wasmtime/runtime/component/

func.rs

use crate::component::instance::Instance;
use crate::component::matching::InstanceType;
use crate::component::storage::storage_as_slice;
use crate::component::types::ComponentFunc;
use crate::component::values::Val;
use crate::prelude::*;
use crate::runtime::vm::component::{ComponentInstance, InstanceFlags};
use crate::runtime::vm::{Export, SendSyncPtr, UncaughtException, VMFuncRef};
use crate::store::StoreOpaque;
use crate::{AsContext, AsContextMut, StoreContextMut, ValRaw};
use core::mem::{self, MaybeUninit};
use core::ptr::NonNull;
use wasmtime_environ::component::{
    CanonicalOptions, ExportIndex, InterfaceType, MAX_FLAT_PARAMS, MAX_FLAT_RESULTS, OptionsIndex,
    TypeFuncIndex, TypeTuple,
};

mod host;
mod options;
mod typed;
pub use self::host::*;
pub use self::options::*;
pub use self::typed::*;

/// A WebAssembly component function which can be called.
///
/// This type is the dual of [`wasmtime::Func`](crate::Func) for component
/// functions. An instance of [`Func`] represents a component function from a
/// component [`Instance`](crate::component::Instance). Like with
/// [`wasmtime::Func`](crate::Func) it's possible to call functions either
/// synchronously or asynchronously and either typed or untyped.
#[derive(Copy, Clone, Debug)]
#[repr(C)] // here for the C API.
pub struct Func {
    instance: Instance,

    /// The export index of this lifted function within its component.
    index: ExportIndex,

    /// The resolved core `VMFuncRef` for this lifted function, whose lifetime
    /// is bound to the `Store` this `Func` belongs to.
    ///
    /// Note that this field has an `unsafe_*` prefix to discourage use of it.
    /// This is only safe to read/use if the store that owns `instance`
    /// (identified by `instance.id().store_id()`) is in scope. Use the
    /// `self.lifted_core_func()` method instead of this field to perform this
    /// check.
    unsafe_func_ref: SendSyncPtr<VMFuncRef>,
}

// Double-check that the C representation in `component/func.h` matches our
// in-Rust representation here in terms of size/alignment/etc.
const _: () = {
    #[repr(C)]
    struct T(u64, u32);
    #[repr(C)]
    struct C(T, u32, *mut u8);
    assert!(core::mem::size_of::<C>() == core::mem::size_of::<Func>());
    assert!(core::mem::align_of::<C>() == core::mem::align_of::<Func>());
    assert!(core::mem::offset_of!(Func, instance) == 0);
};

impl Func {
    pub(crate) fn from_lifted_func(
        store: &mut StoreOpaque,
        instance: Instance,
        index: ExportIndex,
    ) -> Func {
        let (component, store) = instance.component_and_store_mut(store);
        let (_ty, def, _options) = component.export_lifted_function(index);
        let unsafe_func_ref = match instance.lookup_vmdef(store, def) {
            Export::Function(f) => f.vm_func_ref(store),
            _ => unreachable!(),
        }
        .into();

        Func {
            instance,
            index,
            unsafe_func_ref,
        }
    }

