Remove build script from serde_derive

The current serde_derive's MSRV is 1.56, and both underscore consts and
ptr::addr_of! are always available.

serde_derive/src/de.rs

@@ -69,8 +69,6 @@ pub fn expand_derive_deserialize(
 
     Ok(dummy::wrap_in_const(
         cont.attrs.custom_serde_path(),
-        "DESERIALIZE",
-        ident,
         impl_block,
     ))
 }

serde_derive/src/dummy.rs

@@ -1,23 +1,11 @@
-use proc_macro2::{Ident, TokenStream};
-use quote::format_ident;
+use proc_macro2::TokenStream;
 
 use syn;
 use try;
 
-pub fn wrap_in_const(
-    serde_path: Option<&syn::Path>,
-    trait_: &str,
-    ty: &Ident,
-    code: TokenStream,
-) -> TokenStream {
+pub fn wrap_in_const(serde_path: Option<&syn::Path>, code: TokenStream) -> TokenStream {
     let try_replacement = try::replacement();
 
-    let dummy_const = if cfg!(no_underscore_consts) {
-        format_ident!("_IMPL_{}_FOR_{}", trait_, unraw(ty))
-    } else {
-        format_ident!("_")
-    };
-
     let use_serde = match serde_path {
         Some(path) => quote! {
             use #path as _serde;
@@ -31,14 +19,10 @@ pub fn wrap_in_const(
     quote! {
         #[doc(hidden)]
         #[allow(non_upper_case_globals, unused_attributes, unused_qualifications)]
-        const #dummy_const: () = {
+        const _: () = {
             #use_serde
             #try_replacement
             #code
         };
     }
 }
-
-fn unraw(ident: &Ident) -> String {
-    ident.to_string().trim_start_matches("r#").to_owned()
-}

serde_derive/src/pretend.rs

@@ -97,29 +97,14 @@ fn pretend_fields_used_struct_packed(cont: &Container, fields: &[Field]) -> Toke
 
     let members = fields.iter().map(|field| &field.member).collect::<Vec<_>>();
 
-    #[cfg(not(no_ptr_addr_of))]
-    {
-        quote! {
-            match _serde::__private::None::<&#type_ident #ty_generics> {
-                _serde::__private::Some(__v @ #type_ident { #(#members: _),* }) => {
-                    #(
-                        let _ = _serde::__private::ptr::addr_of!(__v.#members);
-                    )*
-                }
-                _ => {}
-            }
-        }
-    }
-
-    #[cfg(no_ptr_addr_of)]
-    {
-        let placeholders = (0usize..).map(|i| format_ident!("__v{}", i));
-
-        quote! {
-            match _serde::__private::None::<#type_ident #ty_generics> {
-                _serde::__private::Some(#type_ident { #(#members: #placeholders),* }) => {}
-                _ => {}
+    quote! {
+        match _serde::__private::None::<&#type_ident #ty_generics> {
+            _serde::__private::Some(__v @ #type_ident { #(#members: _),* }) => {
+                #(
+                    let _ = _serde::__private::ptr::addr_of!(__v.#members);
+                )*
             }
+            _ => {}
         }
     }
 }

serde_derive/src/ser.rs

@@ -59,8 +59,6 @@ pub fn expand_derive_serialize(
 
     Ok(dummy::wrap_in_const(
         cont.attrs.custom_serde_path(),
-        "SERIALIZE",
-        ident,
         impl_block,
     ))
 }