doc about exceptions

book/src/SUMMARY.md

@@ -20,6 +20,7 @@
     - [Arbitrary Rust types (opaque)](feature/lang_rust_opaque.md)
     - [Arbitrary Dart types (opaque)](feature/lang_dart_opaque.md)
     - [Type alias](feature/lang_type_alias.md)
+    - [Exceptions](feature/lang_exceptions.md)
   - [Zero copy](feature/zero_copy.md)
   - [Stream / Iterator](feature/stream.md)
   - [Async in Dart](feature/async_dart.md)

book/src/feature/lang_exceptions.md

@@ -0,0 +1,15 @@
+# Exceptions
+
+1. For Result/Error, the`anyhow::Result`/`anyhow::Error` is supported. It will be automatically converted to a Dart Exception.
+2. For `panic`s, it will also be automatically captured and converted to Dart exceptions.
+3. [#582](https://github.com/fzyzcjy/flutter_rust_bridge/pull/582) adds support for error hierarchy, or arbitrary error types. For example, you can create your own `CustomError` (such as using `thiserror`), and it will automatically be converted to a new Dart class. The PR is already almost completed (with the hard work done), and the missing piece is fixing the test errors. I have provided some guidance about how to fix it at the PR comments as well.
+
+## Example
+
+For example, the following code, when called by Dart code, will throw Dart exceptions.
+
+```rust,noplayground
+pub fn f() -> anyhow::Result<i32> { bail!("oops I failed") }
+
+pub fn g() -> i32 { panic!("oops I failed") }
+```

book/src/feature/lang_return_types.md

@@ -1,6 +1,6 @@
 # Return Types
 
-The return type can be either `anyhow::Result<YourType>`, or `YourType` directly.
+The return type can be either `anyhow::Result<YourType>`, or `YourType` directly. For exceptions (errors), please refer to [exceptions section](lang_exceptions.md) as well.
 
 ## Example