From 4a920b46da219ca7de4c9fe00038e82dab1b22f4 Mon Sep 17 00:00:00 2001
From: Valentin Gagarin <valentin.gagarin@tweag.io>
Date: Wed, 4 Sep 2024 21:26:18 +0200
Subject: [PATCH] only set default values for `nix-path` if nothing else is set

TODO: this doesn't work yet.
we currently have no way of checking if a config value was set or not.

this is the expected behavior for default values:
new values should override them, not prepend.

the change fixes a logic bug introduced when fixing the previously confused
override mechanism in e0620213146b1a581533302a2fab54af21d49685.
---
 src/libexpr/eval-gc.cc       | 2 +-
 src/libexpr/eval.cc          | 1 +
 tests/functional/nix_path.sh | 6 ++++++
 3 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/src/libexpr/eval-gc.cc b/src/libexpr/eval-gc.cc
index 07ce05a2c..de0b53865 100644
--- a/src/libexpr/eval-gc.cc
+++ b/src/libexpr/eval-gc.cc
@@ -101,7 +101,7 @@ void initGC()
 #endif
 
     // NIX_PATH must override the regular setting
-    // See the comment in applyConfig
+    // See the XXX comment in `applyConfig()`
     if (auto nixPathEnv = getEnv("NIX_PATH")) {
         globalConfig.set("nix-path", concatStringsSep(" ", EvalSettings::parseNixPath(nixPathEnv.value())));
     }
diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 2420f15c1..345acb6d2 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -341,6 +341,7 @@ EvalState::EvalState(
         for (auto & i : settings.nixPath.get()) {
             lookupPath.elements.emplace_back(LookupPath::Elem::parse(i));
         }
+        // TODO: only set if nothing else is
         if (!settings.restrictEval) {
             for (auto & i : EvalSettings::getDefaultNixPath()) {
                 lookupPath.elements.emplace_back(LookupPath::Elem::parse(i));
diff --git a/tests/functional/nix_path.sh b/tests/functional/nix_path.sh
index 90cba1f0c..5557ab7d5 100755
--- a/tests/functional/nix_path.sh
+++ b/tests/functional/nix_path.sh
@@ -42,6 +42,12 @@ done
 # finding something that's not in any of the default paths fails
 ( ! $(nix-instantiate --find-file test) )
 
+# setting anything overrides the default paths
+# this ensures we can force an empty search path
+[[ $(NIX_PATH= nix-instantiate --eval -E 'with builtins; length nixPath') = 0 ]]
+[[ $(nix-instantiate --nix-path "" --eval -E 'with builtins; length nixPath') = 0 ]]
+[[ $(nix-instantiate -I "" --eval -E 'with builtins; length nixPath') = 1 ]]
+
 echo "nix-path = test=$TEST_ROOT/from-nix-path-file" >> "$test_nix_conf"
 
 # Use nix.conf in absence of NIX_PATH