From e1a72c29aaef3b3145296dfc9e24201b3c655768 Mon Sep 17 00:00:00 2001
From: Camille GILLOT <gillot.camille@gmail.com>
Date: Tue, 1 Feb 2022 18:46:04 +0100
Subject: [PATCH] Explain &Arc.

---
 compiler/rustc_middle/src/query/mod.rs | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/compiler/rustc_middle/src/query/mod.rs b/compiler/rustc_middle/src/query/mod.rs
index 1861f547fca1..fc2750d23039 100644
--- a/compiler/rustc_middle/src/query/mod.rs
+++ b/compiler/rustc_middle/src/query/mod.rs
@@ -1681,6 +1681,10 @@ rustc_queries! {
         desc { "optimization level used by backend" }
     }
 
+    /// Return the filenames where output artefacts shall be stored.
+    ///
+    /// This query returns an `&Arc` because codegen backends need the value even after the `TyCtxt`
+    /// has been destroyed.
     query output_filenames(_: ()) -> &'tcx Arc<OutputFilenames> {
         eval_always
         desc { "output_filenames" }