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refactor(nix-compat/derivation): emphasize aterm_bytes

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derivation_or_fod_hash constructs ATerm bytes and feeds them to sha256.

input_derivations being slightly modified is an implementation detail,
so move the BTreeMap construction inline, and have aterm_bytes in a
let binding (and feed it to the hash function directly while
constructing it).

This makes it a bit more understandable what's going on.

Change-Id: I2f5cfbd1c964fd39ac731ca39e76cfc168f4c7d7
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11147
Tested-by: BuildkiteCI
Autosubmit: flokli <flokli@flokli.de>
Reviewed-by: John Ericson <git@johnericson.me>
This commit is contained in:
Florian Klink 2024-03-14 14:32:52 +02:00 committed by clbot
parent 142c72e070
commit 905a79308e
1 changed files with 12 additions and 11 deletions
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23
tvix/nix-compat/src/derivation/mod.rs
View file

@ -97,7 +97,9 @@ impl Derivation {
self.to_aterm_bytes_with_replacements(&self.input_derivations)
}
/// Like `to_aterm_bytes` but allow input_derivation replacements for hashing.
/// Like `to_aterm_bytes`, but accept a different BTreeMap for input_derivations.
/// This is used to render the ATerm representation of a Derivation "modulo
/// fixed-output derivations".
fn to_aterm_bytes_with_replacements(
&self,
input_derivations: &BTreeMap<impl AtermWriteable, BTreeSet<String>>,
@ -203,19 +205,18 @@ impl Derivation {
// For each input_derivation, look up the
// derivation_or_fod_hash, and replace the derivation path with
// it's HEXLOWER digest.
let input_derivations = BTreeMap::from_iter(self.input_derivations.iter().map(
|(drv_path, output_names)| {
let hash = fn_get_derivation_or_fod_hash(&drv_path.into());
let aterm_bytes = self.to_aterm_bytes_with_replacements(&BTreeMap::from_iter(
self.input_derivations
.iter()
.map(|(drv_path, output_names)| {
let hash = fn_get_derivation_or_fod_hash(&drv_path.into());
(hash, output_names.to_owned())
},
(hash, output_names.to_owned())
}),
));
// write the ATerm of that to the hash function
let mut hasher = Sha256::new();
hasher.update(self.to_aterm_bytes_with_replacements(&input_derivations));
hasher.finalize().into()
// write the ATerm of that to the hash function and return its digest.
Sha256::new_with_prefix(aterm_bytes).finalize().into()
})
}