    /// Attempt to cast this [`Func`] to a statically typed [`TypedFunc`] with
    /// the provided `Params` and `Return`.
    ///
    /// This function will perform a type-check at runtime that the [`Func`]
    /// takes `Params` as parameters and returns `Return`. If the type-check
    /// passes then a [`TypedFunc`] will be returned which can be used to
    /// invoke the function in an efficient, statically-typed, and ergonomic
    /// manner.
    ///
    /// The `Params` type parameter here is a tuple of the parameters to the
    /// function. A function which takes no arguments should use `()`, a
    /// function with one argument should use `(T,)`, etc. Note that all
    /// `Params` must also implement the [`Lower`] trait since they're going
    /// into wasm.
    ///
    /// The `Return` type parameter is the return value of this function. A
    /// return value of `()` means that there's no return (similar to a Rust
    /// unit return) and otherwise a type `T` can be specified. Note that the
    /// `Return` must also implement the [`Lift`] trait since it's coming from
    /// wasm.
    ///
    /// Types specified here must implement the [`ComponentType`] trait. This
    /// trait is implemented for built-in types to Rust such as integer
    /// primitives, floats, `Option<T>`, `Result<T, E>`, strings, `Vec<T>`, and
    /// more. As parameters you'll be passing native Rust types.
    ///
    /// See the documentation for [`ComponentType`] for more information about
    /// supported types.
    ///
    /// # Errors
    ///
    /// If the function does not actually take `Params` as its parameters or
    /// return `Return` then an error will be returned.
    ///
    /// This function will return an [`OutOfMemory`][crate::OutOfMemory] error when
    /// memory allocation fails. See the `OutOfMemory` type's documentation for
    /// details on Wasmtime's out-of-memory handling.
    ///
    /// # Panics
    ///
    /// This function will panic if `self` is not owned by the `store`
    /// specified.
    ///
    /// # Examples
    ///
    /// Calling a function which takes no parameters and has no return value:
    ///
    /// ```
    /// # use wasmtime::component::Func;
    /// # use wasmtime::Store;
    /// # fn foo(func: &Func, store: &mut Store<()>) -> wasmtime::Result<()> {
    /// let typed = func.typed::<(), ()>(&store)?;
    /// typed.call(store, ())?;
    /// # Ok(())
    /// # }
    /// ```
    ///
    /// Calling a function which takes one string parameter and returns a
    /// string:
    ///
    /// ```
    /// # use wasmtime::component::Func;
    /// # use wasmtime::Store;
    /// # fn foo(func: &Func, mut store: Store<()>) -> wasmtime::Result<()> {
    /// let typed = func.typed::<(&str,), (String,)>(&store)?;
    /// let ret = typed.call(&mut store, ("Hello, ",))?.0;
    /// println!("returned string was: {}", ret);
    /// # Ok(())
    /// # }
    /// ```
    ///
    /// Calling a function which takes multiple parameters and returns a boolean:
    ///
    /// ```
    /// # use wasmtime::component::Func;
    /// # use wasmtime::Store;
    /// # fn foo(func: &Func, mut store: Store<()>) -> wasmtime::Result<()> {
    /// let typed = func.typed::<(u32, Option<&str>, &[u8]), (bool,)>(&store)?;
    /// let ok: bool = typed.call(&mut store, (1, Some("hello"), b"bytes!"))?.0;
    /// println!("return value was: {ok}");
    /// # Ok(())
    /// # }
    /// ```
    pub fn typed<Params, Return>(&self, store: impl AsContext) -> Result<TypedFunc<Params, Return>>
    where
        Params: ComponentNamedList + Lower,
        Return: ComponentNamedList + Lift,
    {
        self._typed(store.as_context().0, None)
    }

    pub(crate) fn _typed<Params, Return>(
        &self,
        store: &StoreOpaque,
        instance: Option<&ComponentInstance>,
    ) -> Result<TypedFunc<Params, Return>>
    where
        Params: ComponentNamedList + Lower,
        Return: ComponentNamedList + Lift,
    {
        self.typecheck::<Params, Return>(store, instance)?;
        unsafe { Ok(TypedFunc::new_unchecked(*self)) }
    }

    fn typecheck<Params, Return>(
        &self,
        store: &StoreOpaque,
        instance: Option<&ComponentInstance>,
    ) -> Result<()>
    where
        Params: ComponentNamedList + Lower,
        Return: ComponentNamedList + Lift,
    {
        let cx = InstanceType::new(instance.unwrap_or_else(|| self.instance.id().get(store)));
        let ty = &cx.types[self.ty_index(store)];

        Params::typecheck(&InterfaceType::Tuple(ty.params), &cx)
            .context("type mismatch with parameters")?;
        Return::typecheck(&InterfaceType::Tuple(ty.results), &cx)
            .context("type mismatch with results")?;

        Ok(())
    }

    /// Get the type of this function.
    pub fn ty(&self, store: impl AsContext) -> ComponentFunc {
        let store = store.as_context().0;
        let cx = InstanceType::new(self.instance.id().get(store));
        let ty = self.ty_index(store);
        ComponentFunc::from(ty, &cx)
    }

    fn ty_index(&self, store: &StoreOpaque) -> TypeFuncIndex {
        let instance = self.instance.id().get(store);
        let (ty, _, _) = instance.component().export_lifted_function(self.index);
        ty
    }

