Simplify #[derive(Dupe)] generated code

Summary:
Put `assert_dupe` into crate rather than generating it for each type where `Dupe` is derived.

This should make compilation tiny bit faster.

Reviewed By: JakobDegen

Differential Revision: D56122611

fbshipit-source-id: ea97858d38d3af75114ca570e6cbad41d4c80467

gazebo/dupe/src/__macro_refs.rs

@@ -0,0 +1,15 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under both the MIT license found in the
+ * LICENSE-MIT file in the root directory of this source tree and the Apache
+ * License, Version 2.0 found in the LICENSE-APACHE file in the root directory
+ * of this source tree.
+ */
+
+#![doc(hidden)]
+
+use crate::Dupe;
+
+#[inline]
+pub const fn assert_dupe<T: Dupe + ?Sized>() {}

gazebo/dupe/src/lib.rs

@@ -9,6 +9,7 @@
 
 //! A cheap version of [`Clone`].
 
+pub mod __macro_refs;
 pub(crate) mod iter;
 pub(crate) mod option;
 

gazebo/dupe_derive/src/dupe.rs

@@ -7,15 +7,16 @@
  * of this source tree.
  */
 
+use proc_macro2::TokenStream;
 use quote::quote;
 use syn::parse_macro_input;
 use syn::parse_quote;
 use syn::DeriveInput;
 use syn::Ident;
+use syn::Type;
 use syn::TypeParamBound;
 
 use crate::util::add_trait_bounds;
-use crate::util::check_each_field_impls;
 use crate::util::extract_all_field_tys;
 
 pub fn derive_dupe(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
@@ -49,7 +50,7 @@ fn derive_dupe_explicit(
             return e.into_compile_error().into();
         }
     };
-    let check_each_field_dupe = check_each_field_impls(all_fields, parse_quote!(dupe::Dupe));
+    let check_each_field_dupe = check_each_field_dupe(all_fields);
 
     let check_func_name = Ident::new(
         &format!("__implicit_dupe_check_for_fields_of_{}", name),
@@ -69,3 +70,12 @@ fn derive_dupe_explicit(
 
     gen.into()
 }
+
+fn check_each_field_dupe<'a>(tys: impl IntoIterator<Item = &'a Type>) -> TokenStream {
+    let tys = tys.into_iter();
+    quote! {
+        #(
+            dupe::__macro_refs::assert_dupe::<#tys>();
+        )*
+    }
+}

gazebo/dupe_derive/src/util.rs

@@ -174,20 +174,3 @@ fn extract_all_field_tys_variant<'a>(data: &'a Variant) -> Box<dyn Iterator<Item
 fn extract_all_field_tys_enum<'a>(data: &'a DataEnum) -> Box<dyn Iterator<Item = &'a Type> + 'a> {
     Box::new(data.variants.iter().flat_map(extract_all_field_tys_variant))
 }
-
-pub(crate) fn check_each_field_impls<'a>(
-    iter: impl IntoIterator<Item = &'a Type>,
-    trait_required: Type,
-) -> TokenStream {
-    let checks = iter.into_iter().map(|ty| {
-        quote! {
-                assert_impl_all::<#ty>();
-        }
-    });
-
-    quote! {
-        fn assert_impl_all<T: ?Sized + #trait_required>() {}
-
-        #(#checks)*
-    }
-}