Add experiment to produce precompiled builds of serde_derive

precompiled/serde_derive/Cargo.toml

@@ -0,0 +1,17 @@
+[package]
+name = "serde_derive"
+version = "1.0.171"
+authors = ["David Tolnay <dtolnay@gmail.com>"]
+publish = false
+
+[lib]
+doctest = false
+
+[[bin]]
+name = "serde_derive"
+path = "main.rs"
+
+[dependencies]
+proc-macro2 = "1"
+quote = { version = "1", default-features = false }
+syn = { version = "2.0.25", default-features = false, features = ["clone-impls", "derive", "parsing", "printing"] }

precompiled/serde_derive/build.rs

@@ -0,0 +1,3 @@
+fn main() {
+    println!("cargo:rustc-cfg=precompiled");
+}

precompiled/serde_derive/main.rs

@@ -0,0 +1,22 @@
+extern crate proc_macro2;
+
+use proc_macro2::watt;
+use proc_macro2::watt::buffer::InputBuffer;
+use std::io::{self, Read, Write};
+
+fn main() {
+    let mut buf = Vec::new();
+    io::stdin().read_to_end(&mut buf).unwrap();
+
+    let mut buf = InputBuffer::new(&buf);
+    let derive = match buf.read_u8() {
+        0 => serde_derive::derive_serialize,
+        1 => serde_derive::derive_deserialize,
+        _ => unreachable!(),
+    };
+
+    let input = watt::load(&mut buf);
+    let output = derive(input);
+    let bytes = watt::linearize(output);
+    io::stdout().write_all(&bytes).unwrap();
+}

precompiled/serde_derive/src

@@ -0,0 +1 @@
+../../serde_derive/src