From 444af855523b00b0959273bab9d7343312817cb3 Mon Sep 17 00:00:00 2001
From: Yorick van Pelt <yorick@yorickvanpelt.nl>
Date: Wed, 5 Oct 2022 12:09:57 +0200
Subject: Temporarily disable the debugger during completion evaluation

readline is not re-entrant, so entering the debugger from the
completioncallback results in an eventual segfault.

The workaround is to temporarily disable the debugger when searching
for possible completions.
---
 src/libcmd/repl.cc | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/libcmd/repl.cc b/src/libcmd/repl.cc
index df8932087..bb254ff8d 100644
--- a/src/libcmd/repl.cc
+++ b/src/libcmd/repl.cc
@@ -384,6 +384,10 @@ StringSet NixRepl::completePrefix(const std::string & prefix)
             i++;
         }
     } else {
+        /* Temporarily disable the debugger, to avoid re-entering readline. */
+        auto debug_repl = state->debugRepl;
+        state->debugRepl = nullptr;
+        Finally restoreDebug([&]() { state->debugRepl = debug_repl; });
         try {
             /* This is an expression that should evaluate to an
                attribute set.  Evaluate it to get the names of the
-- 
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