Fix ICE in rustdoc when impl is nested in a func

Author: GoldsteinE

src/librustdoc/html/render/span_map.rs

@@ -251,6 +251,13 @@ fn hir_enclosing_body_owner(tcx: TyCtxt<'_>, hir_id: HirId) -> Option<LocalDefId
             return None;
         } else if let Some((def_id, _)) = node.associated_body() {
             return Some(def_id);
+        // Items don't have bodies.
+        // If we go any further, we might encounter an enclosing function
+        // (e.g. if we're inside an impl that's inside of a function).
+        // This would cause us to erroneously consider this function to be the owner
+        // of the node and produce invalid `HirId`s later.
+        } else if matches!(node, Node::Item(_)) {
+            return None;
         }
     }
     None

tests/rustdoc/nested-fn-impl-147882.rs

@@ -0,0 +1,22 @@
+//@ compile-flags: -Zunstable-options --generate-link-to-definition
+
+// See: https://github.com/rust-lang/rust/issues/147882
+
+#![crate_name = "foo"]
+
+trait Fun {
+    fn fun();
+}
+
+trait Other {}
+
+impl Fun for () {
+    fn fun() {
+        impl<E> Other for E
+        where
+            E: std::str::FromStr,
+            E::Err: Send,
+        {
+        }
+    }
+}