skip(Clone)

CHANGELOG.md

@@ -5,6 +5,13 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [Unreleased]
+
+### Added
+- Allow skipping fields for `Clone`, calling `Default::default()` instead.
+  **Note:** `Clone` is excluded from blanket skipping and can only be used with
+  selective skipping to avoid this being a breaking change.
+
 ## [1.3.0] - 2025-04-21
 
 ### Added

README.md

@@ -144,6 +144,7 @@ Selective skipping of fields for certain traits is also an option, both in
 `skip` and `skip_inner`. To prevent breaking invariants defined for these
 traits, some of them can only be skipped in groups. The following groups are
 available:
+- [`Clone`]: Uses [`Default`] instead of [`Clone`].
 - [`Debug`]
 - `EqHashOrd`: Skips [`Eq`], [`Hash`], [`Ord`], [`PartialOrd`] and
   [`PartialEq`].

src/attr/item.rs

@@ -259,7 +259,7 @@ impl DeriveWhere {
 	pub fn any_skip(&self) -> bool {
 		self.traits
 			.iter()
-			.any(|trait_| SkipGroup::trait_supported(**trait_))
+			.any(|trait_| SkipGroup::trait_supported_by_skip_all(**trait_))
 	}
 
 	/// Create [`WhereClause`] for the given parameters.

src/attr/skip.rs

@@ -4,7 +4,7 @@ use std::default::Default;
 
 use syn::{spanned::Spanned, Meta, Path, Result};
 
-use crate::{util::MetaListExt, DeriveWhere, Error, Trait};
+use crate::{attr::DeriveTrait, util::MetaListExt, DeriveWhere, Error, Trait};
 
 /// Stores what [`Trait`]s to skip this field or variant for.
 #[cfg_attr(test, derive(Debug))]
@@ -101,6 +101,18 @@ impl Skip {
 					if let Meta::Path(path) = nested_meta {
 						let skip_group = SkipGroup::from_path(path)?;
 
+						if skip_group == SkipGroup::Clone
+							&& derive_wheres.iter().any(|derive_where| {
+								derive_where
+									.traits
+									.iter()
+									.any(|trait_| trait_ == &DeriveTrait::Copy)
+							}) {
+							return Err(Error::unable_to_skip_clone_while_deriving_copy(
+								path.span(),
+							));
+						}
+
 						// Don't allow to skip the same trait twice.
 						if traits.contains(&skip_group) {
 							return Err(Error::option_skip_duplicate(
@@ -144,7 +156,7 @@ impl Skip {
 	pub fn trait_skipped(&self, trait_: Trait) -> bool {
 		match self {
 			Skip::None => false,
-			Skip::All => SkipGroup::trait_supported(trait_),
+			Skip::All => SkipGroup::trait_supported_by_skip_all(trait_),
 			Skip::Traits(skip_groups) => skip_groups
 				.iter()
 				.any(|skip_group| skip_group.traits().any(|this_trait| this_trait == trait_)),
@@ -166,6 +178,8 @@ impl Skip {
 #[derive(Clone, Copy, Eq, PartialEq)]
 #[cfg_attr(test, derive(Debug))]
 pub enum SkipGroup {
+	/// [`Clone`].
+	Clone,
 	/// [`Debug`].
 	Debug,
 	/// [`Eq`], [`Hash`], [`Ord`], [`PartialEq`] and [`PartialOrd`].
@@ -185,6 +199,7 @@ impl SkipGroup {
 			use SkipGroup::*;
 
 			match ident.to_string().as_str() {
+				"Clone" => Ok(Clone),
 				"Debug" => Ok(Debug),
 				"EqHashOrd" => Ok(EqHashOrd),
 				"Hash" => Ok(Hash),
@@ -202,6 +217,7 @@ impl SkipGroup {
 	/// messages.
 	const fn as_str(self) -> &'static str {
 		match self {
+			Self::Clone => "Clone",
 			Self::Debug => "Debug",
 			Self::EqHashOrd => "EqHashOrd",
 			Self::Hash => "Hash",
@@ -213,6 +229,9 @@ impl SkipGroup {
 	/// [`Trait`]s supported by this group.
 	fn traits(self) -> impl Iterator<Item = Trait> {
 		match self {
+			Self::Clone => [Some(Trait::Clone), None, None, None, None]
+				.into_iter()
+				.flatten(),
 			Self::Debug => [Some(Trait::Debug), None, None, None, None]
 				.into_iter()
 				.flatten(),
@@ -242,7 +261,7 @@ impl SkipGroup {
 	}
 
