Move depth_limit_error out of QueryContext trait.

It's defined and used in `rustc_query_impl`; `rustc_query_system`
doesn't need it. So it can just be an inherent method on `QueryCtxt`.

compiler/rustc_query_impl/src/plumbing.rs

@@ -48,6 +48,23 @@ impl<'tcx> QueryCtxt<'tcx> {
     pub fn new(tcx: TyCtxt<'tcx>) -> Self {
         QueryCtxt { tcx }
     }
+
+    fn depth_limit_error(self, job: QueryJobId) {
+        let query_map = self.collect_active_jobs(true).expect("failed to collect active queries");
+        let (info, depth) = job.find_dep_kind_root(query_map);
+
+        let suggested_limit = match self.tcx.recursion_limit() {
+            Limit(0) => Limit(2),
+            limit => limit * 2,
+        };
+
+        self.tcx.sess.dcx().emit_fatal(QueryOverflow {
+            span: info.job.span,
+            note: QueryOverflowNote { desc: info.frame.info.extract().description, depth },
+            suggested_limit,
+            crate_name: self.tcx.crate_name(LOCAL_CRATE),
+        });
+    }
 }
 
 impl<'tcx> HasDepContext for QueryCtxt<'tcx> {
@@ -155,23 +172,6 @@ impl<'tcx> QueryContext<'tcx> for QueryCtxt<'tcx> {
             tls::enter_context(&new_icx, compute)
         })
     }
-
-    fn depth_limit_error(self, job: QueryJobId) {
-        let query_map = self.collect_active_jobs(true).expect("failed to collect active queries");
-        let (info, depth) = job.find_dep_kind_root(query_map);
-
-        let suggested_limit = match self.tcx.recursion_limit() {
-            Limit(0) => Limit(2),
-            limit => limit * 2,
-        };
-
-        self.tcx.sess.dcx().emit_fatal(QueryOverflow {
-            span: info.job.span,
-            note: QueryOverflowNote { desc: info.frame.info.extract().description, depth },
-            suggested_limit,
-            crate_name: self.tcx.crate_name(LOCAL_CRATE),
-        });
-    }
 }
 
 pub(super) fn try_mark_green<'tcx>(tcx: TyCtxt<'tcx>, dep_node: &dep_graph::DepNode) -> bool {

compiler/rustc_query_system/src/query/mod.rs

@@ -181,6 +181,4 @@ pub trait QueryContext<'tcx>: HasDepContext {
     /// new query job while it executes.
     fn start_query<R>(self, token: QueryJobId, depth_limit: bool, compute: impl FnOnce() -> R)
     -> R;
-
-    fn depth_limit_error(self, job: QueryJobId);
 }