feat: Only save md5 in lock file if no sha256 is present (#764)

By saving only one of those two hashes, we reduce the lock file size a
bit. This should be especially noticeable in git repos, since hashes
compress poorly.

This PR is a contribution to improving
prefix-dev/pixi#1509

crates/rattler_lock/src/hash.rs

@@ -7,18 +7,15 @@ use serde_with::skip_serializing_none;
 /// This implementation of the `Deserialize` trait for the `PackageHashes` struct
 ///
 /// It expects the input to have either a `md5` field, a `sha256` field, or both.
-/// If both fields are present, it constructs a `Md5Sha256` instance with their values.
+/// If the `sha256` field is present, it constructs a `Sha256` instance with its value.
 /// If only the `md5` field is present, it constructs a `Md5` instance with its value.
-/// If only the `sha256` field is present, it constructs a `Sha256` instance with its value.
 /// If neither field is present it returns an error
 #[derive(Eq, PartialEq, Hash, Clone, Debug)]
 pub enum PackageHashes {
     /// Contains an MD5 hash
     Md5(Md5Hash),
     /// Contains as Sha256 Hash
     Sha256(Sha256Hash),
-    /// Contains both hashes
-    Md5Sha256(Md5Hash, Sha256Hash),
 }
 
 impl PartialOrd for PackageHashes {
@@ -36,11 +33,10 @@ impl Ord for PackageHashes {
 impl PackageHashes {
     /// Create correct enum from hashes
     pub fn from_hashes(md5: Option<Md5Hash>, sha256: Option<Sha256Hash>) -> Option<PackageHashes> {
-        use PackageHashes::{Md5, Md5Sha256, Sha256};
+        use PackageHashes::{Md5, Sha256};
         match (md5, sha256) {
+            (_, Some(sha256)) => Some(Sha256(sha256)),
             (Some(md5), None) => Some(Md5(md5)),
-            (None, Some(sha256)) => Some(Sha256(sha256)),
-            (Some(md5), Some(sha256)) => Some(Md5Sha256(md5, sha256)),
             (None, None) => None,
         }
     }
@@ -49,15 +45,15 @@ impl PackageHashes {
     pub fn sha256(&self) -> Option<&Sha256Hash> {
         match self {
             PackageHashes::Md5(_) => None,
-            PackageHashes::Sha256(sha256) | PackageHashes::Md5Sha256(_, sha256) => Some(sha256),
+            PackageHashes::Sha256(sha256) => Some(sha256),
         }
     }
 
     /// Returns the MD5 hash
     pub fn md5(&self) -> Option<&Md5Hash> {
         match self {
             PackageHashes::Sha256(_) => None,
-            PackageHashes::Md5(md5) | PackageHashes::Md5Sha256(md5, _) => Some(md5),
+            PackageHashes::Md5(md5) => Some(md5),
         }
     }
 
@@ -66,7 +62,6 @@ impl PackageHashes {
         match self {
             PackageHashes::Sha256(sha256) => sha256.to_vec(),
             PackageHashes::Md5(md5) => md5.to_vec(),
-            PackageHashes::Md5Sha256(md5, sha256) => [md5.to_vec(), sha256.to_vec()].concat(),
         }
     }
 }
@@ -83,7 +78,7 @@ impl Serialize for PackageHashes {
     where
         S: Serializer,
     {
-        use PackageHashes::{Md5, Md5Sha256, Sha256};
+        use PackageHashes::{Md5, Sha256};
         let raw = match self {
             Md5(hash) => RawPackageHashes {
                 md5: Some(SerializableHash::from(*hash)),
@@ -93,10 +88,6 @@ impl Serialize for PackageHashes {
                 md5: None,
                 sha256: Some(SerializableHash::from(*hash)),
             },
-            Md5Sha256(md5hash, sha) => RawPackageHashes {
-                md5: Some(SerializableHash::from(*md5hash)),
-                sha256: Some(SerializableHash::from(*sha)),
-            },
         };
         raw.serialize(serializer)
     }
@@ -105,24 +96,22 @@ impl Serialize for PackageHashes {
 // This implementation of the `Deserialize` trait for the `PackageHashes` struct
 //
 // It expects the input to have either a `md5` field, a `sha256` field, or both.
-// If both fields are present, it constructs a `Md5Sha256` instance with their values.
+// If the `sha256` field is present, it constructs a `Sha256` instance with its value.
 // If only the `md5` field is present, it constructs a `Md5` instance with its value.
-// If only the `sha256` field is present, it constructs a `Sha256` instance with its value.
 // If neither field is present it returns an error
 impl<'de> Deserialize<'de> for PackageHashes {
     fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
     where
         D: Deserializer<'de>,
     {
-        use PackageHashes::{Md5, Md5Sha256, Sha256};
+        use PackageHashes::{Md5, Sha256};
         let temp = RawPackageHashes::deserialize(deserializer)?;
         Ok(match (temp.md5, temp.sha256) {
-            (Some(md5), Some(sha)) => Md5Sha256(md5.into(), sha.into()),
+            (_, Some(sha)) => Sha256(sha.into()),
             (Some(md5), None) => Md5(md5.into()),
-            (None, Some(sha)) => Sha256(sha.into()),
             _ => {
                 return Err(D::Error::custom(
-                    "Expected `sha256` field `md5` field or both",
+                    "Expected `sha256` field, `md5` field or both",
                 ))
             }
         })
@@ -140,9 +129,8 @@ mod test {
           md5: 4eccaeba205f0aed9ac3a9ea58568ca3
           sha256: f240217476e148e825420c6bc3a0c0efb08c0718b7042fae960400c02af858a3
     "#;
-
         let result: PackageHashes = from_str(yaml).unwrap();
-        assert!(matches!(result, PackageHashes::Md5Sha256(_, _)));
+        assert!(matches!(result, PackageHashes::Sha256(_)));
 
         let yaml = r#"
           md5: 4eccaeba205f0aed9ac3a9ea58568ca3

crates/rattler_lock/src/parse/v3.rs

@@ -138,13 +138,11 @@ pub fn parse_v3_or_lower(
         let pkg: EnvironmentPackageData = match kind {
             LockedPackageKindV3::Conda(value) => {
                 let md5 = match value.hash {
-                    PackageHashes::Md5(md5) | PackageHashes::Md5Sha256(md5, _) => Some(md5),
+                    PackageHashes::Md5(md5) => Some(md5),
                     PackageHashes::Sha256(_) => None,
                 };
                 let sha256 = match value.hash {
-                    PackageHashes::Sha256(sha256) | PackageHashes::Md5Sha256(_, sha256) => {
-                        Some(sha256)
-                    }
+                    PackageHashes::Sha256(sha256) => Some(sha256),
                     PackageHashes::Md5(_) => None,
                 };