From f6ef35c5d323bef6fdc3d9fbd6048d4a350ef2cb Mon Sep 17 00:00:00 2001
From: Cameron McCormack <cam@mcc.id.au>
Date: Sat, 30 Mar 2019 00:16:08 +0000
Subject: [PATCH] style: Add support for deriving ToShmem.

Differential Revision: https://phabricator.services.mozilla.com/D17189
---
 components/style/Cargo.toml            |  1 +
 components/style/lib.rs                |  2 +
 components/to_shmem_derive/Cargo.toml  | 18 +++++++
 components/to_shmem_derive/lib.rs      | 26 +++++++++
 components/to_shmem_derive/to_shmem.rs | 74 ++++++++++++++++++++++++++
 5 files changed, 121 insertions(+)
 create mode 100644 components/to_shmem_derive/Cargo.toml
 create mode 100644 components/to_shmem_derive/lib.rs
 create mode 100644 components/to_shmem_derive/to_shmem.rs

diff --git a/components/style/Cargo.toml b/components/style/Cargo.toml
index c0dbc02a1863..005924cec21b 100644
--- a/components/style/Cargo.toml
+++ b/components/style/Cargo.toml
@@ -69,6 +69,7 @@ style_traits = {path = "../style_traits"}
 servo_url = {path = "../url", optional = true}
 thin-slice = "0.1.0"
 to_shmem = {path = "../to_shmem"}
+to_shmem_derive = {path = "../to_shmem_derive"}
 time = "0.1"
 uluru = "0.3"
 unicode-bidi = "0.3"
diff --git a/components/style/lib.rs b/components/style/lib.rs
index 294b8634d565..bd33dbeafe42 100644
--- a/components/style/lib.rs
+++ b/components/style/lib.rs
@@ -100,6 +100,8 @@ extern crate style_traits;
 extern crate thin_slice;
 extern crate time;
 extern crate to_shmem;
+#[macro_use]
+extern crate to_shmem_derive;
 extern crate uluru;
 extern crate unicode_bidi;
 #[allow(unused_extern_crates)]
diff --git a/components/to_shmem_derive/Cargo.toml b/components/to_shmem_derive/Cargo.toml
new file mode 100644
index 000000000000..e5aac7e0aafe
--- /dev/null
+++ b/components/to_shmem_derive/Cargo.toml
@@ -0,0 +1,18 @@
+[package]
+name = "to_shmem_derive"
+version = "0.0.1"
+authors = ["The Servo Project Developers"]
+license = "MPL-2.0"
+publish = false
+
+[lib]
+path = "lib.rs"
+proc-macro = true
+
+[dependencies]
+darling = "0.8"
+derive_common = { path = "../derive_common" }
+proc-macro2 = "0.4"
+quote = "0.6"
+syn = { version = "0.15", features = ["visit"] }
+synstructure = "0.10"
diff --git a/components/to_shmem_derive/lib.rs b/components/to_shmem_derive/lib.rs
new file mode 100644
index 000000000000..b820e7f85d03
--- /dev/null
+++ b/components/to_shmem_derive/lib.rs
@@ -0,0 +1,26 @@
+/* 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/. */
+
+#![recursion_limit = "128"]
+
+#[macro_use]
+extern crate darling;
+extern crate derive_common;
+extern crate proc_macro;
+extern crate proc_macro2;
+#[macro_use]
+extern crate quote;
+#[macro_use]
+extern crate syn;
+extern crate synstructure;
+
+use proc_macro::TokenStream;
+
+mod to_shmem;
+
+#[proc_macro_derive(ToShmem, attributes(shmem))]
+pub fn derive_to_shmem(stream: TokenStream) -> TokenStream {
+    let input = syn::parse(stream).unwrap();
+    to_shmem::derive(input).into()
+}
diff --git a/components/to_shmem_derive/to_shmem.rs b/components/to_shmem_derive/to_shmem.rs
new file mode 100644
index 000000000000..5021476aad46
--- /dev/null
+++ b/components/to_shmem_derive/to_shmem.rs
@@ -0,0 +1,74 @@
+/* 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 http://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;
+
+    let match_body = cg::fmap_match(&input, BindStyle::Ref, |binding| {
+        quote! {
+            ::std::mem::ManuallyDrop::into_inner(
+                ::to_shmem::ToShmem::to_shmem(#binding, builder)
+            )
+        }
+    });
+
+    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)]
+            fn to_shmem(
+                &self,
+                builder: &mut ::to_shmem::SharedMemoryBuilder,
+            ) -> ::std::mem::ManuallyDrop<Self> {
+                ::std::mem::ManuallyDrop::new(
+                    match *self {
+                        #match_body
+                    }
+                )
+            }
+        }
+    }
+}
+
+#[darling(attributes(shmem), default)]
+#[derive(Default, FromDeriveInput)]
+pub struct ShmemInputAttrs {
+    pub no_bounds: bool,
+}
+
+#[darling(attributes(shmem), default)]
+#[derive(Default, FromField)]
+pub struct ShmemFieldAttrs {
+    pub field_bound: bool,
+}