Migration guide for 0.10

MIGRATION_GUIDE_0.10.md

@@ -0,0 +1,244 @@
+# Neon 0.10 Migration Guide
+
+With the API improvements of Neon 0.10, a few backwards-incompatible changes have been introduced. This migration guide provides all the information you should need to make the (small!) code changes required for upgrading to Neon 0.10.
+
+We have made an effort to minimize these changes, and believe they should typically lead to simpler, clearer code. **If you run into any trouble migrating your code to 0.10, please file an issue or reach out for help on the [community Slack](https://rust-bindings.slack.com/)!**
+
+# Major changes
+
+## Object property access is generic
+
+To improve the ergonomics of the common case of downcasting the result of property access to a specific type, the signature of `Object::get()` has been changed to have a generic return type. This means that code that follows `Object::get()` with `.downcast_or_throw()` or `.downcast::<V>().or_throw()` no longer needs to do so.
+
+**Before:**
+
+```rust
+obj.get(&mut cx, "name")?.downcast::<V, _>(&mut cx).or_throw(&mut cx)?
+```
+
+**After (option 1):**
+
+```rust
+obj.get::<V, _, _>(&mut cx, "name")?
+```
+
+**After (option 2):**
+
+```rust
+let v: Handle<V> = obj.get(&mut cx, "name")?
+```
+
+## Layered APIs for function calls
+
+The API for calling (or constructing, i.e. the Neon equivalent of the JavaScript `new` operator) a JS function has been split into two layered alternatives. The existing `.call()` and `.construct()` functions are now a lower-level primitive, which no longer offers automatic downcasting of arguments or result. But Neon 0.10 now offers a more convenient API for calling functions with an options object and method chaining, with the introduction of the `.call_with()` and `.construct_with()` methods.
+
+### Example: Calling a function
+
+**Before:**
+
+```rust
+let s: Handle<JsString> = ...;
+let n: Handle<JsNumber> = ...;
+let args: Vec<Handle<JsValue>> = vec![s.upcast(), n.upcast()];
+let this = cx.global();
+f.call(&mut cx, this, args)
+```
+
+**After (low-level API):**
+
+```rust
+let s: Handle<JsString> = cx.string("hello");
+let n: Handle<JsNumber> = cx.number(42);
+let this = cx.global();
+f.call(&mut cx, this, [s.upcast(), n.upcast()])
+```
+
+**After (high-level API):**
+
+```rust
+f.call_with(&cx)
+ .args((cx.string("hello"), cx.number(42)))
+ .apply(&mut cx)
+```
+
+### Example: Constructing with a function
+
+**Before:**
+
+```rust
+let s: Handle<JsString> = ...;
+let n: Handle<JsNumber> = ...;
+let args: Vec<Handle<JsValue>> = vec![s.upcast(), n.upcast()];
+f.construct(&mut cx, args)
+```
+
+**After (low-level API):**
+
+```rust
+let s: Handle<JsString> = ...;
+let n: Handle<JsNumber> = ...;
+f.construct(&mut cx, [s.upcast(), n.upcast()])
+```
+
+**After (high-level API):**
+
+```rust
+let s: Handle<JsString> = ...;
+let n: Handle<JsNumber> = ...;
+f.construct_with(&cx)
+ .args((s, n))
+ .apply(&mut cx)
+```
+
+## Idiomatic typed arrays
+
+Neon 0.10 replaces the previous typed array API with a more idiomatic API. JavaScript typed arrays (e.g. [`Uint32Array`](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Uint32Array)) can be represented with corresponding Rust types (e.g. [`JsTypedArray<u32>`](https://docs.rs/neon/0.10.0-alpha.3/neon/types/struct.JsTypedArray.html)), allowing easy access to their internals as Rust slices.
+
+### Example: Reading a buffer
+
+**Before:**
+
+```rust
+let b: Handle<JsArrayBuffer> = ...;
+{
+    let guard = cx.lock();
+    let data = b.borrow(&guard);
+    let slice = data.as_slice::<u32>();
+    ...
+}
+```
+
+**After:**
+
+```rust
+let b: Handle<JsTypedArray<u32>> = ...;
+let slice = b.as_slice(&cx);
+```
+
+### Example: Reading and writing buffers
+
+**Before:**
+
+```rust
+let b1: Handle<JsArrayBuffer> = ...;
+let b2: Handle<JsArrayBuffer> = ...;
+{
+    let guard = cx.lock();
+    let data1 = b1.borrow(&guard);
+    let data2 = b2.borrow(&guard);
+    let slice1 = data1.as_slice::<u32>();
+    let slice2 = data2.as_slice::<u32>();
+    ...
+}
+```
+
+**After:**
+
+```rust
+let src_buf: Handle<JsTypedArray<u32>> = ...;
+let dst_buf: Handle<JsTypedArray<u32>> = ...;
+{
+    let lock = cx.lock();
+    let src = src_buf.as_slice(&lock).unwrap();
+    let dst = dst_buf.as_mut_slice(&lock).unwrap();
+    ...
+}
+```
+
+### Example: Casting buffer types
+
+Previous versions of Neon came with a special datatype for casting the data of an ArrayBuffer, but this had incomplete handling of unaligned data and is deprecated in Neon 0.10. Crates like [bytemuck](https://crates.io/crates/bytemuck) can be used for casting buffer slices.