 	/// Returns `true` if [`Trait`] is supported by any group.
-	pub fn trait_supported(trait_: Trait) -> bool {
+	pub fn trait_supported_by_skip_all(trait_: Trait) -> bool {
 		match trait_ {
 			Trait::Clone | Trait::Copy | Trait::Default => false,
 			Trait::Debug

src/data.rs

@@ -311,7 +311,7 @@ impl<'a> Data<'a> {
 	}
 
 	/// Returns `true` if all fields are skipped with that [`Trait`].
-	fn skip(&self, trait_: Trait) -> bool {
+	pub fn skip(&self, trait_: Trait) -> bool {
 		self.skip_inner.trait_skipped(trait_)
 			|| match self.fields() {
 				Either::Left(fields) => fields.skip(trait_),

src/error.rs

@@ -277,6 +277,11 @@ impl Error {
 		)
 	}
 
+	/// Unsupported `skip(Clone)` while deriving copy.
+	pub fn unable_to_skip_clone_while_deriving_copy(skip_clone: Span) -> syn::Error {
+		syn::Error::new(skip_clone, "Cannot skip `Clone` while deriving `Copy`")
+	}
+
 	/// List of available [`Trait`](crate::Trait)s.
 	fn trait_list() -> String {
 		[
@@ -300,6 +305,7 @@ impl Error {
 	/// List of available [`SkipGroup`](crate::SkipGroup)s.
 	fn skip_group_list() -> String {
 		[
+			"Clone",
 			"Debug",
 			"EqHashOrd",
 			"Hash",

src/lib.rs

@@ -170,6 +170,7 @@
 //! `skip` and `skip_inner`. To prevent breaking invariants defined for these
 //! traits, some of them can only be skipped in groups. The following groups are
 //! available:
+//! - [`Clone`]: Uses [`Default`] instead of [`Clone`].
 //! - [`Debug`]
 //! - `EqHashOrd`: Skips [`Eq`], [`Hash`], [`Ord`], [`PartialOrd`] and
 //!   [`PartialEq`].

