1 files changed, 44 insertions, 0 deletions
diff --git a/third_party/rust/derive_more-impl/src/deref_mut.rs b/third_party/rust/derive_more-impl/src/deref_mut.rs
new file mode 100644
index 0000000000..2d7a79db2a
--- /dev/null
+++ b/third_party/rust/derive_more-impl/src/deref_mut.rs
@@ -0,0 +1,44 @@
+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(DerefMut)]` into an implementation of `DerefMut`
+pub fn expand(input: &DeriveInput, trait_name: &'static str) -> Result<TokenStream> {
+    let state =
+        State::with_field_ignore_and_forward(input, trait_name, "deref_mut".into())?;
+    let SingleFieldData {
+        input_type,
+        trait_path,
+        casted_trait,
+        ty_generics,
+        field_type,
+        member,
+        info,
+        ..
+    } = state.assert_single_enabled_field();
+    let (body, generics) = if info.forward {
+        (
+            quote! { #casted_trait::deref_mut(&mut #member) },
+            add_extra_where_clauses(
+                &input.generics,
+                quote! {
+                    where #field_type: #trait_path
+                },
+            ),
+        )
+    } else {
+        (quote! { &mut #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 {
+            #[inline]
+            fn deref_mut(&mut self) -> &mut Self::Target {
+                #body
+            }
+        }
+    })
+}