From 9ac91e36a96533bcf2259ab31e995c07d640ca15 Mon Sep 17 00:00:00 2001
From: Amaan Qureshi <git@amaanq.com>
Date: Thu, 12 Feb 2026 19:37:24 -0500
Subject: [PATCH] libstore: make substitution use the per-store `getReadOnly`
 method

This commit introduces a `getReadOnly` method on the store config that returns if the current store is read only or not. This is then used in subtitution, so we fail gracefully with a nice error message if only the individual store is read-only.

As a bonus, it gets us one step closer to getting rid of the global because we can use the per-store method instead.

Progress on #5638
---
 src/libstore/build/substitution-goal.cc       | 2 +-
 src/libstore/dummy-store.cc                   | 5 +++++
 src/libstore/include/nix/store/dummy-store.hh | 2 ++
 src/libstore/include/nix/store/local-store.hh | 2 ++
 src/libstore/include/nix/store/store-api.hh   | 6 ++++++
 src/libstore/local-store.cc                   | 5 +++++
 src/libstore/store-api.cc                     | 5 +++++
 7 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/src/libstore/build/substitution-goal.cc b/src/libstore/build/substitution-goal.cc
index 541487bbc..d58bec885 100644
--- a/src/libstore/build/substitution-goal.cc
+++ b/src/libstore/build/substitution-goal.cc
@@ -37,7 +37,7 @@ Goal::Co PathSubstitutionGoal::init()
         co_return doneSuccess(BuildResult::Success{.status = BuildResult::Success::AlreadyValid});
     }
 
-    if (settings.readOnlyMode)
+    if (worker.store.config.getReadOnly())
         throw Error(
             "cannot substitute path '%s' - no write access to the Nix store", worker.store.printStorePath(storePath));
 
diff --git a/src/libstore/dummy-store.cc b/src/libstore/dummy-store.cc
index ba42c773b..d45133e5a 100644
--- a/src/libstore/dummy-store.cc
+++ b/src/libstore/dummy-store.cc
@@ -119,6 +119,11 @@ ref<Store> DummyStoreConfig::openStore() const
     return openDummyStore();
 }
 
+bool DummyStoreConfig::getReadOnly() const
+{
+    return readOnly.get() || StoreConfig::getReadOnly();
+}
+
 struct DummyStoreImpl : DummyStore
 {
     using Config = DummyStoreConfig;
diff --git a/src/libstore/include/nix/store/dummy-store.hh b/src/libstore/include/nix/store/dummy-store.hh
index febf351c9..59d1b1fdd 100644
--- a/src/libstore/include/nix/store/dummy-store.hh
+++ b/src/libstore/include/nix/store/dummy-store.hh
@@ -35,6 +35,8 @@ struct DummyStoreConfig : public std::enable_shared_from_this<DummyStoreConfig>,
           No additional memory will be used, because no information needs to be stored.
         )"};
 
+    bool getReadOnly() const override;
+
     static const std::string name()
     {
         return "Dummy Store";
diff --git a/src/libstore/include/nix/store/local-store.hh b/src/libstore/include/nix/store/local-store.hh
index f381f5088..7b6b45324 100644
--- a/src/libstore/include/nix/store/local-store.hh
+++ b/src/libstore/include/nix/store/local-store.hh
@@ -117,6 +117,8 @@ public:
           > While the filesystem the database resides on might appear to be read-only, consider whether another user or system might have write access to it.
         )"};
 
+    bool getReadOnly() const override;
+
     Setting<bool> ignoreGcDeleteFailure{
         this,
         false,
diff --git a/src/libstore/include/nix/store/store-api.hh b/src/libstore/include/nix/store/store-api.hh
index 2fb8a4260..9961652e0 100644
--- a/src/libstore/include/nix/store/store-api.hh
+++ b/src/libstore/include/nix/store/store-api.hh
@@ -218,6 +218,12 @@ struct StoreConfig : public StoreConfigBase, public StoreDirConfig
         // Don't document the machine-specific default value
         false};
 
+    /**
+     * Whether we're allowed to write to this store, also takes into account
+     * global `readOnly`'s mode setting, not just any per-store settings.
+     */
+    virtual bool getReadOnly() const;
+
     /**
      * Open a store of the type corresponding to this configuration
      * type.
diff --git a/src/libstore/local-store.cc b/src/libstore/local-store.cc
index 8560284a3..addb8a9f2 100644
--- a/src/libstore/local-store.cc
+++ b/src/libstore/local-store.cc
@@ -473,6 +473,11 @@ StoreReference LocalStoreConfig::getReference() const
     };
 }
 
+bool LocalStoreConfig::getReadOnly() const
+{
+    return readOnly.get() || StoreConfig::getReadOnly();
+}
+
 int LocalStore::getSchema()
 {
     int curSchema = 0;
diff --git a/src/libstore/store-api.cc b/src/libstore/store-api.cc
index bc7df176b..e46a5ca43 100644
--- a/src/libstore/store-api.cc
+++ b/src/libstore/store-api.cc
@@ -333,6 +333,11 @@ StoreReference StoreConfig::getReference() const
     return {.variant = StoreReference::Auto{}};
 }
 
+bool StoreConfig::getReadOnly() const
+{
+    return settings.readOnlyMode;
+}
+
 bool Store::PathInfoCacheValue::isKnownNow()
 {
     std::chrono::duration ttl = didExist() ? std::chrono::seconds(settings.ttlPositiveNarInfoCache)