1 files changed, 55 insertions, 0 deletions
diff --git a/third_party/rust/derive_more-impl/src/deref.rs b/third_party/rust/derive_more-impl/src/deref.rs
new file mode 100644
index 0000000000..f87c64cc61
--- /dev/null
+++ b/third_party/rust/derive_more-impl/src/deref.rs
@@ -0,0 +1,55 @@
+use crate::utils::{add_extra_where_clauses, SingleFieldData, State};
+use proc_macro2::TokenStream;
+use quote::quote;
+use syn::{parse::Result, DeriveInput};
+
+/// Provides the hook to expand `#[derive(Deref)]` into an implementation of `Deref`
+pub fn expand(input: &DeriveInput, trait_name: &'static str) -> Result<TokenStream> {
+    let state = State::with_field_ignore_and_forward(
+        input,
+        trait_name,
+        trait_name.to_lowercase(),
+    )?;
+    let SingleFieldData {
+        input_type,
+        field_type,
+        trait_path,
+        casted_trait,
+        ty_generics,
+        member,
+        info,
+        ..
+    } = state.assert_single_enabled_field();
+
+    let (target, body, generics) = if info.forward {
+        (
+            quote! { #casted_trait::Target },
+            quote! { #casted_trait::deref(&#member) },
+            add_extra_where_clauses(
+                &input.generics,
+                quote! {
+                    where #field_type: #trait_path
+                },
+            ),
+        )
+    } else {
+        (
+            quote! { #field_type },
+            quote! { &#member },
+            input.generics.clone(),
+        )
+    };
+    let (impl_generics, _, where_clause) = generics.split_for_impl();
+
+    Ok(quote! {
+        #[automatically_derived]
+        impl #impl_generics #trait_path for #input_type #ty_generics #where_clause {
+            type Target = #target;
+
+            #[inline]
+            fn deref(&self) -> &Self::Target {
+                #body
+            }
+        }
+    })
+}