feat: Add a feature to disable map support

The `map` feature, enabled by default, can be disable to remove
map support, for codebases not supporting diffs over map to be
expressed.

See redbadger/pathogen#1 for some context
on when map support might not be present.

Author: DeltaEvo

Cargo.toml

@@ -28,6 +28,11 @@ thiserror = "1.0"
 uuid = { version = "1.11", optional = true }
 
 [features]
+default = ["map"]
+
+# impl Diffable on `std::collections::BTreeMap` and `std::collections::HashMap`
+map = []
+
 # impl Diffable on `chrono::DateTime`
 chrono = ["dep:chrono"]
 

src/lib.rs

@@ -1,10 +1,11 @@
 #![doc = include_str!("../README.md")]
 
+use std::{marker::PhantomData, ops::Deref};
+
+#[cfg(feature = "map")]
 use std::{
     collections::{BTreeMap, HashMap},
     hash::Hash,
-    marker::PhantomData,
-    ops::Deref,
 };
 
 pub use difficient_macros::Diffable;
@@ -234,6 +235,7 @@ where
 
 #[derive(Debug, Clone, PartialEq)]
 #[cfg_attr(feature = "serde", derive(serde::Serialize))]
+#[cfg(feature = "map")]
 /// A generic type which represents the possible change-states of a Key-Value type
 /// (e.g. `HashMap`, `BTreeMap`)
 pub enum KvDiff<'a, T, U> {
@@ -270,6 +272,7 @@ impl_diffable_for_primitives! {
     String
 }
 
+#[cfg(feature = "map")]
 macro_rules! kv_map_impl {
     ($typ: ident, $bounds: ident) => {
         #[allow(
@@ -357,7 +360,10 @@ macro_rules! kv_map_impl {
     };
 }
 
+#[cfg(feature = "map")]
 kv_map_impl!(HashMap, Hash);
+
+#[cfg(feature = "map")]
 kv_map_impl!(BTreeMap, Ord);
 
 impl Diffable<'_> for () {

src/serde_visit.rs

@@ -4,7 +4,9 @@ use std::{
     hash::Hash,
 };
 
-use super::{AtomicDiff, DeepDiff, Id, KvDiff, Replace};
+use super::{AtomicDiff, DeepDiff, Id, Replace};
+#[cfg(feature = "map")]
+use super::KvDiff;
 use crate::PatchOnlyDiff;
 
 /// A trait that allows the user to extract information from a 'diff' type.
@@ -160,6 +162,7 @@ tuple_impl!(A 0, B 1, C 2);
 tuple_impl!(A 0, B 1);
 tuple_impl!(A 0);
 
+#[cfg(feature = "map")]
 macro_rules! kv_map_impl {
     ($typ: ident, $bounds: ident) => {
         #[allow(
@@ -196,7 +199,9 @@ macro_rules! kv_map_impl {
     };
 }
 
+#[cfg(feature = "map")]
 kv_map_impl!(HashMap, Hash);
+#[cfg(feature = "map")]
 kv_map_impl!(BTreeMap, Ord);
 
 #[cfg(test)]