various wit-dylib API tweaks (#2362)

* various `wit-dylib` API tweaks

I've recently ported `componentize-py` to use `wit-dylib` instead of its own
Wasm code generator and found it useful to tweak the `wit-dylib` APIs a bit.

The main idea here is to give `componentize-py` (and any similar build tool)
access to the metadata generated by `wit-dylib` _before_ the guest runs, as well
as match the types in that metadata up with the `wit_parser::TypeId`s from the
input world.  That allows the build tool to generate high-level binding code
ahead of time and later match it up with the metadata at runtime.

Specifically, this commit does the following:

- Add a `wit_dylib::create_with_metadata` function which returns both the generated module and the `Metadata` object produced for it.
- Add `id: TypeId` fields to all the "WIT type types" so that they can be matched up with the corresponding `wit-parser` types
- Add `index` methods to the `wit-dylib-ffi` wrapper types, allowing the interpreter to determine where the instance appears in its respective array
- Split the metadata `Function` type into separate `ImportFunction` and `ExportFunction` types, each with its own array in the `Wit` structure.  Imported and exported functions are used very differently by interpreters; separating them makes them easier to deal with.

Signed-off-by: Joel Dice <[email protected]>

* update tests to match `wit-dylib` changes

Signed-off-by: Joel Dice <[email protected]>

* address review feedback

Signed-off-by: Joel Dice <[email protected]>

* add `index` methods to remaining `wit-dylib-ffi` types

Signed-off-by: Joel Dice <[email protected]>

---------

Signed-off-by: Joel Dice <[email protected]>

Author: dicej

crates/wit-dylib/ffi/README.md

@@ -4,3 +4,20 @@ A sample Rust crate used to implement `wit_dylib.h` with a Rust trait with the
 possibility of an implementation being entirely safe Rust. Currently used in
 tests of the `wit-dylib` crate, but written in such a way that this could be
 used externally.
+
+## Regenerating `ffi.rs`
+
+If you've made changes to `wit_dylib.h` (or if someone else did, but forgot to
+update `ffi.rs`), you can use `rust-bindgen` to regenerate `ffi.rs`.
+
+First, install a recent version of `rust-bindgen` if you don't already have it:
+
+```
+cargo install bindgen-cli
+```
+
+Then, from the parent of this directory, run:
+
+```
+bindgen wit_dylib.h --allowlist-file wit_dylib.h --no-layout-tests --ignore-functions > ./ffi/src/ffi.rs
+```

crates/wit-dylib/ffi/src/ffi.rs

@@ -1,4 +1,4 @@
-/* automatically generated by rust-bindgen 0.69.4 */
+/* automatically generated by rust-bindgen 0.72.1 */
 
 pub const WIT_TYPE_U8: u32 = 0;
 pub const WIT_TYPE_U16: u32 = 1;
@@ -46,20 +46,30 @@ pub type wit_export_task_return_fn_t =
     ::std::option::Option<unsafe extern "C" fn(cx: *mut ::std::os::raw::c_void)>;
 #[repr(C)]
 #[derive(Debug, Copy, Clone)]
-pub struct wit_func {
+pub struct wit_import_func {
     pub interface: *const ::std::os::raw::c_char,
     pub name: *const ::std::os::raw::c_char,
     pub impl_: wit_import_fn_t,
     pub async_impl: wit_import_async_fn_t,
     pub async_lift_impl: wit_import_async_lift_fn_t,
-    pub task_return: wit_export_task_return_fn_t,
     pub nparams: usize,
     pub params: *const wit_type_t,
     pub result: wit_type_t,
     pub async_abi_area_size: usize,
     pub async_abi_area_align: usize,
 }
-pub type wit_func_t = wit_func;
+pub type wit_import_func_t = wit_import_func;
+#[repr(C)]
+#[derive(Debug, Copy, Clone)]
+pub struct wit_export_func {
+    pub interface: *const ::std::os::raw::c_char,
+    pub name: *const ::std::os::raw::c_char,
+    pub task_return: wit_export_task_return_fn_t,
+    pub nparams: usize,
+    pub params: *const wit_type_t,
+    pub result: wit_type_t,
+}
+pub type wit_export_func_t = wit_export_func;
 pub type wit_resource_drop_t = ::std::option::Option<unsafe extern "C" fn(arg1: u32)>;
 pub type wit_resource_new_t = ::std::option::Option<unsafe extern "C" fn(arg1: usize) -> u32>;
 pub type wit_resource_rep_t = ::std::option::Option<unsafe extern "C" fn(arg1: u32) -> usize>;
@@ -194,8 +204,10 @@ pub type wit_alias_t = wit_alias;
 #[derive(Debug, Copy, Clone)]
 pub struct wit {
     pub version: u32,
-    pub num_funcs: usize,
-    pub funcs: *const wit_func_t,
+    pub num_import_funcs: usize,
+    pub import_funcs: *const wit_import_func_t,
+    pub num_export_funcs: usize,
+    pub export_funcs: *const wit_export_func_t,
     pub num_resources: usize,
     pub resources: *const wit_resource_t,
     pub num_records: usize,

crates/wit-dylib/ffi/src/lib.rs

@@ -368,17 +368,17 @@ pub trait Interpreter: 'static {
         let _ = wit;
     }
 
-    fn export_start<'a>(wit: Wit, func: Function) -> Box<Self::CallCx<'a>>;
+    fn export_start<'a>(wit: Wit, func: ExportFunction) -> Box<Self::CallCx<'a>>;
 
-    fn export_call(wit: Wit, func: Function, cx: &mut Self::CallCx<'_>);
+    fn export_call(wit: Wit, func: ExportFunction, cx: &mut Self::CallCx<'_>);
 
     fn export_call_async(
         wit: Wit,
-        func: Function,
+        func: ExportFunction,
         cx: Box<Self::CallCx<'static>>,
     ) -> impl std::future::Future<Output = ()>;
 
-    fn export_finish(cx: Box<Self::CallCx<'_>>, func: Function) {
+    fn export_finish(cx: Box<Self::CallCx<'_>>, func: ExportFunction) {
         let _ = func;
         let _ = cx;
     }
@@ -503,7 +503,7 @@ pub trait RawInterpreter: Interpreter {
         debug_println!("export_start({which})");
         unsafe {
             let wit = Wit::from_raw(WIT_T);
-            let func = wit.func(which);
+            let func = wit.export_func(which);
             Box::into_raw(Self::export_start(wit, func)).cast()
         }
     }
@@ -512,7 +512,7 @@ pub trait RawInterpreter: Interpreter {
         debug_println!("export_call({cx:?}, {which})");
         unsafe {
             let wit = Wit::from_raw(WIT_T);
-            let func = wit.func(which);
+            let func = wit.export_func(which);
             Self::export_call(wit, func, Self::cx_mut(cx))
         }
     }
@@ -522,7 +522,7 @@ pub trait RawInterpreter: Interpreter {
         #[cfg(feature = "async")]
         unsafe {
             let wit = Wit::from_raw(WIT_T);
-            let func = wit.func(which);
+            let func = wit.export_func(which);
             wit_bindgen::rt::async_support::start_task(Self::export_call_async(
                 wit,
                 func,
@@ -550,7 +550,7 @@ pub trait RawInterpreter: Interpreter {
         debug_println!("export_finish({cx:?}, {which})");
         unsafe {
             let wit = Wit::from_raw(WIT_T);
-            let func = wit.func(which);
+            let func = wit.export_func(which);
             Self::export_finish(Box::from_raw(cx.cast()), func)
         }
     }