feat(tvix/nix-compat/derivation): make use of NixPath in some places

Some of these strings are actually just the nix hash representation of
the hash calculated earlier.

There's another one passed around via calculate_drv_replacement_str, but
that's left for a followup.

Change-Id: Id99a2a926a980d679eb49c34ee6a36bf224699b0
Reviewed-on: https://cl.tvl.fyi/c/depot/+/8218
Tested-by: BuildkiteCI
Reviewed-by: tazjin <tazjin@tvl.su>
Autosubmit: flokli <flokli@flokli.de>

tvix/nix-compat/src/derivation/mod.rs

@@ -1,4 +1,7 @@
-use crate::store_path::{self, StorePath};
+use crate::{
+    nixhash::NixHash,
+    store_path::{self, StorePath},
+};
 use serde::{Deserialize, Serialize};
 use sha2::{Digest, Sha256};
 use std::collections::{BTreeMap, BTreeSet};
@@ -100,7 +103,7 @@ impl Derivation {
     ///     This is: `text:`,
     ///     all d.InputDerivations and d.InputSources (sorted, separated by a `:`),
     ///     a `:`,
-    ///     a `sha256:`, followed by the sha256 digest of the ATerm representation (hex-encoded)
+    ///     the nix string representation of the sha256 sum of the ATerm representation
     ///     a `:`,
     ///     the storeDir, followed by a `:`,
     ///     the name of a derivation,
@@ -135,9 +138,11 @@ impl Derivation {
             derivation_hasher.finalize()
         };
 
+        let h = NixHash::new(crate::nixhash::HashAlgo::Sha256, aterm_digest.to_vec());
+
         s.push_str(&format!(
-            "sha256:{:x}:{}:{}.drv",
+            "{}:{}:{}.drv",
-            aterm_digest,
+            h.to_nix_hash_string(),
             store_path::STORE_DIR,
             name,
         ));

tvix/nix-compat/src/derivation/utils.rs

@@ -1,5 +1,6 @@
 use crate::derivation::DerivationError;
 use crate::nixbase32;
+use crate::nixhash::NixHash;
 use crate::store_path::{self, StorePath};
 use sha2::{Digest, Sha256};
 
@@ -67,9 +68,11 @@ pub fn path_with_references<S: AsRef<str>, I: IntoIterator<Item = S>, C: AsRef<[
         hasher.finalize()
     };
 
+    let h = NixHash::new(crate::nixhash::HashAlgo::Sha256, content_digest.to_vec());
+
     s.push_str(&format!(
-        ":sha256:{:x}:{}:{}",
+        ":{}:{}:{}",
-        content_digest,
+        h.to_nix_hash_string(),
         store_path::STORE_DIR,
         name
     ));