add note for `layout_of` when query depth overflows

2 files changed, 36 insertions, 3 deletions

diff --git a/compiler/rustc_query_system/src/query/job.rs b/compiler/rustc_query_system/src/query/job.rs
index 45b4079fb54..a5ea3a098a6 100644
--- a/compiler/rustc_query_system/src/query/job.rs
+++ b/compiler/rustc_query_system/src/query/job.rs
@@ -59,6 +59,7 @@ impl QueryJobId {
     }
 }
 
+#[derive(Clone)]
 pub struct QueryJobInfo {
     pub query: QueryStackFrame,
     pub job: QueryJob,
@@ -116,10 +117,10 @@ impl QueryJob {
     }
 }
 
-#[cfg(not(parallel_compiler))]
 impl QueryJobId {
     #[cold]
     #[inline(never)]
+    #[cfg(not(parallel_compiler))]
     pub(super) fn find_cycle_in_stack(
         &self,
         query_map: QueryMap,
@@ -156,6 +157,27 @@ impl QueryJobId {
 
         panic!("did not find a cycle")
     }
+
+    #[cold]
+    #[inline(never)]
+    pub(super) fn try_find_layout_root(
+        &self,
+        query_map: QueryMap,
+    ) -> Option<(QueryJobInfo, usize)> {
+        let mut last_layout = None;
+        let mut current_id = Some(*self);
+        let mut depth = 0;
+
+        while let Some(id) = current_id {
+            let info = query_map.get(&id).unwrap();
+            if info.query.name == "layout_of" {
+                depth += 1;
+                last_layout = Some((info.clone(), depth));
+            }
+            current_id = info.job.parent;
+        }
+        last_layout
+    }
 }
 
 #[cfg(parallel_compiler)]
diff --git a/compiler/rustc_query_system/src/query/mod.rs b/compiler/rustc_query_system/src/query/mod.rs
index 0b07bb64b6a..e29e8815331 100644
--- a/compiler/rustc_query_system/src/query/mod.rs
+++ b/compiler/rustc_query_system/src/query/mod.rs
@@ -123,7 +123,18 @@ pub trait QueryContext: HasDepContext {
         compute: impl FnOnce() -> R,
     ) -> R;
 
-    fn depth_limit_error(&self) {
-        self.dep_context().sess().emit_fatal(crate::error::QueryOverflow);
+    fn depth_limit_error(&self, job: QueryJobId) {
+        let sess = self.dep_context().sess();
+        let mut layout_of_depth = None;
+        if let Some(map) = self.try_collect_active_jobs() {
+            if let Some((info, depth)) = job.try_find_layout_root(map) {
+                layout_of_depth = Some(crate::error::LayoutOfDepth {
+                    span: info.job.span,
+                    desc: info.query.description,
+                    depth,
+                });
+            }
+        }
+        sess.emit_fatal(crate::error::QueryOverflow { layout_of_depth });
     }
 }