    /// Invokes this function with the `params` given and returns the result.
    ///
    /// The `params` provided must match the parameters that this function takes
    /// in terms of their types and the number of parameters. Results will be
    /// written to the `results` slice provided if the call completes
    /// successfully. The initial types of the values in `results` are ignored
    /// and values are overwritten to write the result. It's required that the
    /// size of `results` exactly matches the number of results that this
    /// function produces.
    ///
    /// This will also call the corresponding `post-return` function, if any.
    ///
    /// For more detailed information see the documentation of
    /// [`TypedFunc::call`].
    ///
    /// # Errors
    ///
    /// Returns an error in situations including but not limited to:
    ///
    /// * `params` is not the right size or if the values have the wrong type
    /// * `results` is not the right size
    /// * A trap occurs while executing the function
    /// * The function calls a host function which returns an error
    /// * The `store` used requires the use of [`Func::call_async`] instead. See
    ///   [store documentation](crate#async) for more information.
    /// * The call is recursive from within e.g. a `call_async` invocation.
    /// * If the function is async-typed or async-lifted, in which case either
    ///   [`Self::call_async`] or [`Self::call_concurrent`] must be used.
    ///
    /// See [`TypedFunc::call`] for more information in addition to
    /// [`wasmtime::Func::call`](crate::Func::call).
    ///
    /// This function will return an [`OutOfMemory`][crate::OutOfMemory] error when
    /// memory allocation fails. See the `OutOfMemory` type's documentation for
    /// details on Wasmtime's out-of-memory handling.
    ///
    /// # Panics
    ///
    /// Panics if `store` does not own this function.
    pub fn call(
        &self,
        mut store: impl AsContextMut,
        params: &[Val],
        results: &mut [Val],
    ) -> Result<()> {
        let mut store = store.as_context_mut();
        store.0.validate_sync_call()?;
        self.call_impl(store.as_context_mut(), params, results)?;
        Ok(())
    }

    /// Exactly like [`Self::call`] except for use on async stores.
    ///
    /// # Errors
    ///
    /// This function will return an [`OutOfMemory`][crate::OutOfMemory] error when
    /// memory allocation fails. See the `OutOfMemory` type's documentation for
    /// details on Wasmtime's out-of-memory handling.
    ///
    /// # Panics
    ///
    /// Panics if `store` does not own this function.
    #[cfg(feature = "async")]
    pub async fn call_async(
        &self,
        mut store: impl AsContextMut<Data: Send>,
        params: &[Val],
        results: &mut [Val],
    ) -> Result<()> {
        let mut store = store.as_context_mut();

        #[cfg(feature = "component-model-async")]
        if store.0.concurrency_support() {
            return store
                .run_concurrent_trap_on_idle(async |store| {
                    self.call_concurrent(store, params, results).await
                })
                .await?;
        }

        store
            .on_fiber(|store| self.call_impl(store, params, results))
            .await?
    }

    pub(crate) fn check_params_results<T>(
        &self,
        store: StoreContextMut<T>,
        params: &[Val],
        results: &mut [Val],
    ) -> Result<()> {
        let ty = self.ty(&store);
        if ty.params().len() != params.len() {
            bail!(
                "expected {} argument(s), got {}",
                ty.params().len(),
                params.len(),
            );
        }

        if ty.results().len() != results.len() {
            bail!(
                "expected {} result(s), got {}",
                ty.results().len(),
                results.len(),
            );
        }

        Ok(())
    }

    fn call_impl(
        &self,
        mut store: impl AsContextMut,
        params: &[Val],
        results: &mut [Val],
    ) -> Result<()> {
        let mut store = store.as_context_mut();

        self.check_params_results(store.as_context_mut(), params, results)?;

        if self.is_async(store.0) {
            bail!(
                "cannot synchronously call an async function; \
                 use `call_async` or `call_concurrent` instead"
            );
        }

        // SAFETY: the chosen representations of type parameters to `call_raw`
        // here should be generally safe to work with:
        //
        // * parameters use `MaybeUninit<[MaybeUninit<ValRaw>; MAX_FLAT_PARAMS]>`
        //   which represents the maximal possible number of parameters that can
        //   be passed to lifted component functions. This is modeled with
        //   `MaybeUninit` to represent how it all starts as uninitialized and
        //   thus can't be safely read during lowering.
        //
        // * results are modeled as `[ValRaw; MAX_FLAT_RESULTS]` which
        //   represents the maximal size of values that can be returned. Note
        //   that if the function doesn't actually have a return value then the
        //   `ValRaw` inside the array will have undefined contents. That is
        //   safe in Rust, however, due to `ValRaw` being a `union`. The
        //   contents should dynamically not be read due to the type of the
        //   function used here matching the actual lift.
        let result = unsafe {
            self.call_raw(
                store.as_context_mut(),
                |cx, ty, dst: &mut MaybeUninit<[MaybeUninit<ValRaw>; MAX_FLAT_PARAMS]>| {
                    // SAFETY: it's safe to assume that
                    // `MaybeUninit<array-of-maybe-uninit>` is initialized because
                    // each individual element is still considered uninitialized.
                    let dst: &mut [MaybeUninit<ValRaw>] = dst.assume_init_mut();
                    Self::lower_args(cx, params, ty, dst)
                },
                |cx, results_ty, src: &[ValRaw; MAX_FLAT_RESULTS]| {
                    let max_flat = MAX_FLAT_RESULTS;
                    for (result, slot) in
                        Self::lift_results(cx, results_ty, src, max_flat)?.zip(results)
                    {
                        *slot = result?;
                    }
                    Ok(())
                },
            )
        };

