attempt to add Changes for compact serde serialization

CHANGELOG.md

@@ -3,6 +3,12 @@
 <!-- next-header -->
 ## Unreleased - ReleaseDate
 
+### Added
+
+- New `IntoChanges` trait and a parallel `*Changes` type per diff, projecting a diff to the subset of nodes that actually changed. Built-in implementations cover `Leaf`, the map/set diffs, and tuples.
+- The `Diffable` derive macro now recognizes `#[daft(changes)]` on structs as opt-in to generating a parallel `FooChanges` type and an `IntoChanges` impl. Opting in is required because the projection needs `Eq` (and, with the new `serde` feature, `Serialize`) on every leaf type — constraints existing users may not satisfy.
+- New `serde` feature emits `Serialize` impls for `Leaf` and every `*Changes` type, so a projected diff can be written to JSON (or any other serde format) with unchanged subtrees omitted entirely.
+
 ## [0.1.6] - 2026-05-14
 
 ### Added

Cargo.toml

@@ -30,6 +30,8 @@ paste = "1.0.15"
 prettyplease = "0.2.29"
 proc-macro2 = "1.0"
 quote = "1.0"
+serde = { version = "1.0.219", default-features = false }
+serde_json = "1.0.140"
 syn = "2.0"
 trybuild = "1.0.103"
 uuid = "1.12.0"

daft-derive/Cargo.toml

@@ -21,11 +21,19 @@ proc-macro2.workspace = true
 quote.workspace = true
 syn = { workspace = true, features = ["full", "visit"] }
 
+[features]
+# Mirror of daft's `serde` feature: emits the hand-written `Serialize` impl
+# on `*Changes` structs alongside the `IntoChanges` impl. Enabled
+# transitively when a downstream crate turns on `daft/serde`.
+serde = []
+
 [dev-dependencies]
-daft = { workspace = true, features = ["derive"] }
+daft = { workspace = true, features = ["derive", "serde"] }
 datatest-stable.workspace = true
 expectorate.workspace = true
 prettyplease.workspace = true
+serde = { workspace = true, features = ["derive"] }
+serde_json.workspace = true
 trybuild.workspace = true
 uuid = { workspace = true, features = ["v4"] }