1 files changed, 16 insertions, 0 deletions
diff --git a/src/libexpr/eval-cache.cc b/src/libexpr/eval-cache.cc
index a47a539f5..3a18b71d4 100644
--- a/src/libexpr/eval-cache.cc
+++ b/src/libexpr/eval-cache.cc
@@ -2,6 +2,7 @@
 #include "sqlite.hh"
 #include "eval.hh"
 #include "eval-inline.hh"
+#include "store-api.hh"
 
 namespace nix::eval_cache {
 
@@ -502,4 +503,19 @@ bool AttrCursor::isDerivation()
     return aType && aType->getString() == "derivation";
 }
 
+StorePath AttrCursor::forceDerivation()
+{
+    auto aDrvPath = getAttr(root->state.sDrvPath);
+    auto drvPath = root->state.store->parseStorePath(aDrvPath->getString());
+    if (!root->state.store->isValidPath(drvPath) && !settings.readOnlyMode) {
+        /* The eval cache contains 'drvPath', but the actual path has
+           been garbage-collected. So force it to be regenerated. */
+        aDrvPath->forceValue();
+        if (!root->state.store->isValidPath(drvPath))
+            throw Error("don't know how to recreate store derivation '%s'!",
+                root->state.store->printStorePath(drvPath));
+    }
+    return drvPath;
+}
+
 }