+    assert_eq!(bar(&meh), bar(&muh));
+}