Add Serde Support

.config/topic.dic

@@ -1,4 +1,4 @@
-19
+21
 ≥1
 APIs
 Changelog
@@ -11,6 +11,8 @@ FQS
 invariants
 io
 MSRV
+Serde
+Serde's
 std's
 struct/S
 TODO

.github/workflows/lint.yml

@@ -28,12 +28,16 @@ jobs:
             features: --features safe
           - channel: nightly
             features: --features nightly 
+          - channel: stable
+            features: --features serde
           - channel: stable
             features: --features zeroize
           - channel: stable
             features: --features zeroize-on-drop
           - channel: nightly
             features: --features safe,nightly
+          - channel: stable
+            features: --features safe,serde
           - channel: stable
             features: --features safe,zeroize
           - channel: stable
@@ -42,6 +46,12 @@ jobs:
             features: --features nightly,zeroize
           - channel: nightly
             features: --features nightly,zeroize-on-drop
+          - channel: nightly
+            features: --features nightly,serde
+          - channel: stable
+            features: --features serde,zeroize
+          - channel: stable
+            features: --features serde,zeroize-on-drop
           - channel: nightly
             features: --all-features
 

.github/workflows/test.yml

@@ -28,17 +28,23 @@ jobs:
         features:
           - ""
           - --features safe
+          - --features serde
           - --features zeroize
           - --features zeroize-on-drop
+          - --features safe,serde
           - --features safe,zeroize
           - --features safe,zeroize-on-drop
+          - --features serde,zeroize
+          - --features serde,zeroize-on-drop
         include:
           - rust: 1.57.0
             msrv: true
           - rust: nightly
             features: --features nightly
           - rust: nightly
             features: --features safe,nightly
+          - rust: nightly
+            features: --features nightly,serde
           - rust: nightly
             features: --features nightly,zeroize
           - rust: nightly
@@ -83,17 +89,23 @@ jobs:
         features:
           - ""
           - --features safe
+          - --features serde
           - --features zeroize
           - --features zeroize-on-drop
+          - --features safe,serde
           - --features safe,zeroize
           - --features safe,zeroize-on-drop
+          - --features serde,zeroize
+          - --features serde,zeroize-on-drop
         include:
           - rust: 1.57.0
             msrv: true
           - rust: nightly
             features: --features nightly
           - rust: nightly
             features: --features safe,nightly
+          - rust: nightly
+            features: --features nightly,serde
           - rust: nightly
             features: --features nightly,zeroize
           - rust: nightly
@@ -127,9 +139,9 @@ jobs:
       matrix:
         rust:
           - version: 1.57.0
-            features: safe,zeroize-on-drop
+            features: safe,serde_,zeroize-on-drop
           - version: stable
-            features: safe,zeroize-on-drop
+            features: safe,serde_,zeroize-on-drop
 
     steps:
       - name: Checkout

CHANGELOG.md

@@ -10,6 +10,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Added
 - `no_drop` item-level option to `ZeroizeOnDrop` which does not implement
   `Drop` but instead only asserts that every field implements `ZeroizeOnDrop`.
+- Support deriving Serde's `Deserialize` and `Serialize` trait via Serde's own
+  proc-macro.
+
+### Changed
+- Error messages now point to crate features instead of reporting traits as
+  unsupported.
 
 ### Fixed
 - Stop depending on unstable APIs for `Eq` for `ZeroizeOnDrop`.

Cargo.toml

@@ -23,6 +23,7 @@ proc-macro = true
 [features]
 nightly = []
 safe = []
+serde = []
 zeroize = []
 zeroize-on-drop = ["zeroize"]
 
@@ -41,8 +42,10 @@ syn = { version = "2", default-features = false, features = [
 [dev-dependencies]
 pretty_assertions = "1"
 rustversion = "1"
+serde_ = { package = "serde", version = "1", default-features = false, features = ["derive"] }
+serde_test = "1"
 trybuild = { version = "1.0.18", default-features = false }
-zeroize_ = { version = "1.5", package = "zeroize", default-features = false }
+zeroize_ = { package = "zeroize", version = "1.5", default-features = false }
 
 [package.metadata.docs.rs]
 all-features = true

README.md

@@ -200,6 +200,13 @@ assert!(!(StructExample <= StructExample));
 Note that it is not possible to use `incomparable` with [`Eq`] or [`Ord`] as
 that would break their invariants.
 
