Specialize PartialEq for Option<newtype>

Author: clubby789

compiler/rustc_ast/src/lib.rs

@@ -15,6 +15,7 @@
 #![feature(if_let_guard)]
 #![feature(let_chains)]
 #![feature(min_specialization)]
+#![feature(spec_option_partial_eq)]
 #![feature(negative_impls)]
 #![feature(slice_internals)]
 #![feature(stmt_expr_attributes)]

compiler/rustc_borrowck/src/lib.rs

@@ -6,6 +6,7 @@
 #![feature(min_specialization)]
 #![feature(never_type)]
 #![feature(rustc_attrs)]
+#![feature(spec_option_partial_eq)]
 #![feature(stmt_expr_attributes)]
 #![feature(trusted_step)]
 #![feature(try_blocks)]

compiler/rustc_data_structures/src/lib.rs

@@ -13,6 +13,7 @@
 #![feature(cell_leak)]
 #![feature(control_flow_enum)]
 #![feature(extend_one)]
+#![feature(spec_option_partial_eq)]
 #![feature(hash_raw_entry)]
 #![feature(hasher_prefixfree_extras)]
 #![feature(maybe_uninit_uninit_array)]

compiler/rustc_hir/src/lib.rs

@@ -9,6 +9,7 @@
 #![feature(never_type)]
 #![feature(rustc_attrs)]
 #![feature(variant_count)]
+#![feature(spec_option_partial_eq)]
 #![recursion_limit = "256"]
 #![deny(rustc::untranslatable_diagnostic)]
 #![deny(rustc::diagnostic_outside_of_impl)]

compiler/rustc_hir_analysis/src/lib.rs

@@ -65,6 +65,7 @@ This API is completely unstable and subject to change.
 #![feature(is_sorted)]
 #![feature(iter_intersperse)]
 #![feature(let_chains)]
+#![feature(spec_option_partial_eq)]
 #![feature(min_specialization)]
 #![feature(never_type)]
 #![feature(once_cell)]

compiler/rustc_hir_typeck/src/lib.rs

@@ -3,6 +3,7 @@
 #![feature(try_blocks)]
 #![feature(never_type)]
 #![feature(min_specialization)]
+#![feature(spec_option_partial_eq)]
 #![feature(control_flow_enum)]
 #![feature(drain_filter)]
 #![allow(rustc::potential_query_instability)]

compiler/rustc_index/src/lib.rs

@@ -6,6 +6,7 @@
 #![feature(new_uninit)]
 #![feature(step_trait)]
 #![feature(stmt_expr_attributes)]
+#![feature(spec_option_partial_eq)]
 #![feature(test)]
 
 pub mod bit_set;

compiler/rustc_infer/src/lib.rs

@@ -19,6 +19,7 @@
 #![feature(extend_one)]
 #![feature(let_chains)]
 #![feature(if_let_guard)]
+#![feature(spec_option_partial_eq)]
 #![feature(min_specialization)]
 #![feature(never_type)]
 #![feature(try_blocks)]

compiler/rustc_lint/src/lib.rs

@@ -34,6 +34,7 @@
 #![feature(iter_intersperse)]
 #![feature(iter_order_by)]
 #![feature(let_chains)]
+#![feature(spec_option_partial_eq)]
 #![feature(min_specialization)]
 #![feature(never_type)]
 #![recursion_limit = "256"]

compiler/rustc_macros/src/newtype.rs

@@ -192,6 +192,30 @@ impl Parse for Newtype {
                 }
             }
         };
+        let spec_partial_eq_impl = if let Lit::Int(max) = &max {
+            if let Ok(max_val) = max.base10_parse::<u32>() {
+                quote! {
+                    impl core::option::SpecOptionPartialEq for #name {
+                        #[inline]
+                        fn eq(l: &Option<Self>, r: &Option<Self>) -> bool {
+                            if #max_val < u32::MAX {
+                                l.map(|i| i.private).unwrap_or(#max_val+1) == r.map(|i| i.private).unwrap_or(#max_val+1)
+                            } else {
+                                match (l, r) {
+                                    (Some(l), Some(r)) => r == l,
+                                    (None, None) => true,
+                                    _ => false
+                                }
+                            }
+                        }
+                    }
+                }
+            } else {
+                quote! {}
+            }
+        } else {
+            quote! {}
+        };
 
         Ok(Self(quote! {
             #(#attrs)*
@@ -293,6 +317,8 @@ impl Parse for Newtype {
 
             #step
 
+            #spec_partial_eq_impl
+
             impl From<#name> for u32 {
                 #[inline]
                 fn from(v: #name) -> u32 {