        if result.is_err() {
            store.0.set_trapped();
        }

        result
    }

    #[inline]
    pub(crate) fn lifted_core_func(&self, store: &StoreOpaque) -> NonNull<VMFuncRef> {
        self.instance.id().assert_belongs_to(store.id());
        self.unsafe_func_ref.as_non_null()
    }

    /// Returns whether this function is async-typed or async-lifted, either of
    /// which means it can't be called synchronously.
    pub(crate) fn is_async(&self, store: &StoreOpaque) -> bool {
        let instance = self.instance.id().get(store);
        let component = instance.component();
        let (ty, _def, options) = component.export_lifted_function(self.index);
        component.types()[ty].async_ || component.env_component().options[options].async_
    }

    pub(crate) fn abi_info<'a>(
        &self,
        store: &'a StoreOpaque,
    ) -> (
        OptionsIndex,
        InstanceFlags,
        TypeFuncIndex,
        &'a CanonicalOptions,
    ) {
        let vminstance = self.instance.id().get(store);
        let component = vminstance.component();
        let (ty, _def, options_index) = component.export_lifted_function(self.index);
        let raw_options = &component.env_component().options[options_index];
        (
            options_index,
            vminstance.instance_flags(raw_options.instance),
            ty,
            raw_options,
        )
    }

    /// Invokes the underlying wasm function, lowering arguments and lifting the
    /// result.
    ///
    /// The `lower` function and `lift` function provided here are what actually
    /// do the lowering and lifting. The `LowerParams` and `LowerReturn` types
    /// are what will be allocated on the stack for this function call. They
    /// should be appropriately sized for the lowering/lifting operation
    /// happening.
    ///
    /// # Safety
    ///
    /// The safety of this function relies on the correct definitions of the
    /// `LowerParams` and `LowerReturn` type. They must match the type of `self`
    /// for the params/results that are going to be produced. Additionally
    /// these types must be representable with a sequence of `ValRaw` values.
    unsafe fn call_raw<T, Return, LowerParams, LowerReturn>(
        &self,
        mut store: StoreContextMut<'_, T>,
        lower: impl FnOnce(
            &mut LowerContext<'_, T>,
            InterfaceType,
            &mut MaybeUninit<LowerParams>,
        ) -> Result<()>,
        lift: impl FnOnce(&mut LiftContext<'_>, InterfaceType, &LowerReturn) -> Result<Return>,
    ) -> Result<Return>
    where
        LowerParams: Copy,
        LowerReturn: Copy,
    {
        let export = self.lifted_core_func(store.0);

        let (options_idx, flags, ty, raw_options) = self.abi_info(store.0);
        let post_return = raw_options
            .post_return
            .map(|i| self.instance.id().get(store.0).runtime_post_return(i));
        let instance = self.instance.runtime_instance(raw_options.instance);
        let async_ = raw_options.async_;

        store.0.enter_guest_sync_call(async_, instance)?;

        #[repr(C)]
        union Union<Params: Copy, Return: Copy> {
            params: Params,
            ret: Return,
        }

        let space = &mut MaybeUninit::<Union<LowerParams, LowerReturn>>::uninit();

        // Double-check the size/alignment of `space`, just in case.
        //
        // Note that this alone is not enough to guarantee the validity of the
        // `unsafe` block below, but it's definitely required. In any case LLVM
        // should be able to trivially see through these assertions and remove
        // them in release mode.
        let val_size = mem::size_of::<ValRaw>();
        let val_align = mem::align_of::<ValRaw>();
        assert!(mem::size_of_val(space) % val_size == 0);
        assert!(mem::size_of_val(map_maybe_uninit!(space.params)) % val_size == 0);
        assert!(mem::size_of_val(map_maybe_uninit!(space.ret)) % val_size == 0);
        assert!(mem::align_of_val(space) == val_align);
        assert!(mem::align_of_val(map_maybe_uninit!(space.params)) == val_align);
        assert!(mem::align_of_val(map_maybe_uninit!(space.ret)) == val_align);

