Fix bugs; fix and add tests

src/librustdoc/clean/utils.rs

@@ -15,7 +15,7 @@ use rustc_hir::def::{DefKind, Res};
 use rustc_hir::def_id::{DefId, LOCAL_CRATE};
 use rustc_middle::mir::interpret::ConstValue;
 use rustc_middle::ty::subst::{GenericArgKind, SubstsRef};
-use rustc_middle::ty::{self, DefIdTree, Ty};
+use rustc_middle::ty::{self, DefIdTree, Ty, TyCtxt};
 use rustc_span::symbol::{kw, sym, Symbol};
 use std::mem;
 
@@ -624,3 +624,25 @@ where
     *cx.impl_trait_bounds.borrow_mut() = old_bounds;
     r
 }
+
+crate fn find_closest_parent_module(tcx: TyCtxt<'_>, def_id: DefId) -> Option<DefId> {
+    let mut current = def_id;
+    // The immediate parent might not always be a module.
+    // Find the first parent which is.
+    loop {
+        if let Some(parent) = tcx.parent(current) {
+            if tcx.def_kind(parent) == DefKind::Mod {
+                break Some(parent);
+            }
+            current = parent;
+        } else {
+            debug!(
+                "{:?} has no parent (kind={:?}, original was {:?})",
+                current,
+                tcx.def_kind(current),
+                def_id
+            );
+            break None;
+        }
+    }
+}