1 files changed, 62 insertions, 0 deletions
diff --git a/third_party/rust/uniffi_build/src/lib.rs b/third_party/rust/uniffi_build/src/lib.rs
new file mode 100644
index 0000000000..2532b4be67
--- /dev/null
+++ b/third_party/rust/uniffi_build/src/lib.rs
@@ -0,0 +1,62 @@
+/* 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 anyhow::{Context, Result};
+use camino::Utf8Path;
+use std::env;
+
+/// Generate the rust "scaffolding" required to build a uniffi component.
+///
+/// Given the path to an UDL file, this function will call the `uniffi-bindgen`
+/// command-line tool to generate the `pub extern "C"` functions and other supporting
+/// code required to expose the defined interface from Rust. The expectation is that
+/// this will be called from a crate's build script, and the resulting file will
+/// be `include!()`ed into the build.
+///
+/// Given an UDL file named `example.udl`, the generated scaffolding will be written
+/// into a file named `example.uniffi.rs` in the `$OUT_DIR` directory.
+///
+/// If the "builtin-bindgen" feature is enabled then this will take a dependency on
+/// the `uniffi_bindgen` crate and call its methods directly, rather than using the
+/// command-line tool. This is mostly useful for developers who are working on uniffi
+/// itself and need to test out their changes to the bindings generator.
+pub fn generate_scaffolding(udl_file: impl AsRef<Utf8Path>) -> Result<()> {
+    let udl_file = udl_file.as_ref();
+
+    println!("cargo:rerun-if-changed={udl_file}");
+    // The UNIFFI_TESTS_DISABLE_EXTENSIONS variable disables some bindings, but it is evaluated
+    // at *build* time, so we need to rebuild when it changes.
+    println!("cargo:rerun-if-env-changed=UNIFFI_TESTS_DISABLE_EXTENSIONS");
+    // Why don't we just depend on uniffi-bindgen and call the public functions?
+    // Calling the command line helps making sure that the generated swift/Kotlin/whatever
+    // bindings were generated with the same version of uniffi as the Rust scaffolding code.
+    let out_dir = env::var("OUT_DIR").context("$OUT_DIR missing?!")?;
+    run_uniffi_bindgen_scaffolding(out_dir.as_ref(), udl_file)
+}
+
+#[cfg(not(feature = "builtin-bindgen"))]
+fn run_uniffi_bindgen_scaffolding(out_dir: &Utf8Path, udl_file: &Utf8Path) -> Result<()> {
+    use anyhow::bail;
+    use std::process::Command;
+
+    let status = Command::new("uniffi-bindgen")
+        .arg("scaffolding")
+        .arg("--out-dir")
+        .arg(out_dir)
+        .arg(udl_file)
+        .status()
+        .context(
+            "failed to run `uniffi-bindgen` - \
+             have you installed it via `cargo install uniffi_bindgen`?",
+        )?;
+    if !status.success() {
+        bail!("Error while generating scaffolding code");
+    }
+    Ok(())
+}
+
+#[cfg(feature = "builtin-bindgen")]
+fn run_uniffi_bindgen_scaffolding(out_dir: &Utf8Path, udl_file: &Utf8Path) -> Result<()> {
+    uniffi_bindgen::generate_component_scaffolding(udl_file, None, Some(out_dir), false)
+}