        Func::with_lower_context(
            self.instance,
            store.as_context_mut(),
            options_idx,
            ty,
            |cx, ty| lower(cx, ty, map_maybe_uninit!(space.params)),
        )?;

        // SAFETY: We are providing the guarantee that all the inputs are valid.
        // The various pointers passed in for the function are all valid since
        // they're coming from our store, and the `params_and_results` should
        // have the correct layout for the core wasm function we're calling.
        // Note that this latter point relies on the correctness of this module
        // and `ComponentType` implementations, hence `ComponentType` being an
        // `unsafe` trait.
        unsafe {
            crate::Func::call_unchecked_raw(
                &mut store,
                export,
                NonNull::new(core::ptr::slice_from_raw_parts_mut(
                    space.as_mut_ptr().cast(),
                    mem::size_of_val(space) / mem::size_of::<ValRaw>(),
                ))
                .unwrap(),
                UncaughtException::Trap,
            )?;
        }

        // Validate that the task, after returning, has no more active borrows
        // as they're required to have been dropped by this point.
        store
            .0
            .component_resource_tables(Some(self.instance))?
            .validate_scope_exit()?;

        // SAFETY: We're relying on the correctness of the structure of
        // `LowerReturn` and the type-checking performed to acquire the
        // `TypedFunc` to make this safe. It should be the case that
        // `LowerReturn` is the exact representation of the return value when
        // interpreted as `[ValRaw]`, and additionally they should have the
        // correct types for the function we just called (which filled in the
        // return values).
        let ret: &LowerReturn = unsafe { map_maybe_uninit!(space.ret).assume_init_ref() };

        let val = Func::with_lift_context(self.instance, store.0, options_idx, ty, |cx, ty| {
            lift(cx, ty, ret)
        })?;

        // SAFETY: it's a contract of this function that `LowerReturn` is an
        // appropriate representation of the result of this function.
        let ret_slice = unsafe { storage_as_slice(ret) };
        let post_return_arg = match ret_slice.len() {
            0 => ValRaw::i32(0),
            1 => ret_slice[0],
            _ => unreachable!(),
        };

        // SAFETY: `post_return` and `flags` were resolved from this function's
        // own canonical options above, and `store` is the store this call is
        // running in.
        unsafe {
            call_post_return(&mut store, post_return, post_return_arg, flags)?;
        }
        store.0.exit_guest_sync_call()?;

        Ok(val)
    }

    #[doc(hidden)]
    #[deprecated(note = "no longer needs to be called; this function has no effect")]
    pub fn post_return(&self, _store: impl AsContextMut) -> Result<()> {
        Ok(())
    }

    #[doc(hidden)]
    #[deprecated(note = "no longer needs to be called; this function has no effect")]
    #[cfg(feature = "async")]
    pub async fn post_return_async(&self, _store: impl AsContextMut<Data: Send>) -> Result<()> {
        Ok(())
    }

    pub(crate) fn lower_args<T>(
        cx: &mut LowerContext<'_, T>,
        params: &[Val],
        params_ty: InterfaceType,
        dst: &mut [MaybeUninit<ValRaw>],
    ) -> Result<()> {
        let params_ty = match params_ty {
            InterfaceType::Tuple(i) => &cx.types[i],
            _ => unreachable!(),
        };
        if params_ty.abi.flat_count(MAX_FLAT_PARAMS).is_some() {
            let dst = &mut dst.iter_mut();

            params
                .iter()
                .zip(params_ty.types.iter())
                .try_for_each(|(param, ty)| param.lower(cx, *ty, dst))
        } else {
            Self::store_args(cx, &params_ty, params, dst)
        }
    }

    fn store_args<T>(
        cx: &mut LowerContext<'_, T>,
        params_ty: &TypeTuple,
        args: &[Val],
        dst: &mut [MaybeUninit<ValRaw>],
    ) -> Result<()> {
        let size = usize::try_from(params_ty.abi.size32).unwrap();
        let ptr = cx.realloc(0, 0, params_ty.abi.align32, size)?;
        let mut offset = ptr;
        for (ty, arg) in params_ty.types.iter().zip(args) {
            let abi = cx.types.canonical_abi(ty);
            arg.store(cx, *ty, abi.next_field32_size(&mut offset))?;
        }

        dst[0].write(ValRaw::i64(ptr as i64));

