From 3cfac9b0794cdd2ee80fc540f83feca15596c35c Mon Sep 17 00:00:00 2001
From: John Ericson <John.Ericson@Obsidian.Systems>
Date: Mon, 15 Dec 2025 00:53:45 -0500
Subject: [PATCH] Allow `Worker` instances to be locally configured with
 substituters

This will be useful for unit tests.
---
 src/libstore/build/drv-output-substitution-goal.cc | 4 +---
 src/libstore/build/substitution-goal.cc            | 3 +--
 src/libstore/build/worker.cc                       | 2 ++
 src/libstore/include/nix/store/build/worker.hh     | 9 +++++++++
 4 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/src/libstore/build/drv-output-substitution-goal.cc b/src/libstore/build/drv-output-substitution-goal.cc
index 8d0a307be..5b3a407d9 100644
--- a/src/libstore/build/drv-output-substitution-goal.cc
+++ b/src/libstore/build/drv-output-substitution-goal.cc
@@ -3,8 +3,6 @@
 #include "nix/store/build/worker.hh"
 #include "nix/store/build/substitution-goal.hh"
 #include "nix/util/callback.hh"
-#include "nix/store/store-open.hh"
-#include "nix/store/globals.hh"
 
 namespace nix {
 
@@ -25,7 +23,7 @@ Goal::Co DrvOutputSubstitutionGoal::init()
         co_return amDone(ecSuccess);
     }
 
-    auto subs = settings.useSubstitutes ? getDefaultSubstituters() : std::list<ref<Store>>();
+    auto subs = worker.getSubstituters();
 
     bool substituterFailed = false;
 
diff --git a/src/libstore/build/substitution-goal.cc b/src/libstore/build/substitution-goal.cc
index ac18de304..f066f013d 100644
--- a/src/libstore/build/substitution-goal.cc
+++ b/src/libstore/build/substitution-goal.cc
@@ -1,5 +1,4 @@
 #include "nix/store/build/worker.hh"
-#include "nix/store/store-open.hh"
 #include "nix/store/build/substitution-goal.hh"
 #include "nix/store/nar-info.hh"
 #include "nix/util/finally.hh"
@@ -60,7 +59,7 @@ Goal::Co PathSubstitutionGoal::init()
         throw Error(
             "cannot substitute path '%s' - no write access to the Nix store", worker.store.printStorePath(storePath));
 
-    auto subs = settings.useSubstitutes ? getDefaultSubstituters() : std::list<ref<Store>>();
+    auto subs = worker.getSubstituters();
 
     bool substituterFailed = false;
     std::optional<Error> lastStoresException = std::nullopt;
diff --git a/src/libstore/build/worker.cc b/src/libstore/build/worker.cc
index 3663a2c91..c066fe206 100644
--- a/src/libstore/build/worker.cc
+++ b/src/libstore/build/worker.cc
@@ -1,5 +1,6 @@
 #include "nix/store/local-store.hh"
 #include "nix/store/machines.hh"
+#include "nix/store/store-open.hh"
 #include "nix/store/build/worker.hh"
 #include "nix/store/build/substitution-goal.hh"
 #include "nix/store/build/drv-output-substitution-goal.hh"
@@ -21,6 +22,7 @@ Worker::Worker(Store & store, Store & evalStore)
     , actSubstitutions(*logger, actCopyPaths)
     , store(store)
     , evalStore(evalStore)
+    , getSubstituters{[] { return settings.useSubstitutes ? getDefaultSubstituters() : std::list<ref<Store>>{}; }}
 {
     nrLocalBuilds = 0;
     nrSubstitutions = 0;
diff --git a/src/libstore/include/nix/store/build/worker.hh b/src/libstore/include/nix/store/build/worker.hh
index 173f7b222..65408429c 100644
--- a/src/libstore/include/nix/store/build/worker.hh
+++ b/src/libstore/include/nix/store/build/worker.hh
@@ -8,6 +8,7 @@
 #include "nix/store/realisation.hh"
 #include "nix/util/muxable-pipe.hh"
 
+#include <functional>
 #include <future>
 #include <thread>
 
@@ -171,6 +172,14 @@ public:
     Store & store;
     Store & evalStore;
 
+    /**
+     * Function to get the substituters to use for path substitution.
+     *
+     * Defaults to `getDefaultSubstituters`. This allows tests to
+     * inject custom substituters.
+     */
+    std::function<std::list<ref<Store>>()> getSubstituters;
+
 #ifndef _WIN32 // TODO Enable building on Windows
     std::unique_ptr<HookInstance> hook;
 #endif