Improve code generation of Ord and PartialOrd for the first and last variant

Author: daxpedda

src/test/basic.rs

@@ -220,14 +220,7 @@ fn enum_() -> Result<()> {
 	#[cfg(all(not(feature = "nightly"), feature = "safe"))]
 	let ord = quote! {
 		match self {
-			Test::A { field: ref __field } =>
-				match __other {
-					Test::B { } => ::core::cmp::Ordering::Less,
-					Test::C(ref __other_0) => ::core::cmp::Ordering::Less,
-					Test::D() => ::core::cmp::Ordering::Less,
-					Test::E => ::core::cmp::Ordering::Less,
-					_ => ::core::unreachable!("comparing variants yielded unexpected results"),
-				},
+			Test::A { field: ref __field } => ::core::cmp::Ordering::Less,
 			Test::B { } =>
 				match __other {
 					Test::A { field: ref __other_field } => ::core::cmp::Ordering::Greater,
@@ -252,14 +245,7 @@ fn enum_() -> Result<()> {
 					Test::E => ::core::cmp::Ordering::Less,
 					_ => ::core::unreachable!("comparing variants yielded unexpected results"),
 				},
-			Test::E =>
-				match __other {
-					Test::A { field: ref __other_field } => ::core::cmp::Ordering::Greater,
-					Test::B { } => ::core::cmp::Ordering::Greater,
-					Test::C(ref __other_0) => ::core::cmp::Ordering::Greater,
-					Test::D() => ::core::cmp::Ordering::Greater,
-					_ => ::core::unreachable!("comparing variants yielded unexpected results"),
-				},
+			Test::E => ::core::cmp::Ordering::Greater,
 		}
 	};
 	#[cfg(feature = "nightly")]
@@ -276,14 +262,7 @@ fn enum_() -> Result<()> {
 	#[cfg(all(not(feature = "nightly"), feature = "safe"))]
 	let partial_ord = quote! {
 		match self {
-			Test::A { field: ref __field } =>
-				match __other {
-					Test::B { } => ::core::option::Option::Some(::core::cmp::Ordering::Less),
-					Test::C(ref __other_0) => ::core::option::Option::Some(::core::cmp::Ordering::Less),
-					Test::D() => ::core::option::Option::Some(::core::cmp::Ordering::Less),
-					Test::E => ::core::option::Option::Some(::core::cmp::Ordering::Less),
-					_ => ::core::unreachable!("comparing variants yielded unexpected results"),
-				},
+			Test::A { field: ref __field } => ::core::option::Option::Some(::core::cmp::Ordering::Less),
 			Test::B { } =>
 				match __other {
 					Test::A { field: ref __other_field } => ::core::option::Option::Some(::core::cmp::Ordering::Greater),
@@ -308,14 +287,7 @@ fn enum_() -> Result<()> {
 					Test::E => ::core::option::Option::Some(::core::cmp::Ordering::Less),
 					_ => ::core::unreachable!("comparing variants yielded unexpected results"),
 				},
-			Test::E =>
-				match __other {
-					Test::A { field: ref __other_field } => ::core::option::Option::Some(::core::cmp::Ordering::Greater),
-					Test::B { } => ::core::option::Option::Some(::core::cmp::Ordering::Greater),
-					Test::C(ref __other_0) => ::core::option::Option::Some(::core::cmp::Ordering::Greater),
-					Test::D() => ::core::option::Option::Some(::core::cmp::Ordering::Greater),
-					_ => ::core::unreachable!("comparing variants yielded unexpected results"),
-				},
+			Test::E => ::core::option::Option::Some(::core::cmp::Ordering::Greater),
 		}
 	};
 

src/test/enum_.rs

@@ -136,16 +136,8 @@ fn two_data() -> Result<()> {
 	#[cfg(all(not(feature = "nightly"), feature = "safe"))]
 	let partial_ord = quote! {
 		match self {
-			Test::A(ref __0) =>
-				match __other {
-					Test::B(ref __other_0) => ::core::option::Option::Some(::core::cmp::Ordering::Less),
-					_ => #unreachable,
-				},
-			Test::B(ref __0) =>
-				match __other {
-					Test::A(ref __other_0) => ::core::option::Option::Some(::core::cmp::Ordering::Greater),
-					_ => #unreachable,
-				},
+			Test::A(ref __0) => ::core::option::Option::Some(::core::cmp::Ordering::Less),
+			Test::B(ref __0) => ::core::option::Option::Some(::core::cmp::Ordering::Greater),
 		}
 	};
 
@@ -228,16 +220,8 @@ fn unit() -> Result<()> {
 	#[cfg(all(not(feature = "nightly"), feature = "safe"))]
 	let partial_ord = quote! {
 		match self {
-			Test::A(ref __0) =>
-				match __other {
-					Test::B => ::core::option::Option::Some(::core::cmp::Ordering::Less),
-					_ => ::core::unreachable!("comparing variants yielded unexpected results"),
-				},
-			Test::B =>
-				match __other {
-					Test::A(ref __other_0) => ::core::option::Option::Some(::core::cmp::Ordering::Greater),
-					_ => ::core::unreachable!("comparing variants yielded unexpected results"),
-				},
+			Test::A(ref __0) => ::core::option::Option::Some(::core::cmp::Ordering::Less),
+			Test::B => ::core::option::Option::Some(::core::cmp::Ordering::Greater),
 		}
 	};
 
