2 files changed, 30 insertions, 20 deletions

diff --git a/tvix/cli/src/derivation.rs b/tvix/cli/src/derivation.rs
index 15c4c6f858f7..61c4489954f1 100644
--- a/tvix/cli/src/derivation.rs
+++ b/tvix/cli/src/derivation.rs
@@ -339,21 +339,27 @@ mod derivation_builtins {
         // eval data structures.
         drv.validate(false).map_err(Error::InvalidDerivation)?;
 
-        let tmp_replacement_str =
-            drv.calculate_drv_replacement_str(|drv| known_paths.get_replacement_string(drv));
+        // Calculate the derivation_or_fod_hash for the current derivation.
+        // This one is still intermediate (so not added to known_paths)
+        let derivation_or_fod_hash_tmp =
+            drv.derivation_or_fod_hash(|drv| known_paths.get_hash_derivation_modulo(drv));
 
-        drv.calculate_output_paths(&name, &tmp_replacement_str)
+        // Mutate the Derivation struct and set output paths
+        drv.calculate_output_paths(&name, &derivation_or_fod_hash_tmp)
             .map_err(Error::InvalidDerivation)?;
 
-        let actual_replacement_str =
-            drv.calculate_drv_replacement_str(|drv| known_paths.get_replacement_string(drv));
-
         let derivation_path = drv
             .calculate_derivation_path(&name)
             .map_err(Error::InvalidDerivation)?;
 
-        known_paths
-            .add_replacement_string(derivation_path.to_absolute_path(), &actual_replacement_str);
+        // recompute the hash derivation modulo and add to known_paths
+        let derivation_or_fod_hash_final =
+            drv.derivation_or_fod_hash(|drv| known_paths.get_hash_derivation_modulo(drv));
+
+        known_paths.add_hash_derivation_modulo(
+            derivation_path.to_absolute_path(),
+            &derivation_or_fod_hash_final,
+        );
 
         // mark all the new paths as known
         let output_names: Vec<String> = drv.outputs.keys().map(Clone::clone).collect();
diff --git a/tvix/cli/src/known_paths.rs b/tvix/cli/src/known_paths.rs
index f16fad902654..07373ef0da7a 100644
--- a/tvix/cli/src/known_paths.rs
+++ b/tvix/cli/src/known_paths.rs
@@ -12,6 +12,7 @@
 //! information.
 
 use crate::refscan::{ReferenceScanner, STORE_PATH_LEN};
+use nix_compat::nixhash::NixHash;
 use std::{
     collections::{hash_map, BTreeSet, HashMap},
     ops::Index,
@@ -67,11 +68,10 @@ pub struct KnownPaths {
     /// path used for reference scanning.
     paths: HashMap<PathName, KnownPath>,
 
-    /// All known replacement strings for derivations.
+    /// All known derivation or FOD hashes.
     ///
-    /// Keys are derivation paths, values are the opaque replacement
-    /// strings.
-    replacements: HashMap<String, String>,
+    /// Keys are derivation paths, values is the NixHash.
+    derivation_or_fod_hashes: HashMap<String, NixHash>,
 }
 
 impl Index<&PathName> for KnownPaths {
@@ -156,25 +156,29 @@ impl KnownPaths {
         ReferenceScanner::new(candidates)
     }
 
-    /// Fetch the opaque "replacement string" for a given derivation path.
-    pub fn get_replacement_string(&self, drv: &str) -> String {
+    /// Fetch the opaque "hash derivation modulo" for a given derivation path.
+    pub fn get_hash_derivation_modulo(&self, drv_path: &str) -> NixHash {
         // TODO: we rely on an invariant that things *should* have
         // been calculated if we get this far.
-        self.replacements[drv].clone()
+        self.derivation_or_fod_hashes[drv_path].clone()
     }
 
-    pub fn add_replacement_string<D: ToString>(&mut self, drv: D, replacement_str: &str) {
+    pub fn add_hash_derivation_modulo<D: ToString>(
+        &mut self,
+        drv: D,
+        hash_derivation_modulo: &NixHash,
+    ) {
         #[allow(unused_variables)] // assertions on this only compiled in debug builds
         let old = self
-            .replacements
-            .insert(drv.to_string(), replacement_str.to_owned());
+            .derivation_or_fod_hashes
+            .insert(drv.to_string(), hash_derivation_modulo.to_owned());
 
         #[cfg(debug_assertions)]
         {
             if let Some(old) = old {
                 debug_assert!(
-                    old == replacement_str,
-                    "replacement string for a given derivation should always match"
+                    old == *hash_derivation_modulo,
+                    "hash derivation modulo for a given derivation should always be calculated the same"
                 );
             }
         }