+### Serde `Deserialize` and `Serialize`
+
+Deriving [`Deserialize`] and [`Serialize`] works as expected. While
+derive-where does not offer any attribute options, regular `serde` attributes
+can be used. Derive-where will respect
+[`#[serde(crate = "...")]`](https://serde.rs/container-attrs.html#crate).
+
 ### `Zeroize` options
 
 `Zeroize` has two options:
@@ -259,11 +266,13 @@ The following traits can be derived with derive-where:
 - [`Copy`]
 - [`Debug`]
 - [`Default`]
+- [`Deserialize`]: Only available with the `serde` crate feature.
 - [`Eq`]
 - [`Hash`]
 - [`Ord`]
 - [`PartialEq`]
 - [`PartialOrd`]
+- [`Serialize`]: Only available with the `serde` crate feature.
 - [`Zeroize`]: Only available with the `zeroize` crate feature.
 - [`ZeroizeOnDrop`]: Only available with the `zeroize` crate feature. If the
   `zeroize-on-drop` feature is enabled, it implements [`ZeroizeOnDrop`],
@@ -352,12 +361,14 @@ conditions.
 [`core::intrinsics::discriminant_value`]: https://doc.rust-lang.org/core/intrinsics/fn.discriminant_value.html
 [`derive_where`]: https://docs.rs/derive-where/latest/derive_where/attr.derive_where.html
 [`Discriminant`]: https://doc.rust-lang.org/core/mem/struct.Discriminant.html
+[`Deserialize`]: https://docs.rs/serde/latest/serde/derive.Deserialize.html
 [`Drop`]: https://doc.rust-lang.org/core/ops/trait.Drop.html
 [`Eq`]: https://doc.rust-lang.org/core/cmp/trait.Eq.html
 [`i32`]: https://doc.rust-lang.org/core/primitive.i32.html
 [`isize`]: https://doc.rust-lang.org/core/primitive.isize.html
 [`Ord`]: https://doc.rust-lang.org/core/cmp/trait.Ord.html
 [`PartialEq`]: https://doc.rust-lang.org/core/cmp/trait.PartialEq.html
 [`PartialOrd`]: https://doc.rust-lang.org/core/cmp/trait.PartialOrd.html
+[`Serialize`]: https://docs.rs/serde/latest/serde/derive.Serialize.html
 [`transmute`]: https://doc.rust-lang.org/core/mem/fn.transmute.html
 [`unreachable`]: https://doc.rust-lang.org/core/macro.unreachable.html

src/attr.rs

@@ -1,5 +1,6 @@
 //! [`Attribute`](syn::Attribute) parsing for items, variants and fields.
 
+mod crate_;
 mod default;
 mod field;
 mod incomparable;
@@ -12,6 +13,7 @@ mod zeroize_fqs;
 #[cfg(feature = "zeroize")]
 pub use self::zeroize_fqs::ZeroizeFqs;
 pub use self::{
+	crate_::parse_crate,
 	default::Default,
 	field::FieldAttr,
 	incomparable::Incomparable,

src/attr/crate_.rs

@@ -0,0 +1,34 @@
+//! Parsing implementation for `#[derive_where(crate = ...)]`.
+
+use proc_macro2::Span;
+use syn::{spanned::Spanned, Expr, ExprLit, ExprPath, Lit, Meta, Path, Result};
+
+use crate::{util, Error, DERIVE_WHERE};
+
+/// Parses `#[derive_where(crate = ...)]`.
+pub fn parse_crate(meta: Meta) -> Result<(Path, Span)> {
+	if let Meta::NameValue(name_value) = meta {
+		let path = match &name_value.value {
+			Expr::Lit(ExprLit {
+				lit: Lit::Str(lit_str),
+				..
+			}) => match lit_str.parse::<Path>() {
+				Ok(path) => path,
+				Err(error) => return Err(Error::path(lit_str.span(), error)),
+			},
+			Expr::Path(ExprPath { path, .. }) => path.clone(),
+			_ => return Err(Error::option_syntax(name_value.value.span())),
+		};
+
+		if path == util::path_from_strs(&[DERIVE_WHERE]) {
+			Err(Error::path_unnecessary(
+				path.span(),
+				&format!("::{}", DERIVE_WHERE),
+			))
+		} else {
+			Ok((path, name_value.span()))
+		}
+	} else {
+		Err(Error::option_syntax(meta.span()))
+	}
+}

src/attr/item.rs

@@ -7,15 +7,17 @@ use syn::{
 	parse::{discouraged::Speculative, Parse, ParseStream},
 	punctuated::Punctuated,
 	spanned::Spanned,
-	Attribute, BoundLifetimes, Data, Ident, Meta, PredicateType, Result, Token, Type, TypePath,
-	WhereClause, WherePredicate,
+	Attribute, BoundLifetimes, Data, Ident, Meta, Path, PredicateType, Result, Token, Type,
+	TypePath, WhereClause, WherePredicate,
 };
 
 use crate::{trait_::DeriveTrait, Error, Incomparable, Item, Skip, SkipGroup, Trait, DERIVE_WHERE};
 
