3 files changed, 37 insertions, 9 deletions

diff --git a/crates/hir_def/src/nameres.rs b/crates/hir_def/src/nameres.rs
index 34ff07f3c..f92232eb3 100644
--- a/crates/hir_def/src/nameres.rs
+++ b/crates/hir_def/src/nameres.rs
@@ -337,6 +337,12 @@ impl DefMap {
         None
     }
 
+    /// If this `DefMap` is for a block expression, returns the module containing the block (which
+    /// might again be a block, or a module inside a block).
+    pub fn parent(&self) -> Option<ModuleId> {
+        Some(self.block?.parent)
+    }
+
     // FIXME: this can use some more human-readable format (ideally, an IR
     // even), as this should be a great debugging aid.
     pub fn dump(&self, db: &dyn DefDatabase) -> String {
diff --git a/crates/hir_def/src/nameres/collector.rs b/crates/hir_def/src/nameres/collector.rs
index 6bd41bc08..9996a0807 100644
--- a/crates/hir_def/src/nameres/collector.rs
+++ b/crates/hir_def/src/nameres/collector.rs
@@ -608,7 +608,7 @@ impl DefCollector<'_> {
                                 (
                                     n,
                                     res.filter_visibility(|v| {
-                                        v.is_visible_from_def_map(&self.def_map, module_id)
+                                        v.is_visible_from_def_map(self.db, &self.def_map, module_id)
                                     }),
                                 )
                             })
@@ -761,7 +761,7 @@ impl DefCollector<'_> {
             .filter(|(glob_importing_module, _)| {
                 // we know all resolutions have the same visibility (`vis`), so we
                 // just need to check that once
-                vis.is_visible_from_def_map(&self.def_map, *glob_importing_module)
+                vis.is_visible_from_def_map(self.db, &self.def_map, *glob_importing_module)
             })
             .cloned()
             .collect::<Vec<_>>();
diff --git a/crates/hir_def/src/visibility.rs b/crates/hir_def/src/visibility.rs
index 38da3132b..0e3951910 100644
--- a/crates/hir_def/src/visibility.rs
+++ b/crates/hir_def/src/visibility.rs
@@ -103,7 +103,7 @@ impl Visibility {
             return false;
         }
         let def_map = from_module.def_map(db);
-        self.is_visible_from_def_map(&def_map, from_module.local_id)
+        self.is_visible_from_def_map(db, &def_map, from_module.local_id)
     }
 
     pub(crate) fn is_visible_from_other_crate(self) -> bool {
@@ -115,19 +115,41 @@ impl Visibility {
 
     pub(crate) fn is_visible_from_def_map(
         self,
+        db: &dyn DefDatabase,
         def_map: &DefMap,
-        from_module: crate::LocalModuleId,
+        mut from_module: crate::LocalModuleId,
     ) -> bool {
         let to_module = match self {
             Visibility::Module(m) => m,
             Visibility::Public => return true,
         };
+
         // from_module needs to be a descendant of to_module
-        let mut ancestors = std::iter::successors(Some(from_module), |m| {
-            let parent_id = def_map[*m].parent?;
-            Some(parent_id)
-        });
-        ancestors.any(|m| m == to_module.local_id)
+        let mut def_map = def_map;
+        let mut parent_arc;
+        loop {
+            if def_map.module_id(from_module) == to_module {
+                return true;
+            }
+            match def_map[from_module].parent {
+                Some(parent) => {
+                    from_module = parent;
+                }
+                None => {
+                    match def_map.parent() {
+                        Some(module) => {
+                            parent_arc = module.def_map(db);
+                            def_map = &*parent_arc;
+                            from_module = module.local_id;
+                        }
+                        None => {
+                            // Reached the root module, nothing left to check.
+                            return false;
+                        }
+                    }
+                }
+            }
+        }
     }
 
     /// Returns the most permissive visibility of `self` and `other`.