Add regression test for stripped enum variant fields

Author: GuillaumeGomez

src/test/rustdoc-json/enum_variant_hidden.rs

@@ -0,0 +1,13 @@
+// Regression test for <https://github.com/rust-lang/rust/issues/100529>.
+
+#![no_core]
+#![feature(no_core)]
+
+// @has enum_variant_hidden.json "$.index[*][?(@.name=='ParseError')]"
+// @has - "$.index[*][?(@.name=='UnexpectedEndTag')]"
+// @is - "$.index[*][?(@.name=='UnexpectedEndTag')].inner.variant_kind" '"tuple"'
+// @is - "$.index[*][?(@.name=='UnexpectedEndTag')].inner.variant_inner" []
+
+pub enum ParseError {
+    UnexpectedEndTag(#[doc(hidden)] u32),
+}