        Ok(())
    }

    pub(crate) fn lift_results<'a, 'b>(
        cx: &'a mut LiftContext<'b>,
        results_ty: InterfaceType,
        src: &'a [ValRaw],
        max_flat: usize,
    ) -> Result<Box<dyn Iterator<Item = Result<Val>> + 'a>> {
        let results_ty = match results_ty {
            InterfaceType::Tuple(i) => &cx.types[i],
            _ => unreachable!(),
        };
        if results_ty.abi.flat_count(max_flat).is_some() {
            let mut flat = src.iter();
            Ok(try_new::<Box<_>>(
                results_ty
                    .types
                    .iter()
                    .map(move |ty| Val::lift(cx, *ty, &mut flat)),
            )?)
        } else {
            let iter = Self::load_results(cx, results_ty, &mut src.iter())?;
            Ok(try_new::<Box<_>>(iter)?)
        }
    }

    fn load_results<'a, 'b>(
        cx: &'a mut LiftContext<'b>,
        results_ty: &'a TypeTuple,
        src: &mut core::slice::Iter<'_, ValRaw>,
    ) -> Result<impl Iterator<Item = Result<Val>> + use<'a, 'b>> {
        // FIXME(#4311): needs to read an i64 for memory64
        let ptr = usize::try_from(src.next().unwrap().get_u32())?;
        if ptr % usize::try_from(results_ty.abi.align32)? != 0 {
            bail!("return pointer not aligned");
        }

        let bytes = cx
            .memory()
            .get(ptr..)
            .and_then(|b| b.get(..usize::try_from(results_ty.abi.size32).unwrap()))
            .ok_or_else(|| crate::format_err!("pointer out of bounds of memory"))?;

        let mut offset = 0;
        Ok(results_ty.types.iter().map(move |ty| {
            let abi = cx.types.canonical_abi(ty);
            let offset = abi.next_field32_size(&mut offset);
            Val::load(cx, *ty, &bytes[offset..][..abi.size32 as usize])
        }))
    }

    #[cfg(feature = "component-model-async")]
    pub(crate) fn instance(self) -> Instance {
        self.instance
    }

    /// Creates a `LowerContext` using the provided configuration values and runs
    /// the given `lower` closure within it.
    ///
    /// The `lower` closure provided should perform the actual lowering and
    /// return the result of the lowering operation which is then returned from
    /// this function as well.
    pub(crate) fn with_lower_context<T>(
        instance: Instance,
        mut store: StoreContextMut<T>,
        options: OptionsIndex,
        ty: TypeFuncIndex,
        lower: impl FnOnce(&mut LowerContext<T>, InterfaceType) -> Result<()>,
    ) -> Result<()> {
        let mut cx = LowerContext::new(store.as_context_mut(), options, instance);
        let param_ty = InterfaceType::Tuple(cx.types[ty].params);
        lower(&mut cx, param_ty)
    }

    /// Creates a `LiftContext` using the provided configuration values and runs
    /// the given `lift` closure within it.
    ///
    /// The closure `lift` provided should actually perform the lift itself and
    /// the result of that closure is returned from this function call as well.
    pub(crate) fn with_lift_context<R>(
        instance: Instance,
        store: &mut StoreOpaque,
        options: OptionsIndex,
        ty: TypeFuncIndex,
        lift: impl FnOnce(&mut LiftContext, InterfaceType) -> Result<R>,
    ) -> Result<R> {
        let mut cx = LiftContext::new(store, options, instance)?;
        let ty = InterfaceType::Tuple(cx.types[ty].results);
        lift(&mut cx, ty)
    }
}

pub(crate) unsafe fn call_post_return(
    mut store: impl AsContextMut,
    func: Option<NonNull<VMFuncRef>>,
    arg: ValRaw,
    mut flags: InstanceFlags,
) -> Result<()> {
    unsafe {
        // Post return functions are forbidden from calling imports or
        // intrinsics.
        flags.set_may_leave(false);

        // If the function actually had a `post-return` configured in its
        // canonical options that's executed here.
        if let Some(func) = func {
            crate::Func::call_unchecked_raw(
                &mut store.as_context_mut(),
                func,
                core::slice::from_ref(&arg).into(),
                UncaughtException::Trap,
            )?;
        }

        // And finally if everything completed successfully then the "may
        // leave" flags is set to `true` again here which enables further
        // use of the component.
        flags.set_may_leave(true);
    }

    Ok(())
}