[16/n] add a derive feature

The derive macro isn't necessary for functionality, so some users might want to
turn it off. Add it as a feature.

Also group together third-party implementations so we only test 18 combinations
rather than 65.

Reviewers: andrewjstone

Reviewed By: andrewjstone

Pull Request: #47

Author: sunshowers

Justfile

@@ -6,7 +6,9 @@ help:
 
 # Run `cargo hack --feature-powerset` on crates
 powerset *args:
-    cargo hack --feature-powerset --workspace {{args}}
+    # Group third-party implementation features to avoid a full combinatorial
+    # explosion -- we assume that they build independent of each other.
+    cargo hack --feature-powerset --workspace {{args}} --group-features newtype-uuid1,oxnet01,uuid1 --ignore-unknown-features
 
 # Build docs for crates and direct dependencies
 rustdoc *args:

daft-derive/Cargo.toml

@@ -20,7 +20,7 @@ quote.workspace = true
 syn = { workspace = true, features = ["full", "visit"] }
 
 [dev-dependencies]
-daft.workspace = true
+daft = { workspace = true, features = ["derive"] }
 datatest-stable.workspace = true
 expectorate.workspace = true
 prettyplease.workspace = true

daft/Cargo.toml

@@ -12,7 +12,7 @@ license.workspace = true
 workspace = true
 
 [dependencies]
-daft-derive.workspace = true
+daft-derive = { workspace = true, optional = true }
 newtype-uuid = { workspace = true, optional = true }
 oxnet = { workspace = true, optional = true }
 paste.workspace = true
@@ -22,6 +22,7 @@ uuid = { workspace = true, optional = true, features = ["v4"] }
 default = ["std"]
 std = ["alloc"]
 alloc = []
+derive = ["dep:daft-derive"]
 newtype-uuid1 = ["dep:newtype-uuid"]
 oxnet01 = ["dep:oxnet"]
 uuid1 = ["dep:uuid"]

daft/README.md

@@ -356,7 +356,8 @@ diff types directly.
 
 #### Example
 
-Some structs like identifiers should be treated as leaf nodes:
+Some structs like identifiers should be treated as leaf nodes. This can be
+implemented via `#[daft(leaf)]`, but also manually:
 
 ````rust
 use daft::{Diffable, Leaf};
@@ -409,6 +410,8 @@ struct BorrowedDataDiff<'daft, 'a: 'daft, 'b: 'daft, T: ?Sized + 'daft> {
 
 ## Optional features
 
+* `derive`: Enable the `Diffable` derive macro: **disabled** by default.
+
 Implementations for standard library types, all **enabled** by default:
 
 * `alloc`: Enable diffing for types from the [`alloc`](https://doc.rust-lang.org/nightly/alloc/index.html) crate.

daft/src/lib.rs

@@ -18,7 +18,7 @@
 //! # Usage
 //!
 //! ```rust
-//! # #[cfg(feature = "std")] {
+//! # #[cfg(all(feature = "std", feature = "derive"))] {
 //! use daft::{Diffable, Leaf};
 //!
 //! // Annotate your struct with `#[derive(Diffable)]`:
@@ -94,6 +94,7 @@
 //! assert_eq!(diff.before, Some(&1));
 //! assert_eq!(diff.after, Some(&2));
 //!
+//! # #[cfg(feature = "derive")] {
 //! // Automatically derived enums also use Leaf:
 //! #[derive(Debug, PartialEq, Eq, Diffable)]
 //! enum MyEnum {
@@ -107,6 +108,7 @@
 //! let diff: Leaf<&MyEnum> = before.diff(&after);
 //! assert_eq!(diff.before, &before);
 //! assert_eq!(diff.after, &after);
+//! # }
 //! ```
 //!
 //! Vectors use `Leaf` as well:
@@ -267,7 +269,7 @@
 //! Tuple-like structs produce tuple-like diff structs:
 //!
 //! ```rust
-//! # #[cfg(feature = "std")] {
+//! # #[cfg(all(feature = "std", feature = "derive"))] {
 //! use daft::Diffable;
 //! use std::collections::BTreeMap;
 //!
@@ -288,6 +290,7 @@
 //! An example with `#[daft(leaf)]` on **structs**:
 //!
 //! ```rust
+//! # #[cfg(feature = "derive")] {
 //! use daft::{Diffable, Leaf};
 //!
 //! #[derive(Diffable)]
@@ -302,11 +305,13 @@
 //!
 //! assert_eq!(diff.before.a, 1);
 //! assert_eq!(diff.after.a, 2);
+//! # }
 //! ```
 //!
 //! An example with `#[daft(leaf)]` on **struct fields**:
 //!
 //! ```rust
+//! # #[cfg(feature = "derive")] {
 //! use daft::{Diffable, Leaf};
 //!
 //! // A simple struct that implements Diffable.
@@ -353,6 +358,7 @@
 //!
 //! // `PlainStruct` can also be compared even though it doesn't implement `Diffable`.
 //! assert_eq!(diff.plain, Leaf { before: &PlainStruct(1), after: &PlainStruct(2) });
+//! # }
 //! ```
 //!
 //! ### Custom diff types
@@ -364,7 +370,8 @@
 //!
 //! ### Example
 //!
-//! Some structs like identifiers should be treated as leaf nodes:
+//! Some structs like identifiers should be treated as leaf nodes. This can be
+//! implemented via `#[daft(leaf)]`, but also manually:
 //!
 //! ```rust
 //! # #[cfg(feature = "std")] {
@@ -400,6 +407,7 @@
 //! ### Example
 //!
 //! ```rust
+//! # #[cfg(feature = "derive")] {
 //! use daft::Diffable;
 //!
 //! #[derive(Diffable)]
@@ -417,10 +425,13 @@
 //!     b: T::Diff<'daft>,
 //! }
 //! # */
+//! # }
 //! ```
 //!
 //! # Optional features
 //!
+//! * `derive`: Enable the `Diffable` derive macro: **disabled** by default.
+//!
 //! Implementations for standard library types, all **enabled** by default:
 //!
 //! * `alloc`: Enable diffing for types from the [`alloc`] crate.
@@ -507,6 +518,7 @@ pub use alloc_impls::*;
 ///   diff.
 ///
 /// For more information, see the [crate-level documentation](crate).
+#[cfg(feature = "derive")]
 pub use daft_derive::Diffable;
 pub use diffable::*;
 pub use leaf::*;