Implement ZeroizeOnDrop without Drop

CHANGELOG.md

@@ -5,6 +5,12 @@ 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
+- `no_drop` item-level option to `ZeroizeOnDrop` which does not implement
+  `Drop` but instead only asserts that every field implements `ZeroizeOnDrop`.
+
 ## [1.4.0] - 2025-05-01
 
 ### Added

README.md

@@ -238,9 +238,12 @@ If the `zeroize-on-drop` feature is enabled, it implements [`ZeroizeOnDrop`]
 and can be implemented without [`Zeroize`], otherwise it only implements
 [`Drop`] and requires [`Zeroize`] to be implemented.
 
-[`ZeroizeOnDrop`] has one option:
+[`ZeroizeOnDrop`] has two options:
 - `crate`: an item-level option which specifies a path to the [`zeroize`]
   crate in case of a re-export or rename.
+- `no_drop`: an item-level option which will not implement [`Drop`] but instead
+  only assert that every field implements [`ZeroizeOnDrop`]. Requires the
+  `zeroize-on-drop` feature.
 
 ```rust
 #[derive_where(ZeroizeOnDrop(crate = zeroize_))]

src/attr.rs

@@ -15,7 +15,7 @@ pub use self::{
 	default::Default,
 	field::FieldAttr,
 	incomparable::Incomparable,
-	item::{DeriveTrait, DeriveWhere, ItemAttr},
+	item::{DeriveWhere, ItemAttr},
 	skip::{Skip, SkipGroup},
 	variant::VariantAttr,
 };

src/attr/field.rs

@@ -4,7 +4,7 @@ use syn::{spanned::Spanned, Attribute, Meta, Result};
 
 use crate::{util::MetaListExt, DeriveWhere, Error, Skip, DERIVE_WHERE};
 #[cfg(feature = "zeroize")]
-use crate::{Trait, TraitImpl, ZeroizeFqs};
+use crate::{Trait, ZeroizeFqs};
 
 /// Attributes on field.
 #[derive(Default)]

src/attr/incomparable.rs

@@ -3,7 +3,7 @@
 use proc_macro2::Span;
 use syn::{spanned::Spanned, Meta, Result};
 
-use crate::{attr::DeriveTrait, DeriveWhere, Error};
+use crate::{trait_::DeriveTrait, DeriveWhere, Error};
 
 /// Stores if this variant should be incomparable when implementing
 /// [`PartialEq`] or [`PartialOrd`].

src/attr/item.rs

@@ -1,20 +1,17 @@
 //! [`Attribute`] parsing for items.
 
-use std::{borrow::Cow, ops::Deref};
+use std::borrow::Cow;
 
 use proc_macro2::Span;
 use syn::{
 	parse::{discouraged::Speculative, Parse, ParseStream},
 	punctuated::Punctuated,
 	spanned::Spanned,
-	Attribute, BoundLifetimes, Data, Ident, Meta, Path, PredicateType, Result, Token, TraitBound,
-	TraitBoundModifier, Type, TypeParamBound, TypePath, WhereClause, WherePredicate,
+	Attribute, BoundLifetimes, Data, Ident, Meta, PredicateType, Result, Token, Type, TypePath,
+	WhereClause, WherePredicate,
 };
 
-use crate::{
-	util::{self, MetaListExt},
-	Error, Incomparable, Item, Skip, SkipGroup, Trait, TraitImpl, DERIVE_WHERE,
-};
+use crate::{trait_::DeriveTrait, Error, Incomparable, Item, Skip, SkipGroup, Trait, DERIVE_WHERE};
 
 /// Attributes on item.
 #[derive(Default)]
@@ -259,7 +256,7 @@ impl DeriveWhere {
 	pub fn any_skip(&self) -> bool {
 		self.traits
 			.iter()
-			.any(|trait_| SkipGroup::trait_supported_by_skip_all(**trait_))
+			.any(|trait_| SkipGroup::trait_supported_by_skip_all(***trait_))
 	}
 
 	/// Create [`WhereClause`] for the given parameters.
@@ -353,172 +350,3 @@ impl Parse for Generic {
 		}
 	}
 }
-
-/// Trait to implement.
-#[derive(Eq, PartialEq)]
-pub enum DeriveTrait {
-	/// [`Clone`].
-	Clone,
-	/// [`Copy`].
-	Copy,
-	/// [`Debug`](std::fmt::Debug).
-	Debug,
-	/// [`Default`].
-	Default,
-	/// [`Eq`].
-	Eq,
-	/// [`Hash`](std::hash::Hash).
-	Hash,
-	/// [`Ord`].
-	Ord,
-	/// [`PartialEq`].
