Doc fixes from review

CHANGELOG.md

@@ -15,7 +15,7 @@
 [All changes in [[UnreleasedVersion]]](https://github.com/mozilla/uniffi-rs/compare/v0.23.0...HEAD).
 
 ### ⚠️ Breaking Changes ⚠️
-- Implemented a new callback-interface ABI that signifacantly improves performance on Python and Kotlin.
+- ABI: Implemented a new callback-interface ABI that significantly improves performance on Python and Kotlin.  UniFFI users will automatically get the benefits of this without any code changes.  This is a breaking change because the new generated code is not compatible with code generated with UniFFI 0.23.x.
 
 ### What's changed
 

fixtures/benchmarks/src/benchmarks.udl

@@ -1,16 +1,16 @@
 namespace benchmarks {
-    // Run all benchmarks and print the results to stdout
-    void run_benchmarks(string language_name, TestCallbackInterface cb);
+  // Run all benchmarks and print the results to stdout
+  void run_benchmarks(string language_name, TestCallbackInterface cb);
 
-    // Test functions
+  // Test functions
   //
   // These are intented to test the overhead of Rust function calls including:
   // popping arguments from the stack, unpacking RustBuffers, pushing return
   // values back to the stack, etc.
 
-    string test_function(i32 a, i32 b, TestData data); // Should return data.bar
-    void test_void_return(i32 a, i32 b, TestData data);
-    void test_no_args_void_return();
+  string test_function(i32 a, i32 b, TestData data); // Should return data.bar
+  void test_void_return(i32 a, i32 b, TestData data);
+  void test_no_args_void_return();
 };
 
 dictionary TestData {

uniffi_core/src/ffi/foreigncallbacks.rs

@@ -128,8 +128,9 @@ use std::sync::atomic::{AtomicUsize, Ordering};
 /// * The `method` selector specifies the method that will be called on the object, by looking it up in a list of methods from
 ///   the IDL. The index is 1 indexed. Note that the list of methods is generated by at uniffi from the IDL and used in all
 ///   bindings: so we can rely on the method list being stable within the same run of uniffi.
-/// * `args_data` and `args_len` represents a serialized buffer of arguments to the function.
-///   UniFFI will deserialize it before passing individual arguments to the user's callback.
+/// * `args_data` and `args_len` represents a serialized buffer of arguments to the function. The scaffolding code
+///   writes the callback arguments to this buffer, in order, using `FfiConverter.write()`. The bindings code reads the
+///   arguments from the buffer and passes them to the user's callback.
 /// * `buf_ptr` is a pointer to where the resulting buffer will be written. UniFFI will allocate a
 ///   buffer to write the result into.
 /// * A callback returns: