Auto merge of #119478 - bjorn3:no_serialize_specialization, r=wesleywiser

Avoid specialization in the metadata serialization code

With the exception of a perf-only specialization for byte slices and byte vectors.

This uses the same trick of introducing a new trait and having the Encodable and Decodable derives add a bound to it as used for TyEncoder/TyDecoder. The new code is clearer about which encoder/decoder uses which impl and it reduces the dependency of rustc on specialization, making it easier to remove support for specialization entirely or turn it into a construct that is only allowed for perf optimizations if we decide to do this.

2 files changed, 18 insertions, 0 deletions

diff --git a/compiler/rustc_macros/src/lib.rs b/compiler/rustc_macros/src/lib.rs
index f558b74be9a..f5d942b924e 100644
--- a/compiler/rustc_macros/src/lib.rs
+++ b/compiler/rustc_macros/src/lib.rs
@@ -56,6 +56,8 @@ decl_derive!(
     hash_stable::hash_stable_no_context_derive
 );
 
+decl_derive!([Decodable_Generic] => serialize::decodable_generic_derive);
+decl_derive!([Encodable_Generic] => serialize::encodable_generic_derive);
 decl_derive!([Decodable] => serialize::decodable_derive);
 decl_derive!([Encodable] => serialize::encodable_derive);
 decl_derive!([TyDecodable] => serialize::type_decodable_derive);
diff --git a/compiler/rustc_macros/src/serialize.rs b/compiler/rustc_macros/src/serialize.rs
index 047066ac681..9ca7ce09ba6 100644
--- a/compiler/rustc_macros/src/serialize.rs
+++ b/compiler/rustc_macros/src/serialize.rs
@@ -32,6 +32,14 @@ pub fn meta_decodable_derive(mut s: synstructure::Structure<'_>) -> proc_macro2:
 
 pub fn decodable_derive(mut s: synstructure::Structure<'_>) -> proc_macro2::TokenStream {
     let decoder_ty = quote! { __D };
+    s.add_impl_generic(parse_quote! {#decoder_ty: ::rustc_span::SpanDecoder});
+    s.add_bounds(synstructure::AddBounds::Generics);
+
+    decodable_body(s, decoder_ty)
+}
+
+pub fn decodable_generic_derive(mut s: synstructure::Structure<'_>) -> proc_macro2::TokenStream {
+    let decoder_ty = quote! { __D };
     s.add_impl_generic(parse_quote! {#decoder_ty: ::rustc_serialize::Decoder});
     s.add_bounds(synstructure::AddBounds::Generics);
 
@@ -130,6 +138,14 @@ pub fn meta_encodable_derive(mut s: synstructure::Structure<'_>) -> proc_macro2:
 
 pub fn encodable_derive(mut s: synstructure::Structure<'_>) -> proc_macro2::TokenStream {
     let encoder_ty = quote! { __E };
+    s.add_impl_generic(parse_quote! { #encoder_ty: ::rustc_span::SpanEncoder});
+    s.add_bounds(synstructure::AddBounds::Generics);
+
+    encodable_body(s, encoder_ty, false)
+}
+
+pub fn encodable_generic_derive(mut s: synstructure::Structure<'_>) -> proc_macro2::TokenStream {
+    let encoder_ty = quote! { __E };
     s.add_impl_generic(parse_quote! { #encoder_ty: ::rustc_serialize::Encoder});
     s.add_bounds(synstructure::AddBounds::Generics);