Auto merge of #153690 - nnethercote:find_dep_kind_root, r=petrochenkov

`find_dep_kind_root` tweaks

Two minor changes relating to `find_dep_kind_root`.

r? @SparrowLii

compiler/rustc_query_impl/src/job.rs

@@ -46,7 +46,7 @@ fn latch_of(&self, id: QueryJobId) -> Option<&QueryLatch<'tcx>> {
     }
 }
 
-#[derive(Clone, Debug)]
+#[derive(Debug)]
 pub(crate) struct QueryJobInfo<'tcx> {
     pub(crate) frame: QueryStackFrame<'tcx>,
     pub(crate) job: QueryJob<'tcx>,
@@ -88,27 +88,28 @@ pub(crate) fn find_cycle_in_stack<'tcx>(
     panic!("did not find a cycle")
 }
 
+/// Finds the job closest to the root with a `DepKind` matching the `DepKind` of `id` and returns
+/// information about it.
 #[cold]
 #[inline(never)]
 pub(crate) fn find_dep_kind_root<'tcx>(
+    tcx: TyCtxt<'tcx>,
     id: QueryJobId,
     job_map: QueryJobMap<'tcx>,
-) -> (QueryJobInfo<'tcx>, usize) {
+) -> (Span, String, usize) {
     let mut depth = 1;
-    let info = &job_map.map[&id];
+    let mut info = &job_map.map[&id];
     let dep_kind = info.frame.dep_kind;
-    let mut current_id = info.job.parent;
-    let mut last_layout = (info.clone(), depth);
+    let mut last_info = info;
 
-    while let Some(id) = current_id {
-        let info = &job_map.map[&id];
+    while let Some(id) = info.job.parent {
+        info = &job_map.map[&id];
         if info.frame.dep_kind == dep_kind {
             depth += 1;
-            last_layout = (info.clone(), depth);
+            last_info = info;
         }
-        current_id = info.job.parent;
     }
-    last_layout
+    (last_info.job.span, last_info.frame.tagged_key.description(tcx), depth)
 }
 
 /// The locaton of a resumable waiter. The usize is the index into waiters in the query's latch.

compiler/rustc_query_impl/src/plumbing.rs

@@ -30,16 +30,16 @@
 
 fn depth_limit_error<'tcx>(tcx: TyCtxt<'tcx>, job: QueryJobId) {
     let job_map = collect_active_jobs_from_all_queries(tcx, CollectActiveJobsKind::Full);
-    let (info, depth) = find_dep_kind_root(job, job_map);
+    let (span, desc, depth) = find_dep_kind_root(tcx, job, job_map);
 
     let suggested_limit = match tcx.recursion_limit() {
         Limit(0) => Limit(2),
         limit => limit * 2,
     };
 
-    tcx.sess.dcx().emit_fatal(QueryOverflow {
-        span: info.job.span,
-        note: QueryOverflowNote { desc: info.frame.tagged_key.description(tcx), depth },
+    tcx.dcx().emit_fatal(QueryOverflow {
+        span,
+        note: QueryOverflowNote { desc, depth },
         suggested_limit,
         crate_name: tcx.crate_name(LOCAL_CRATE),
     });