Merge pull request 132 from dtolnay/repr

Support round tripping anyhow::Error over C FFI as void*

src/lib.rs

@@ -361,6 +361,7 @@ pub use anyhow as format_err;
 ///     # Ok(())
 /// }
 /// ```
+#[repr(transparent)]
 pub struct Error {
     inner: ManuallyDrop<Box<ErrorImpl<()>>>,
 }

tests/test_ffi.rs

@@ -0,0 +1,18 @@
+#![deny(improper_ctypes, improper_ctypes_definitions)]
+
+use anyhow::anyhow;
+
+#[no_mangle]
+pub extern "C" fn anyhow1(err: anyhow::Error) {
+    println!("{:?}", err);
+}
+
+#[no_mangle]
+pub extern "C" fn anyhow2(err: &mut Option<anyhow::Error>) {
+    *err = Some(anyhow!("ffi error"));
+}
+
+#[no_mangle]
+pub extern "C" fn anyhow3() -> Option<anyhow::Error> {
+    Some(anyhow!("ffi error"))
+}