Fix ICE on empty file with -Zquery-dep-graph

compiler/rustc_middle/src/dep_graph/graph.rs

@@ -826,7 +826,13 @@ pub(crate) fn register_dep_node_debug_str<F>(&self, dep_node: DepNode, debug_str
     where
         F: FnOnce() -> String,
     {
-        let dep_node_debug = &self.data.as_ref().unwrap().dep_node_debug;
+        // Early queries (e.g., `-Z query-dep-graph` on empty crates) can reach here
+        // before the graph is initialized. Return early to prevent an ICE.
+        let data = match &self.data {
+            Some(d) => d,
+            None => return,
+        };
+        let dep_node_debug = &data.dep_node_debug;
 
         if dep_node_debug.borrow().contains_key(&dep_node) {
             return;

tests/ui/dep-graph/query-dep-graph-empty.rs

@@ -0,0 +1,7 @@
+//@ build-pass
+//@ compile-flags: -Zquery-dep-graph --crate-type lib
+//@ edition: 2021
+
+// This file is intentionally left empty to reproduce issue #153199.
+// rustc used to ICE when generating a dependency graph for an empty file
+// because early queries would panic when unwrapping an uninitialized graph.