-	PartialEq,
-	/// [`PartialOrd`].
-	PartialOrd,
-	/// [`Zeroize`](https://docs.rs/zeroize/latest/zeroize/trait.Zeroize.html).
-	#[cfg(feature = "zeroize")]
-	Zeroize {
-		/// [`Zeroize`](https://docs.rs/zeroize/latest/zeroize/trait.Zeroize.html) path.
-		crate_: Option<Path>,
-	},
-	/// [`ZeroizeOnDrop`](https://docs.rs/zeroize/latest/zeroize/trait.ZeroizeOnDrop.html).
-	#[cfg(feature = "zeroize")]
-	ZeroizeOnDrop {
-		/// [`ZeroizeOnDrop`](https://docs.rs/zeroize/latest/zeroize/trait.ZeroizeOnDrop.html) path.
-		crate_: Option<Path>,
-	},
-}
-
-impl Deref for DeriveTrait {
-	type Target = Trait;
-
-	fn deref(&self) -> &Self::Target {
-		use DeriveTrait::*;
-
-		match self {
-			Clone => &Trait::Clone,
-			Copy => &Trait::Copy,
-			Debug => &Trait::Debug,
-			Default => &Trait::Default,
-			Eq => &Trait::Eq,
-			Hash => &Trait::Hash,
-			Ord => &Trait::Ord,
-			PartialEq => &Trait::PartialEq,
-			PartialOrd => &Trait::PartialOrd,
-			#[cfg(feature = "zeroize")]
-			Zeroize { .. } => &Trait::Zeroize,
-			#[cfg(feature = "zeroize")]
-			ZeroizeOnDrop { .. } => &Trait::ZeroizeOnDrop,
-		}
-	}
-}
-
-impl PartialEq<Trait> for &DeriveTrait {
-	fn eq(&self, other: &Trait) -> bool {
-		let trait_: &Trait = self;
-		trait_ == other
-	}
-}
-
-impl DeriveTrait {
-	/// Returns fully qualified [`Path`] for this trait.
-	pub fn path(&self) -> Path {
-		use DeriveTrait::*;
-
-		match self {
-			Clone => util::path_from_root_and_strs(self.crate_(), &["clone", "Clone"]),
-			Copy => util::path_from_root_and_strs(self.crate_(), &["marker", "Copy"]),
-			Debug => util::path_from_root_and_strs(self.crate_(), &["fmt", "Debug"]),
-			Default => util::path_from_root_and_strs(self.crate_(), &["default", "Default"]),
-			Eq => util::path_from_root_and_strs(self.crate_(), &["cmp", "Eq"]),
-			Hash => util::path_from_root_and_strs(self.crate_(), &["hash", "Hash"]),
-			Ord => util::path_from_root_and_strs(self.crate_(), &["cmp", "Ord"]),
-			PartialEq => util::path_from_root_and_strs(self.crate_(), &["cmp", "PartialEq"]),
-			PartialOrd => util::path_from_root_and_strs(self.crate_(), &["cmp", "PartialOrd"]),
-			#[cfg(feature = "zeroize")]
-			Zeroize { .. } => util::path_from_root_and_strs(self.crate_(), &["Zeroize"]),
-			#[cfg(feature = "zeroize")]
-			ZeroizeOnDrop { .. } => util::path_from_root_and_strs(self.crate_(), &["ZeroizeOnDrop"]),
-		}
-	}
-
-	/// Returns the path to the root crate for this trait.
-	pub fn crate_(&self) -> Path {
-		use DeriveTrait::*;
-
-		match self {
-			Clone => util::path_from_strs(&["core"]),
-			Copy => util::path_from_strs(&["core"]),
-			Debug => util::path_from_strs(&["core"]),
-			Default => util::path_from_strs(&["core"]),
-			Eq => util::path_from_strs(&["core"]),
-			Hash => util::path_from_strs(&["core"]),
-			Ord => util::path_from_strs(&["core"]),
-			PartialEq => util::path_from_strs(&["core"]),
-			PartialOrd => util::path_from_strs(&["core"]),
-			#[cfg(feature = "zeroize")]
-			Zeroize { crate_, .. } => {
-				if let Some(crate_) = crate_ {
-					crate_.clone()
-				} else {
-					util::path_from_strs(&["zeroize"])
-				}
-			}
-			#[cfg(feature = "zeroize")]
-			ZeroizeOnDrop { crate_, .. } => {
-				if let Some(crate_) = crate_ {
-					crate_.clone()
-				} else {
-					util::path_from_strs(&["zeroize"])
-				}
-			}
-		}
-	}
-
-	/// Returns where-clause bounds for the trait in respect of the item type.
