The last commit here fails to compile pushing it here to reference from an issue

Cargo.toml

@@ -4,7 +4,7 @@ members = ["buildpacks/ruby", "commons"]
 
 [workspace.package]
 edition = "2021"
-rust-version = "1.80"
+rust-version = "1.82"
 
 [workspace.lints.rust]
 unreachable_pub = "warn"

buildpacks/ruby/Cargo.toml

@@ -30,6 +30,7 @@ ureq = { version = "2", default-features = false, features = ["tls"] }
 url = "2"
 magic_migrate = "0.2"
 toml = "0.8"
+cache_diff = { version = "1.0.0", features = ["bullet_stream"] }
 
 [dev-dependencies]
 libcnb-test = "=0.26.1"

buildpacks/ruby/src/layers/bundle_download_layer.rs

@@ -9,6 +9,7 @@ use crate::RubyBuildpack;
 use crate::RubyBuildpackError;
 use bullet_stream::state::SubBullet;
 use bullet_stream::{style, Print};
+use cache_diff::CacheDiff;
 use commons::gemfile_lock::ResolvedBundlerVersion;
 use fun_run::{self, CommandWithName};
 use libcnb::data::layer_name;
@@ -59,20 +60,13 @@ try_migrate_deserializer_chain!(
 
 impl MetadataDiff for Metadata {
     fn diff(&self, other: &Self) -> Vec<String> {
-        let mut differences = Vec::new();
-        if self.version != other.version {
-            differences.push(format!(
-                "Bundler version ({old} to {now})",
-                old = style::value(other.version.to_string()),
-                now = style::value(self.version.to_string())
-            ));
-        }
-        differences
+        <Self as CacheDiff>::diff(self, other)
     }
 }
 
-#[derive(Deserialize, Serialize, Debug, Clone)]
+#[derive(Deserialize, Serialize, Debug, Clone, CacheDiff)]
 pub(crate) struct MetadataV1 {
+    #[cache_diff(rename = "Bundler version")]
     pub(crate) version: ResolvedBundlerVersion,
 }
 
@@ -141,12 +135,14 @@ mod test {
         let old = Metadata {
             version: ResolvedBundlerVersion("2.3.5".to_string()),
         };
-        assert!(old.diff(&old).is_empty());
+        assert!(CacheDiff::diff(&old, &old).is_empty());
 
-        let diff = Metadata {
-            version: ResolvedBundlerVersion("2.3.6".to_string()),
-        }
-        .diff(&old);
+        let diff = CacheDiff::diff(
+            &Metadata {
+                version: ResolvedBundlerVersion("2.3.6".to_string()),
+            },
+            &old,
+        );
         assert_eq!(
             diff.iter().map(strip_ansi).collect::<Vec<String>>(),
             vec!["Bundler version (`2.3.5` to `2.3.6`)"]

buildpacks/ruby/src/layers/bundle_install_layer.rs

@@ -118,7 +118,7 @@ pub(crate) fn handle(
 
 pub(crate) type Metadata = MetadataV2;
 try_migrate_deserializer_chain!(
-    chain: [MetadataV1, MetadataV2],
+    chain: [MetadataV1, MetadataV2, MetadataV3],
     error: MetadataMigrateError,
     deserializer: toml::Deserializer::new,
 );
@@ -176,6 +176,15 @@ pub(crate) struct MetadataV2 {
     pub(crate) cpu_architecture: String,
     pub(crate) ruby_version: ResolvedRubyVersion,
     pub(crate) force_bundle_install_key: String,
+    pub(crate) digest: MetadataDigest, // Must be last for serde to be happy https://github.com/toml-rs/toml-rs/issues/142
+}
+
+#[derive(Deserialize, Serialize, Debug, Clone, Eq, PartialEq)]
+pub(crate) struct MetadataV3 {
+    pub(crate) os_distribution: String,
+    pub(crate) cpu_architecture: String,
+    pub(crate) ruby_version: ResolvedRubyVersion,
+    pub(crate) force_bundle_install_key: String,
 
     /// A struct that holds the cryptographic hash of components that can
     /// affect the result of `bundle install`. When these values do not
@@ -217,6 +226,20 @@ impl TryFrom<MetadataV1> for MetadataV2 {
     }
 }
 
+impl TryFrom<MetadataV2> for MetadataV3 {
+    type Error = Infallible;
+
+    fn try_from(v2: MetadataV2) -> Result<Self, Self::Error> {
+        Ok(Self {
+            os_distribution: format!("{} {}", v2.distro_name, v2.distro_version),
+            cpu_architecture: v2.cpu_architecture,
+            ruby_version: v2.ruby_version,
+            force_bundle_install_key: v2.force_bundle_install_key,
+            digest: v2.digest,
+        })
+    }
+}
+
 #[derive(Debug)]
 enum InstallState {
     /// Holds message indicating the reason why we want to run 'bundle install'