src/test/bound.rs

@@ -18,7 +18,7 @@ fn bound() -> Result<()> {
 				#[inline]
 				fn clone(&self) -> Self {
 					match self {
-						Test(ref __field_0, ref __field_1) => Test(::core::clone::Clone::clone(__field_0), ::core::clone::Clone::clone(__field_1)),
+						Test(ref __field_0, ref __field_1) => Test { 0: ::core::clone::Clone::clone(__field_0), 1: ::core::clone::Clone::clone(__field_1) },
 					}
 				}
 			}
@@ -48,7 +48,7 @@ fn bound_multiple() -> Result<()> {
 				#[inline]
 				fn clone(&self) -> Self {
 					match self {
-						Test(ref __field_0, ref __field_1) => Test(::core::clone::Clone::clone(__field_0), ::core::clone::Clone::clone(__field_1)),
+						Test(ref __field_0, ref __field_1) => Test{ 0: ::core::clone::Clone::clone(__field_0), 1: ::core::clone::Clone::clone(__field_1) },
 					}
 				}
 			}
@@ -78,7 +78,7 @@ fn custom_bound() -> Result<()> {
 				#[inline]
 				fn clone(&self) -> Self {
 					match self {
-						Test(ref __field_0) => Test(::core::clone::Clone::clone(__field_0)),
+						Test(ref __field_0) => Test { 0: ::core::clone::Clone::clone(__field_0) },
 					}
 				}
 			}
@@ -103,7 +103,7 @@ fn where_() -> Result<()> {
 				#[inline]
 				fn clone(&self) -> Self {
 					match self {
-						Test(ref __field_0, ref __field_1) => Test(::core::clone::Clone::clone(__field_0), ::core::clone::Clone::clone(__field_1)),
+						Test(ref __field_0, ref __field_1) => Test { 0: ::core::clone::Clone::clone(__field_0), 1: ::core::clone::Clone::clone(__field_1) },
 					}
 				}
 			}
@@ -128,7 +128,10 @@ fn for_lifetime() -> Result<()> {
 				#[inline]
 				fn clone(&self) -> Self {
 					match self {
-						Test(ref __field_0, ref __field_1) => Test(::core::clone::Clone::clone(__field_0), ::core::clone::Clone::clone(__field_1)),
+						Test(ref __field_0, ref __field_1) => Test {
+							0: ::core::clone::Clone::clone(__field_0),
+							1: ::core::clone::Clone::clone(__field_1)
+						},
 					}
 				}
 			}
@@ -151,7 +154,7 @@ fn associated_type() -> Result<()> {
 				#[inline]
 				fn clone(&self) -> Self {
 					match self {
-						Test(ref __field_0) => Test(::core::clone::Clone::clone(__field_0)),
+						Test(ref __field_0) => Test { 0: ::core::clone::Clone::clone(__field_0) },
 					}
 				}
 			}
@@ -174,7 +177,7 @@ fn associated_type_custom_bound() -> Result<()> {
 				#[inline]
 				fn clone(&self) -> Self {
 					match self {
-						Test(ref __field_0) => Test(::core::clone::Clone::clone(__field_0)),
+						Test(ref __field_0) => Test { 0: ::core::clone::Clone::clone(__field_0) },
 					}
 				}
 			}
@@ -197,7 +200,7 @@ fn check_trait_bounds() -> Result<()> {
 				#[inline]
 				fn clone(&self) -> Self {
 					match self {
-						Test(ref __field_0, ref __field_1) => Test(::core::clone::Clone::clone(__field_0), ::core::clone::Clone::clone(__field_1)),
+						Test(ref __field_0, ref __field_1) => Test { 0: ::core::clone::Clone::clone(__field_0), 1: ::core::clone::Clone::clone(__field_1) },
 					}
 				}
 			}
@@ -333,7 +336,7 @@ fn check_multiple_trait_bounds() -> Result<()> {
 				#[inline]
 				fn clone(&self) -> Self {
 					match self {
-						Test(ref __field_0, ref __field_1) => Test(::core::clone::Clone::clone(__field_0), ::core::clone::Clone::clone(__field_1)),
+						Test(ref __field_0, ref __field_1) => Test { 0: ::core::clone::Clone::clone(__field_0), 1: ::core::clone::Clone::clone(__field_1) },
 					}
 				}
 			}

src/test/clone.rs

@@ -26,6 +26,54 @@ fn struct_() -> Result<()> {
 	)
 }
 
+#[test]
+fn skip_inner() -> Result<()> {
+	test_derive(
+		quote! {
+			#[derive_where(Clone)]
+			#[derive_where(skip_inner(Clone))]
+			struct Test<T> {
+				field: std::marker::PhantomData<T>,
+			}
+		},
+		quote! {
+			#[automatically_derived]
+			impl<T> ::core::clone::Clone for Test<T> {
+				#[inline]
+				fn clone(&self) -> Self {
+					match self {
+						Test { field: ref __field_field } => Test { field: ::core::default::Default::default() },
+					}
+				}
+			}
+		},
+	)
+}
+
+#[test]
+fn skip_field() -> Result<()> {
+	test_derive(
+		quote! {
+			#[derive_where(Clone)]
+			struct Test<T> {
+				#[derive_where(skip(Clone))]
+				field: std::marker::PhantomData<T>,
+			}
+		},
+		quote! {
+			#[automatically_derived]
+			impl<T> ::core::clone::Clone for Test<T> {
+				#[inline]
+				fn clone(&self) -> Self {
+					match self {
+						Test { field: ref __field_field } => Test { field: ::core::default::Default::default() },
+					}
+				}
+			}
+		},
+	)
+}
+
 #[test]
 fn tuple() -> Result<()> {
 	test_derive(
@@ -39,7 +87,7 @@ fn tuple() -> Result<()> {
 				#[inline]
 				fn clone(&self) -> Self {
 					match self {
-						Test(ref __field_0) => Test(::core::clone::Clone::clone(__field_0)),
+						Test(ref __field_0) => Test { 0: ::core::clone::Clone::clone(__field_0) },
 					}
 				}
 			}
@@ -68,8 +116,8 @@ fn enum_() -> Result<()> {
 					match self {
 						Test::A { field: ref __field_field } => Test::A { field: ::core::clone::Clone::clone(__field_field) },
 						Test::B { } => Test::B { },
-						Test::C(ref __field_0) => Test::C(::core::clone::Clone::clone(__field_0)),
-						Test::D() => Test::D(),
+						Test::C(ref __field_0) => Test::C { 0: ::core::clone::Clone::clone(__field_0) },
+						Test::D() => Test::D { },
 						Test::E => Test::E,
 					}
 				}

