1 files changed, 78 insertions, 0 deletions
diff --git a/servo/components/to_shmem_derive/to_shmem.rs b/servo/components/to_shmem_derive/to_shmem.rs
new file mode 100644
index 0000000000..157730c5a5
--- /dev/null
+++ b/servo/components/to_shmem_derive/to_shmem.rs
@@ -0,0 +1,78 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+use derive_common::cg;
+use proc_macro2::TokenStream;
+use syn;
+use synstructure::{BindStyle, Structure};
+
+pub fn derive(mut input: syn::DeriveInput) -> TokenStream {
+    let mut where_clause = input.generics.where_clause.take();
+    let attrs = cg::parse_input_attrs::<ShmemInputAttrs>(&input);
+    if !attrs.no_bounds {
+        for param in input.generics.type_params() {
+            cg::add_predicate(&mut where_clause, parse_quote!(#param: ::to_shmem::ToShmem));
+        }
+    }
+    for variant in Structure::new(&input).variants() {
+        for binding in variant.bindings() {
+            let attrs = cg::parse_field_attrs::<ShmemFieldAttrs>(&binding.ast());
+            if attrs.field_bound {
+                let ty = &binding.ast().ty;
+                cg::add_predicate(&mut where_clause, parse_quote!(#ty: ::to_shmem::ToShmem))
+            }
+        }
+    }
+
+    input.generics.where_clause = where_clause;
+
+    // Do all of the `to_shmem()?` calls before the `ManuallyDrop::into_inner()`
+    // calls, so that we don't drop a value in the shared memory buffer if one
+    // of the `to_shmem`s fails.
+    let match_body = cg::fmap2_match(
+        &input,
+        BindStyle::Ref,
+        |binding| {
+            quote! {
+                ::to_shmem::ToShmem::to_shmem(#binding, builder)?
+            }
+        },
+        |binding| {
+            Some(quote! {
+                ::std::mem::ManuallyDrop::into_inner(#binding)
+            })
+        },
+    );
+
+    let name = &input.ident;
+    let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
+
+    quote! {
+        impl #impl_generics ::to_shmem::ToShmem for #name #ty_generics #where_clause {
+            #[allow(unused_variables, unreachable_code)]
+            fn to_shmem(
+                &self,
+                builder: &mut ::to_shmem::SharedMemoryBuilder,
+            ) -> ::to_shmem::Result<Self> {
+                Ok(::std::mem::ManuallyDrop::new(
+                    match *self {
+                        #match_body
+                    }
+                ))
+            }
+        }
+    }
+}
+
+#[derive(Default, FromDeriveInput)]
+#[darling(attributes(shmem), default)]
+pub struct ShmemInputAttrs {
+    pub no_bounds: bool,
+}
+
+#[derive(Default, FromField)]
+#[darling(attributes(shmem), default)]
+pub struct ShmemFieldAttrs {
+    pub field_bound: bool,
+}