From b7066421339017d19101c7dc6cb11a8811a7909e Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Mon, 17 Feb 2025 11:50:54 +0100
Subject: [PATCH] resolveLookupPathPath(): Fix caching of negative lookups

This avoids spamming in case the missing search path entry does not
exist (#12480).

(cherry picked from commit df08e1e204d04924bc546ed3ebb2fabf936aa5be)
---
 src/libexpr/eval.cc | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index ee72436e4..463f361d3 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -3084,8 +3084,11 @@ std::optional<std::string> EvalState::resolveLookupPathPath(const LookupPath::Pa
     auto i = lookupPathResolved.find(value);
     if (i != lookupPathResolved.end()) return i->second;
 
-    auto finish = [&](std::string res) {
-        debug("resolved search path element '%s' to '%s'", value, res);
+    auto finish = [&](std::optional<std::string> res) {
+        if (res)
+            debug("resolved search path element '%s' to '%s'", value, *res);
+        else
+            debug("failed to resolve search path element '%s'", value);
         lookupPathResolved.emplace(value, res);
         return res;
     };
@@ -3137,9 +3140,7 @@ std::optional<std::string> EvalState::resolveLookupPathPath(const LookupPath::Pa
         }
     }
 
-    debug("failed to resolve search path element '%s'", value);
-    return std::nullopt;
-
+    return finish(std::nullopt);
 }