From fce0d37619736b0e56eabab8f9064fad471a2b5f Mon Sep 17 00:00:00 2001
From: Camille GILLOT <gillot.camille@gmail.com>
Date: Tue, 24 Mar 2020 23:50:47 +0100
Subject: [PATCH] Add comment.

---
 src/librustc_query_system/query/config.rs | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/librustc_query_system/query/config.rs b/src/librustc_query_system/query/config.rs
index 4800b66d889..10338f65471 100644
--- a/src/librustc_query_system/query/config.rs
+++ b/src/librustc_query_system/query/config.rs
@@ -20,6 +20,8 @@
 use std::fmt::Debug;
 use std::hash::Hash;
 
+// The parameter `CTX` is required in librustc: implementations may need to access the `'tcx`
+// lifetime in `CTX = TyCtxt<'tcx>`.
 pub trait QueryConfig<CTX> {
     const NAME: &'static str;
     const CATEGORY: ProfileCategory;
-- 
2.44.0