Improve codegen for enums (#80)

Author: daxpedda

CHANGELOG.md

@@ -5,6 +5,14 @@ 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]
+
+### Changed
+- Use safe casting in `PartialOrd` and `Ord` implementations in more cases when
+  possible.
+- Avoid unnecessarily validating the discriminant type of enums with C
+  representations in some cases.
+
 ## [1.2.4] - 2023-09-01
 
 ### Fixed

src/test/discriminant.rs

@@ -386,6 +386,54 @@ fn repr_c() -> Result<()> {
 	)
 }
 
+#[test]
+fn repr_c_without_discriminant() -> Result<()> {
+	#[cfg(feature = "nightly")]
+	let partial_ord = quote! {
+		::core::cmp::PartialOrd::partial_cmp(
+			&::core::intrinsics::discriminant_value(self),
+			&::core::intrinsics::discriminant_value(__other),
+		)
+	};
+	#[cfg(not(feature = "nightly"))]
+	let partial_ord = quote! {
+		fn __discriminant(__this: &Test) -> isize {
+			match __this {
+				Test::A => 0,
+				Test::B => 1,
+				Test::C => 2
+			}
+		}
+
+		::core::cmp::PartialOrd::partial_cmp(&__discriminant(self), &__discriminant(__other))
+	};
+
+	test_derive(
+		quote! {
+			#[derive_where(PartialOrd)]
+			#[repr(C)]
+			enum Test {
+				A,
+				B,
+				#[derive_where(incomparable)]
+				C,
+			}
+		},
+		quote! {
+			impl ::core::cmp::PartialOrd for Test {
+				#[inline]
+				fn partial_cmp(&self, __other: &Self) -> ::core::option::Option<::core::cmp::Ordering> {
+					if ::core::matches!(self, Test::C) || ::core::matches!(__other, Test::C) {
+						return ::core::option::Option::None;
+					}
+
+					#partial_ord
+				}
+			}
+		},
+	)
+}
+
 #[test]
 fn repr_c_clone() -> Result<()> {
 	#[cfg(feature = "nightly")]
@@ -440,6 +488,57 @@ fn repr_c_clone() -> Result<()> {
 	)
 }
 
+#[test]
+fn repr_c_clone_without_discriminant() -> Result<()> {
+	#[cfg(feature = "nightly")]
+	let partial_ord = quote! {
+		::core::cmp::PartialOrd::partial_cmp(
+			&::core::intrinsics::discriminant_value(self),
+			&::core::intrinsics::discriminant_value(__other),
+		)
+	};
+	#[cfg(not(feature = "nightly"))]
+	let partial_ord = quote! {
+		::core::cmp::PartialOrd::partial_cmp(&(::core::clone::Clone::clone(self) as isize), &(::core::clone::Clone::clone(__other) as isize))
+	};
+
+	test_derive(
+		quote! {
+			#[derive_where(Clone, PartialOrd)]
+			#[repr(C)]
+			enum Test {
+				A,
+				B,
+				#[derive_where(incomparable)]
+				C,
+			}
+		},
+		quote! {
+			impl ::core::clone::Clone for Test {
+				#[inline]
+				fn clone(&self) -> Self {
+					match self {
+						Test::A => Test::A,
+						Test::B => Test::B,
+						Test::C => Test::C,
+					}
+				}
+			}
+
+			impl ::core::cmp::PartialOrd for Test {
+				#[inline]
+				fn partial_cmp(&self, __other: &Self) -> ::core::option::Option<::core::cmp::Ordering> {
+					if ::core::matches!(self, Test::C) || ::core::matches!(__other, Test::C) {
+						return ::core::option::Option::None;
+					}
+
+					#partial_ord
+				}
+			}
+		},
+	)
+}
+
 #[test]
 fn repr_c_copy() -> Result<()> {
 	#[cfg(feature = "nightly")]
@@ -485,6 +584,48 @@ fn repr_c_copy() -> Result<()> {
 	)
 }
 