@@ -313,16 +297,8 @@ fn struct_unit() -> Result<()> {
 	#[cfg(all(not(feature = "nightly"), feature = "safe"))]
 	let partial_ord = quote! {
 		match self {
-			Test::A(ref __0) =>
-				match __other {
-					Test::B { } => ::core::option::Option::Some(::core::cmp::Ordering::Less),
-					_ => ::core::unreachable!("comparing variants yielded unexpected results"),
-				},
-			Test::B { } =>
-				match __other {
-					Test::A(ref __other_0) => ::core::option::Option::Some(::core::cmp::Ordering::Greater),
-					_ => ::core::unreachable!("comparing variants yielded unexpected results"),
-				},
+			Test::A(ref __0) => ::core::option::Option::Some(::core::cmp::Ordering::Less),
+			Test::B { } => ::core::option::Option::Some(::core::cmp::Ordering::Greater),
 		}
 	};
 
@@ -398,16 +374,8 @@ fn tuple_unit() -> Result<()> {
 	#[cfg(all(not(feature = "nightly"), feature = "safe"))]
 	let partial_ord = quote! {
 		match self {
-			Test::A(ref __0) =>
-				match __other {
-					Test::B() => ::core::option::Option::Some(::core::cmp::Ordering::Less),
-					_ => ::core::unreachable!("comparing variants yielded unexpected results"),
-				},
-			Test::B() =>
-				match __other {
-					Test::A(ref __other_0) => ::core::option::Option::Some(::core::cmp::Ordering::Greater),
-					_ => ::core::unreachable!("comparing variants yielded unexpected results"),
-				},
+			Test::A(ref __0) => ::core::option::Option::Some(::core::cmp::Ordering::Less),
+			Test::B() => ::core::option::Option::Some(::core::cmp::Ordering::Greater),
 		}
 	};
 

src/test/skip.rs

@@ -122,16 +122,8 @@ fn variants_empty() -> Result<()> {
 	#[cfg(all(not(feature = "nightly"), feature = "safe"))]
 	let ord = quote! {
 		match self {
-			Test::A(ref __0) =>
-				match __other {
-					Test::B (ref __other_0) => ::core::cmp::Ordering::Less,
-					_ => ::core::unreachable!("comparing variants yielded unexpected results"),
-				},
-			Test::B(ref __0) =>
-				match __other {
-					Test::A (ref __other_0) => ::core::cmp::Ordering::Greater,
-					_ => ::core::unreachable!("comparing variants yielded unexpected results"),
-				},
+			Test::A(ref __0) => ::core::cmp::Ordering::Less,
+			Test::B(ref __0) => ::core::cmp::Ordering::Greater,
 		}
 	};
 
@@ -190,16 +182,8 @@ fn variants_partly_empty() -> Result<()> {
 	#[cfg(all(not(feature = "nightly"), feature = "safe"))]
 	let ord = quote! {
 		match self {
-			Test::A(ref __0) =>
-				match __other {
-					Test::B (ref __other_0, ref __other_1) => ::core::cmp::Ordering::Less,
-					_ => ::core::unreachable!("comparing variants yielded unexpected results"),
-				},
-			Test::B(ref __0, ref __1) =>
-				match __other {
-					Test::A (ref __other_0) => ::core::cmp::Ordering::Greater,
-					_ => ::core::unreachable!("comparing variants yielded unexpected results"),
-				},
+			Test::A(ref __0) => ::core::cmp::Ordering::Less,
+			Test::B(ref __0, ref __1) => ::core::cmp::Ordering::Greater,
 		}
 	};
 

src/trait_/common_ord.rs

@@ -105,35 +105,48 @@ pub fn build_ord_signature(item: &Item, trait_: &DeriveTrait, body: &TokenStream
 				// other. The index for these variants is used to determine which
 				// `Ordering` to return.
 				for (index, variant) in variants.iter().enumerate() {
-					let mut arms = Vec::with_capacity(variants.len() - 1);
+					let pattern = &variant.self_pattern();
 
-					for (index_other, variant_other) in variants.iter().enumerate() {
-						// Make sure we aren't comparing the same variant with itself.
-						if index != index_other {
-							use std::cmp::Ordering::*;
+					// The first variant is always `Less` then everything.
+					if index == 0 {
+						different.push(quote! {
+							#pattern => #less,
+						})
+					}
+					// The last variant is always `Greater` then everything.
+					else if index == variants.len() - 1 {
+						different.push(quote! {
+							#pattern => #greater,
+						})
+					} else {
+						let mut arms = Vec::with_capacity(variants.len() - 1);
 
-							let ordering = match index.cmp(&index_other) {
-								Less => &less,
-								Equal => &equal,
-								Greater => &greater,
-							};
+						for (index_other, variant_other) in variants.iter().enumerate() {
+							// Make sure we aren't comparing the same variant with itself.
+							if index != index_other {
+								use std::cmp::Ordering::*;
 
-							let pattern = &variant_other.other_pattern();
+								let ordering = match index.cmp(&index_other) {
+									Less => &less,
+									Equal => &equal,
+									Greater => &greater,
+								};
 
-							arms.push(quote! {
-								#pattern => #ordering,
-							});
-						}
-					}
+								let pattern = &variant_other.other_pattern();
 
-					let pattern = &variant.self_pattern();
+								arms.push(quote! {
+									#pattern => #ordering,
+								});
+							}
+						}
 
-					different.push(quote! {
-						#pattern => match __other {
-							#(#arms)*
-							_ => ::core::unreachable!("comparing variants yielded unexpected results"),
-						},
-					});
+						different.push(quote! {
+							#pattern => match __other {
+								#(#arms)*
+								_ => ::core::unreachable!("comparing variants yielded unexpected results"),
+							},
+						});
+					}
 				}
 
 				quote! {