-	fn where_bounds(&self, data: &Item) -> Punctuated<TypeParamBound, Token![+]> {
-		let mut list = Punctuated::new();
-
-		list.push(TypeParamBound::Trait(TraitBound {
-			paren_token: None,
-			modifier: TraitBoundModifier::None,
-			lifetimes: None,
-			path: self.path(),
-		}));
-
-		// Add bounds specific to the trait.
-		if let Some(bound) = self.additional_where_bounds(data) {
-			list.push(bound)
-		}
-
-		list
-	}
-
-	/// Create [`DeriveTrait`] from [`ParseStream`].
-	fn from_stream(span: Span, data: &Data, input: ParseStream) -> Result<(Span, Self)> {
-		match Meta::parse(input) {
-			Ok(meta) => {
-				let trait_ = Trait::from_path(meta.path())?;
-
-				if let Data::Union(_) = data {
-					// Make sure this `Trait` supports unions.
-					if !trait_.supports_union() {
-						return Err(Error::union(span));
-					}
-				}
-
-				match &meta {
-					Meta::Path(path) => Ok((path.span(), trait_.default_derive_trait())),
-					Meta::List(list) => {
-						let nested = list.parse_non_empty_nested_metas()?;
-
-						// This will return an error if no options are supported.
-						Ok((list.span(), trait_.parse_derive_trait(meta.span(), nested)?))
-					}
-					Meta::NameValue(name_value) => Err(Error::option_syntax(name_value.span())),
-				}
-			}
-			Err(error) => Err(Error::trait_syntax(error.span())),
-		}
-	}
-}

src/attr/skip.rs

@@ -4,7 +4,7 @@ use std::default::Default;
 
 use syn::{spanned::Spanned, Meta, Path, Result};
 
-use crate::{attr::DeriveTrait, util::MetaListExt, DeriveWhere, Error, Trait};
+use crate::{trait_::DeriveTrait, util::MetaListExt, DeriveWhere, Error, Trait};
 
 /// Stores what [`Trait`]s to skip this field or variant for.
 #[cfg_attr(test, derive(Debug))]

src/attr/zeroize_fqs.rs

@@ -2,7 +2,7 @@
 
 use syn::{spanned::Spanned, Meta, Result};
 
-use crate::{util::MetaListExt, DeriveWhere, Error, Trait, TraitImpl};
+use crate::{util::MetaListExt, DeriveWhere, Error, Trait};
 
 /// Stores if this field should use FQS to call [`Zeroize::zeroize`](https://docs.rs/zeroize/latest/zeroize/trait.Zeroize.html#tymethod.zeroize).
 #[derive(Default)]

src/input.rs

@@ -3,10 +3,13 @@
 use proc_macro2::Span;
 use syn::{DeriveInput, GenericParam, Generics, ImplGenerics, Result, TypeGenerics, WhereClause};
 
-#[cfg(feature = "zeroize")]
-use crate::DeriveTrait;
 #[cfg(not(feature = "nightly"))]
 use crate::Discriminant;
+#[cfg(feature = "zeroize")]
+use crate::{
+	trait_::{zeroize::Zeroize, zeroize_on_drop::ZeroizeOnDrop},
+	DeriveTrait,
+};
 use crate::{Data, DeriveWhere, Either, Error, Item, ItemAttr, Trait};
 
 /// Parsed input.
@@ -170,7 +173,7 @@ impl<'a> Input<'a> {
 				}
 
 				// Any field is skipped with a corresponding `Trait`.
-				if item.any_skip_trait(**trait_) {
+				if item.any_skip_trait(***trait_) {
 					continue;
 				}
 
@@ -181,9 +184,13 @@ impl<'a> Input<'a> {
 
 				#[cfg(feature = "zeroize")]
 				{
-					// `Zeroize(crate = ..)` or `ZeroizeOnDrop(crate = ..)` is used.
-					if let DeriveTrait::Zeroize { crate_: Some(_) }
-					| DeriveTrait::ZeroizeOnDrop { crate_: Some(_) } = *trait_
+					// `Zeroize(crate = ..)`, `ZeroizeOnDrop(crate = ..)` or
+					// `ZeroizeOnDrop(no_drop)` is used.
+					if let DeriveTrait::Zeroize(Zeroize { crate_: Some(_) })
+					| DeriveTrait::ZeroizeOnDrop(ZeroizeOnDrop {
+						crate_: Some(_), ..
+					})
+					| DeriveTrait::ZeroizeOnDrop(ZeroizeOnDrop { no_drop: true, .. }) = *trait_
 					{
 						continue;
 					}