Add regression test for rust-lang#121772

tests/rustdoc/trait-item-info.rs

@@ -0,0 +1,24 @@
+// This is a regression test for <https://github.com/rust-lang/rust/issues/121772>.
+// The goal is to ensure that the item information is always part of the `<summary>`
+// if there is one.
+
+#![crate_name = "foo"]
+#![feature(staged_api)]
+
+#![unstable(feature = "test", issue = "none")]
+
+// @has 'foo/trait.Foo.html'
+
+#[stable(feature = "rust2", since = "2.2.2")]
+pub trait Foo {
+    // @has - '//div[@class="methods"]/span[@class="item-info"]' 'bla'
+    // Should not be in a `<details>` because there is no doc.
+    #[unstable(feature = "bla", reason = "bla", issue = "111")]
+    fn bla() {}
+
+    // @has - '//details[@class="toggle method-toggle"]/summary/span[@class="item-info"]' 'bar'
+    // Should have a `<summary>` in the `<details>` containing the unstable info.
+    /// doc
+    #[unstable(feature = "bar", reason = "bla", issue = "222")]
+    fn bar() {}
+}