From 97906bcd5c9c5ba5d165c7330b2ee062a97f11cf Mon Sep 17 00:00:00 2001
From: Aaron Hill <aa1ronham@gmail.com>
Date: Thu, 26 Sep 2019 16:55:07 -0400
Subject: [PATCH] Add note about global state in try_print_query_stack

---
 src/librustc/ty/query/plumbing.rs | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/librustc/ty/query/plumbing.rs b/src/librustc/ty/query/plumbing.rs
index e2dff46d18b16..d3e6789b826a9 100644
--- a/src/librustc/ty/query/plumbing.rs
+++ b/src/librustc/ty/query/plumbing.rs
@@ -325,6 +325,9 @@ impl<'tcx> TyCtxt<'tcx> {
     pub fn try_print_query_stack(handler: &Handler) {
         eprintln!("query stack during panic:");
 
+        // Be careful reyling on global state here: this code is called from
+        // a panic hook, which means that the global `Handler` may be in a weird
+        // state if it was responsible for triggering the panic.
         tls::with_context_opt(|icx| {
             if let Some(icx) = icx {
                 let mut current_query = icx.query.clone();