 /// Attributes on item.
 #[derive(Default)]
 pub struct ItemAttr {
+	/// Path to `derive_where` if set by `#[derive_where(crate = ...)]`.
+	pub crate_: Option<Path>,
 	/// [`Trait`]s to skip all fields for.
 	pub skip_inner: Skip,
 	/// Comparing item will yield `false` for [`PartialEq`] and [`None`] for
@@ -59,28 +61,29 @@ impl ItemAttr {
 									// Needs to be parsed after all traits are known.
 									incomparables.push(meta)
 								} else if meta.path().is_ident("crate") {
-									// Do nothing, we checked this before
-									// already.
+									let (path, _) = super::parse_crate(meta)
+										.expect("failed to parse previously parsed attribute");
+									self_.crate_ = Some(path);
 								}
 								// The list can have one item but still not be the `skip_inner`
 								// attribute, continue with parsing `DeriveWhere`.
 								else {
 									self_
 										.derive_wheres
-										.push(DeriveWhere::from_attr(span, data, attr)?);
+										.push(DeriveWhere::from_attr(attrs, span, data, attr)?);
 								}
 							}
 							_ => self_
 								.derive_wheres
-								.push(DeriveWhere::from_attr(span, data, attr)?),
+								.push(DeriveWhere::from_attr(attrs, span, data, attr)?),
 						}
 					}
 					// Anything list that isn't using `,` as separator, is because we expect
 					// `A, B; C`.
 					else {
 						self_
 							.derive_wheres
-							.push(DeriveWhere::from_attr(span, data, attr)?)
+							.push(DeriveWhere::from_attr(attrs, span, data, attr)?)
 					}
 				} else {
 					return Err(Error::option_syntax(attr.meta.span()));
@@ -93,6 +96,18 @@ impl ItemAttr {
 			return Err(Error::none(span));
 		}
 
+		// Check for `#[serde(...)]` attributes without `De/Serialize`.
+		#[cfg(feature = "serde")]
+		if !self_.derive_wheres.iter().any(|derive_where| {
+			derive_where.contains(Trait::Deserialize) | derive_where.contains(Trait::Serialize)
+		}) {
+			for attr in attrs {
+				if attr.path().is_ident("serde") {
+					return Err(Error::serde_without_serde(attr.span()));
+				}
+			}
+		}
+
 		// Merge `DeriveWhere`s with the same bounds.
 		self_
 			.derive_wheres
@@ -152,7 +167,7 @@ pub struct DeriveWhere {
 
 impl DeriveWhere {
 	/// Create [`DeriveWhere`] from [`Attribute`].
-	fn from_attr(span: Span, data: &Data, attr: &Attribute) -> Result<Self> {
+	fn from_attr(attrs: &[Attribute], span: Span, data: &Data, attr: &Attribute) -> Result<Self> {
 		attr.parse_args_with(|input: ParseStream| {
 			// Parse the attribute input, this should either be:
 			// - Comma separated traits.
@@ -169,7 +184,7 @@ impl DeriveWhere {
 				// Start with parsing a trait.
 				// Not checking for duplicates here, we do that after merging `derive_where`s
 				// with the same bounds.
-				let (span, trait_) = DeriveTrait::from_stream(span, data, input)?;
+				let (span, trait_) = DeriveTrait::from_stream(attrs, span, data, input)?;
 				spans.push(span);
 				traits.push(trait_);
 

src/attr/skip.rs

@@ -270,6 +270,8 @@ impl SkipGroup {
 			| Trait::Ord
 			| Trait::PartialEq
 			| Trait::PartialOrd => true,
+			#[cfg(feature = "serde")]
+			Trait::Deserialize | Trait::Serialize => false,
 			#[cfg(feature = "zeroize")]
 			Trait::Zeroize | Trait::ZeroizeOnDrop => true,
 		}