+#[test]
+fn repr_c_copy_without_discriminant() -> Result<()> {
+	#[cfg(feature = "nightly")]
+	let partial_ord = quote! {
+		::core::cmp::PartialOrd::partial_cmp(
+			&::core::intrinsics::discriminant_value(self),
+			&::core::intrinsics::discriminant_value(__other),
+		)
+	};
+	#[cfg(not(feature = "nightly"))]
+	let partial_ord = quote! {
+		::core::cmp::PartialOrd::partial_cmp(&(*self as isize), &(*__other as isize))
+	};
+
+	test_derive(
+		quote! {
+			#[derive_where(Copy, PartialOrd)]
+			#[repr(C)]
+			enum Test {
+				A,
+				B,
+				#[derive_where(incomparable)]
+				C,
+			}
+		},
+		quote! {
+			impl ::core::marker::Copy for Test { }
+
+			impl ::core::cmp::PartialOrd for Test {
+				#[inline]
+				fn partial_cmp(&self, __other: &Self) -> ::core::option::Option<::core::cmp::Ordering> {
+					if ::core::matches!(self, Test::C) || ::core::matches!(__other, Test::C) {
+						return ::core::option::Option::None;
+					}
+
+					#partial_ord
+				}
+			}
+		},
+	)
+}
+
 #[test]
 fn repr_c_reverse() -> Result<()> {
 	#[cfg(feature = "nightly")]
@@ -1111,14 +1252,7 @@ fn repr_clone() -> Result<()> {
 			&::core::intrinsics::discriminant_value(__other),
 		)
 	};
-	#[cfg(not(any(feature = "nightly", feature = "safe")))]
-	let partial_ord = quote! {
-		::core::cmp::PartialOrd::partial_cmp(
-			&unsafe { *<*const _>::from(self).cast::<u64>() },
-			&unsafe { *<*const _>::from(__other).cast::<u64>() },
-		)
-	};
-	#[cfg(all(not(feature = "nightly"), feature = "safe"))]
+	#[cfg(not(feature = "nightly"))]
 	let partial_ord = quote! {
 		::core::cmp::PartialOrd::partial_cmp(&(::core::clone::Clone::clone(self) as u64), &(::core::clone::Clone::clone(__other) as u64))
 	};
@@ -1169,14 +1303,7 @@ fn repr_copy() -> Result<()> {
 			&::core::intrinsics::discriminant_value(__other),
 		)
 	};
-	#[cfg(not(any(feature = "nightly", feature = "safe")))]
-	let partial_ord = quote! {
-		::core::cmp::PartialOrd::partial_cmp(
-			&unsafe { *<*const _>::from(self).cast::<u64>() },
-			&unsafe { *<*const _>::from(__other).cast::<u64>() },
-		)
-	};
-	#[cfg(all(not(feature = "nightly"), feature = "safe"))]
+	#[cfg(not(feature = "nightly"))]
 	let partial_ord = quote! {
 		::core::cmp::PartialOrd::partial_cmp(&(*self as u64), &(*__other as u64))
 	};

src/trait_/common_ord.rs

@@ -140,7 +140,12 @@ pub fn build_ord_signature(
 							unreachable!("we should only generate this code with multiple variants")
 						}
 						Discriminant::Unit { c } => {
-							let validate_c = c.then(|| {
+							// C validation is only needed if custom discriminants are defined.
+							let validate_c = (*c
+								&& variants
+									.iter()
+									.any(|variant| variant.discriminant.is_some()))
+							.then(|| {
 								quote! {
 									#[repr(C)]
 									enum EnsureReprCIsIsize {
@@ -171,7 +176,6 @@ pub fn build_ord_signature(
 						Discriminant::Data => build_discriminant_order(
 							None, None, item, generics, variants, &path, &method,
 						),
-						#[cfg(feature = "safe")]
 						Discriminant::UnitRepr(repr) => {
 							if traits.iter().any(|trait_| trait_ == Trait::Copy) {
 								quote! {
@@ -183,19 +187,29 @@ pub fn build_ord_signature(
 									#path::#method(&(#clone::clone(self) as #repr), &(#clone::clone(__other) as #repr))
 								}
 							} else {
-								build_discriminant_order(
+								#[cfg(feature = "safe")]
+								let body_else = build_discriminant_order(
 									Some(*repr),
 									None,
 									item,
 									generics,
 									variants,
 									&path,
 									&method,
-								)
+								);
+								#[cfg(not(feature = "safe"))]
+								let body_else = quote! {
+									#path::#method(
+										&unsafe { *<*const _>::from(self).cast::<#repr>() },
+										&unsafe { *<*const _>::from(__other).cast::<#repr>() },
+									)
+								};
+
+								body_else
 							}
 						}
 						#[cfg(not(feature = "safe"))]
-						Discriminant::UnitRepr(repr) | Discriminant::DataRepr(repr) => {
+						Discriminant::DataRepr(repr) => {
 							quote! {
 								#path::#method(
 									&unsafe { *<*const _>::from(self).cast::<#repr>() },