feat(tvix/nix-compat): generalize aterm writing for derivation r/7582

...so that we can also use `StorePath`s in
derivation.input_derivations.

Towards https://b.tvl.fyi/issues/264

Change-Id: I71d296ca273979c70f277a7f4f88a5f76de3d8be
Reviewed-on: https://cl.tvl.fyi/c/depot/+/10973
Reviewed-by: Peter Kolloch <info@eigenvalue.net>
Autosubmit: Peter Kolloch <info@eigenvalue.net>
Tested-by: BuildkiteCI
Reviewed-by: flokli <flokli@flokli.de>

1 files changed, 19 insertions, 6 deletions

diff --git a/tvix/nix-compat/src/derivation/mod.rs b/tvix/nix-compat/src/derivation/mod.rs
index 4d27bbb26d66..3a09c9d56632 100644
--- a/tvix/nix-compat/src/derivation/mod.rs
+++ b/tvix/nix-compat/src/derivation/mod.rs
@@ -22,6 +22,8 @@ pub use crate::nixhash::{CAHash, NixHash};
 pub use errors::{DerivationError, OutputError};
 pub use output::Output;
 
+use self::write::AtermWriteable;
+
 #[derive(Clone, Debug, Default, Eq, PartialEq, Serialize, Deserialize)]
 pub struct Derivation {
     #[serde(rename = "args")]
@@ -58,7 +60,7 @@ impl Derivation {
     fn serialize_with_replacements(
         &self,
         writer: &mut impl std::io::Write,
-        input_derivations: &BTreeMap<String, BTreeSet<String>>,
+        input_derivations: &BTreeMap<impl AtermWriteable, BTreeSet<String>>,
     ) -> Result<(), io::Error> {
         use write::*;
 
@@ -68,7 +70,19 @@ impl Derivation {
         write_outputs(writer, &self.outputs)?;
         write_char(writer, COMMA)?;
 
-        write_input_derivations(writer, input_derivations)?;
+        // To reproduce the exact hashes of original nix, we need to sort
+        // these by their aterm representation.
+        // StorePath has a different sort order, so we convert it here.
+        let input_derivations: BTreeMap<BString, &BTreeSet<String>> = input_derivations
+            .iter()
+            .map(|(k, v)| {
+                let mut aterm_k = Vec::new();
+                k.aterm_write(&mut aterm_k).expect("no write error to Vec");
+                (BString::new(aterm_k), v)
+            })
+            .collect();
+
+        write_input_derivations(writer, &input_derivations)?;
         write_char(writer, COMMA)?;
 
         write_input_sources(writer, &self.input_sources)?;
@@ -98,7 +112,7 @@ impl Derivation {
     /// Like `to_aterm_bytes` but allow input_derivation replacements for hashing.
     fn to_aterm_bytes_with_replacements(
         &self,
-        input_derivations: &BTreeMap<String, BTreeSet<String>>,
+        input_derivations: &BTreeMap<impl AtermWriteable, BTreeSet<String>>,
     ) -> Vec<u8> {
         let mut buffer: Vec<u8> = Vec::new();
 
@@ -202,10 +216,9 @@ impl Derivation {
                     let drv_path = StorePathRef::from_absolute_path(drv_path_str.as_bytes())
                         .expect("invalid input derivation path");
 
-                    let encoded_hash = data_encoding::HEXLOWER
-                        .encode(fn_get_derivation_or_fod_hash(&drv_path).digest_as_bytes());
+                    let hash = fn_get_derivation_or_fod_hash(&drv_path);
 
-                    (encoded_hash, output_names.to_owned())
+                    (hash, output_names.to_owned())
                 },
             ));