internal: outline child modules with missing backing file

crates/hir_def/src/nameres/collector.rs

@@ -1743,6 +1743,12 @@ impl ModCollector<'_, '_> {
                         }
                     }
                     Err(candidates) => {
+                        self.push_child_module(
+                            module.name.clone(),
+                            ast_id,
+                            None,
+                            &self.item_tree[module.visibility],
+                        );
                         self.def_collector.def_map.diagnostics.push(
                             DefDiagnostic::unresolved_module(self.module_id, ast_id, candidates),
                         );

crates/hir_def/src/nameres/tests.rs

@@ -375,9 +375,12 @@ pub struct Arc;
 "#,
         expect![[r#"
             crate
+            alloc: t
             alloc_crate: t
             sync: t
 
+            crate::alloc
+
             crate::sync
             Arc: t v
         "#]],
@@ -401,9 +404,12 @@ pub struct Arc;
 "#,
         expect![[r#"
             crate
+            alloc: t
             alloc_crate: t
             sync: t
 
+            crate::alloc
+
             crate::sync
             Arc: t v
         "#]],

crates/hir_def/src/nameres/tests/mod_resolution.rs

@@ -526,6 +526,9 @@ pub struct Baz;
 "#,
         expect![[r#"
             crate
+            foo: t
+
+            crate::foo
         "#]],
     );
 }