Add regression test for rust-lang#112852

Author: GuillaumeGomez

tests/rustdoc-json/impls/issue-112852-dangling-trait-impl-id.rs

@@ -0,0 +1,14 @@
+#![feature(no_core)]
+#![no_core]
+
+// @!has "$.index[*][?(@.name == 'HiddenPubStruct')]"
+// @!has "$.index[*][?(@.inner.impl)]"
+// @has "$.index[*][?(@.name=='PubTrait')]"
+pub trait PubTrait {}
+
+#[doc(hidden)]
+pub mod hidden {
+    pub struct HiddenPubStruct;
+
+    impl crate::PubTrait for HiddenPubStruct {}
+}