diff --git a/gen/build/src/lib.rs b/gen/build/src/lib.rs
new file mode 100644
index 0000000..c1df580
--- /dev/null
+++ b/gen/build/src/lib.rs
@@ -0,0 +1,51 @@
+// Copyright 2020 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![forbid(unsafe_code)]
+
+use autocxx_engine::{BuilderContext, RebuildDependencyRecorder};
+use indexmap::set::IndexSet as HashSet;
+use std::{io::Write, sync::Mutex};
+
+pub type Builder = autocxx_engine::Builder<'static, CargoBuilderContext>;
+
+#[doc(hidden)]
+pub struct CargoBuilderContext;
+
+impl BuilderContext for CargoBuilderContext {
+    fn setup() {
+        env_logger::builder()
+            .format(|buf, record| writeln!(buf, "cargo:warning=MESSAGE:{}", record.args()))
+            .init();
+    }
+    fn get_dependency_recorder() -> Option<Box<dyn RebuildDependencyRecorder>> {
+        Some(Box::new(CargoRebuildDependencyRecorder::new()))
+    }
+}
+
+#[derive(Debug)]
+struct CargoRebuildDependencyRecorder {
+    printed_already: Mutex<HashSet<String>>,
+}
+
+impl CargoRebuildDependencyRecorder {
+    fn new() -> Self {
+        Self {
+            printed_already: Mutex::new(HashSet::new()),
+        }
+    }
+}
+
+impl RebuildDependencyRecorder for CargoRebuildDependencyRecorder {
+    fn record_header_file_dependency(&self, filename: &str) {
+        let mut already = self.printed_already.lock().unwrap();
+        if already.insert(filename.into()) {
+            println!("cargo:rerun-if-changed={}", filename);
+        }
+    }
+}