Ord and PartialOrd derives do not specify ordering behavior types with multiple fields

[james7132]

Location

Derive macros for Ord and PartialOrd.

Summary

The derive macros for Ord and PartialOrd do not specify what the order of precedence it generates in the resulting implementation. This order matters, and makes reordering fields on a type with this derive a semver-incompatible breaking change.

Examples

#[derive(PartialEq, Eq, PartialOrd, Ord)]
pub struct MyStruct {
   field_1: u32,
   field_2: i32,
}

Does field_1 take precedence over field_2 when comparing two MyStructs?

#[derive(PartialEq, Eq, PartialOrd, Ord)]
pub enum MyEnum {
   Variant_1 {
     field_1: u32,
     field_2: i32,
   },
   Variant_2 {
     field_1: i32,
     field_2: u32,
   }
   Variant_3(MyStruct),
}

Do all Variant_1 come before or after Variant_2?

[asquared31415]

The trait docs specify the way that the derive works. These docs should probably be duplicated on the derive macro too.