src/trait_/clone.rs

@@ -5,7 +5,8 @@ use quote::quote;
 use syn::{TraitBound, TraitBoundModifier, TypeParamBound};
 
 use crate::{
-	Data, DataType, DeriveTrait, DeriveWhere, Item, SimpleType, SplitGenerics, Trait, TraitImpl,
+	data::Field, Data, DataType, DeriveTrait, DeriveWhere, Item, SimpleType, SplitGenerics, Trait,
+	TraitImpl,
 };
 
 /// Dummy-struct implement [`Trait`] for [`Clone`](trait@std::clone::Clone).
@@ -99,25 +100,26 @@ impl TraitImpl for Clone {
 		}
 
 		match data.simple_type() {
-			SimpleType::Struct(fields) => {
+			SimpleType::Struct(fields) | SimpleType::Tuple(fields) => {
 				let self_pattern = &fields.self_pattern;
 				let item_path = &data.path;
-				let self_ident = data.iter_self_ident(**trait_);
-				let fields = data.iter_field_ident(**trait_);
 				let trait_path = trait_.path();
+				let default_path = DeriveTrait::Default.path();
 
-				quote! {
-					#self_pattern => #item_path { #(#fields: #trait_path::clone(#self_ident)),* },
-				}
-			}
-			SimpleType::Tuple(fields) => {
-				let self_pattern = &fields.self_pattern;
-				let item_path = &data.path;
-				let self_ident = data.iter_self_ident(**trait_);
-				let trait_path = trait_.path();
+				let fields = fields.fields.iter().map(
+					|field @ Field {
+					     self_ident, member, ..
+					 }| {
+						if field.skip(Trait::Clone) || data.skip(Trait::Clone) {
+							quote!(#member: #default_path::default())
+						} else {
+							quote!(#member: #trait_path::clone(#self_ident))
+						}
+					},
+				);
 
 				quote! {
-					#self_pattern => #item_path(#(#trait_path::clone(#self_ident)),*),
+					#self_pattern => #item_path { #(#fields),* },
 				}
 			}
 			SimpleType::Unit(pattern) => {

tests/skip/field_trait.rs

@@ -4,7 +4,8 @@ use std::cmp::Ordering;
 use derive_where::derive_where;
 
 use crate::util::{
-	self, AssertDebug, AssertHash, AssertOrd, AssertPartialEq, AssertPartialOrd, Wrapper,
+	self, AssertClone, AssertDebug, AssertHash, AssertOrd, AssertPartialEq, AssertPartialOrd,
+	NonTrait, Wrapper,
 };
 
 #[test]
@@ -19,6 +20,18 @@ fn debug() {
 	assert_eq!(format!("{:?}", test_1), "Test");
 }
 
+#[test]
+fn clone() {
+	#[derive_where(Clone)]
+	struct Test<T>(#[derive_where(skip(Clone))] NonTrait<T>);
+
+	let test_1 = Test(42.into());
+
+	let _ = AssertClone(&test_1);
+
+	assert_eq!(test_1.clone().0.data(), 0)
+}
+
 #[test]
 fn hash() {
 	#[derive_where(Hash)]