+
+**Before:**
+
+```rust
+let b: Handle<JsArrayBuffer> = ...;
+{
+    let guard = cx.lock();
+    let data = b.borrow(&guard);
+    let u8_slice = data.as_slice::<u8>();
+    let f32_slice = data.as_slice::<f32>();
+    ...
+}
+```
+
+**After:**
+
+```rust
+use bytemuck::cast_slice;
+
+let b: Handle<JsArrayBuffer> = ...;
+let u8_slice = b.as_slice(&cx);
+let f32_slice: &[f32] = cast_slice(u8_slice);
+```
+
+# Minor changes
+
+## Uncaught errors in tasks
+
+Starting with 0.10, uncaught errors (whether Rust panics or JavaScript exceptions) in a task are now captured and reported to Node as an [`unhandledRejection ` event](https://nodejs.org/api/process.html#event-unhandledrejection). Previously, an uncaught JavaScript exception would be ignored. To handle uncaught exceptions, either wrap the body of a task with [`try_catch`](https://docs.rs/neon/0.10.0-alpha.3/neon/context/trait.Context.html#method.try_catch) or, alternatively, capture all uncaught rejections in Node with `process.on("unhandledRejection, (err) => {})`.
+
+**Before:**
+
+```rust
+cx.task(|| "hello".to_string())
+  .and_then(|mut cx, _| {
+      cx.throw_error("ignore me")
+  })
+```
+
+**After:**
+
+```rust
+cx.task(|| "hello".to_string())
+  .and_then(|mut cx, _| {
+      let _ = cx.try_catch(() {
+          cx.throw_error("ignore me")
+      });
+      Ok(())
+  })
+```
+
+## `Channel::send` returns `JoinHandle`
+
+The [`Channel::send()`](https://docs.rs/neon/0.10.0-alpha.3/neon/event/struct.Channel.html#method.send) method now returns a [`JoinHandle`](https://docs.rs/neon/0.10.0-alpha.3/neon/event/struct.JoinHandle.html) type instead of `()`, allowing code to optionally and conveniently block on the result with [`JoinHandle::join()`](https://docs.rs/neon/0.10.0-alpha.3/neon/event/struct.JoinHandle.html#method.join). Non-blocking code should usually work with little to no change; sometimes a semicolon may be needed to explicitly ignore the `JoinHandle`.
+
+**Before:**
+
+```rust
+fn helper<'a, C: Context<'a>>(cx: &mut C, ch: Channel) {
+    ch.send(...)
+}
+```
+
+**After:**
+
+```rust
+fn helper<'a, C: Context<'a>>(cx: &mut C, ch: Channel) {
+    ch.send(...);
+}
+```
+
+## Value types aren't cloneable
+
+Previous versions of Neon had a safety bug in allowing types that implement the [`Value`](https://docs.rs/neon/0.10.0-alpha.3/neon/types/trait.Value.html) trait to be cloned. This has been fixed in Neon 0.10. It should be rare for code to ever need to clone a value. In most cases where this may be occurring, a [`Handle`](https://docs.rs/neon/0.10.0-alpha.3/neon/handle/struct.Handle.html) or reference (`&`) should work. For longer-lived use cases such as storing a value in a Rust static variable, use a [`Root`](https://docs.rs/neon/0.10.0-alpha.3/neon/handle/struct.Root.html).
+
+**Before:**
+
+```rust
+fn helper<'a, C: Context<'a>>(cx: &mut C, s: JsString) -> ... {
+    ...
+}
+```
+
+**After:**
+
+```rust
+fn helper<'a, C: Context<'a>>(cx: &mut C, s: Handle<JsString>) -> ... {
+    ...
+}
+```
+
+## Context methods now all take `&mut self`
+
+Context methods such as [`execute_scoped`](https://docs.rs/neon/0.10.0-alpha.3/neon/context/trait.Context.html#method.execute_scoped), [`compute_scoped`](https://docs.rs/neon/0.10.0-alpha.3/neon/context/trait.Context.html#method.compute_scoped), and [`lock`](https://docs.rs/neon/0.10.0-alpha.3/neon/context/trait.Context.html#method.lock) all take `&mut self` instead of the previous `&self`. This was necessary for safety and is more consistent with other `Context` methods. In normal usage, this should not require code changes.

README.md

@@ -27,13 +27,11 @@ _**Note:** This will create a new project with the `napi-backend` and some docum
 See our [Neon fundamentals docs](https://neon-bindings.com/docs/intro) and
 our [API docs](https://docs.rs/neon/latest/neon).
 
-## Node-API (formerly N-API) Migration Guide
+## Neon 0.10 Migration Guide
 
-We've ported Neon to a new backend based on [Node-API (formerly N-API)](https://nodejs.org/api/n-api.html), which will
-be the basis for Neon 1.0.
+The latest version of Neon, 0.10, includes a few small breaking changes in order to clean up and improve the usability of our APIs.
 
-**Read the new [migration guide](https://github.com/neon-bindings/neon/blob/main/MIGRATION_GUIDE.md)** to learn how to
-port your Neon projects to N-API!
+**Read the new [migration guide](https://github.com/neon-bindings/neon/blob/main/MIGRATION_GUIDE_0.10.md)** to learn how to port your Neon projects to 0.10!
 
 ## Platform Support