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
@@ -278,13 +285,22 @@ impl<'tcx> Visitor<'tcx> for SpanMapVisitor<'tcx> {
                     let tcx = self.tcx;
                     if let Some(body_id) = hir_enclosing_body_owner(tcx, id) {
                         let typeck_results = tcx.typeck_body(tcx.hir_body_owned_by(body_id).id());
+                        let path_res =
+                            match std::panic::catch_unwind(std::panic::AssertUnwindSafe(|| {
+                                typeck_results.qpath_res(qpath, id)
+                            })) {
+                                Ok(path_res) => path_res,
+                                Err(panic) => std::panic::resume_unwind(panic),
+                            };
                         let path = rustc_hir::Path {
                             // We change the span to not include parens.
                             span: path.ident.span,
-                            res: typeck_results.qpath_res(qpath, id),
+                            res: path_res,
                             segments: &[],
                         };
                         self.handle_path(&path, false);
+                    } else {
+                        eprintln!("can't find a body for {id:?} :(");
                     }
                 } else {
                     self.infer_id(path.hir_id, Some(id), path.ident.span.into());

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,
+        {
+        }
+    }
+}