Method call_impl

crates/wasmtime/src/runtime/component/func.rs:306–362

(
        &self,
        mut store: impl AsContextMut,
        params: &[Val],
        results: &mut [Val],
    )

    }

    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.abi_async(store.0) {
            unreachable!(
                "async-lifted exports should have failed validation \
                 when `component-model-async` feature disabled"
            );
        }

        // 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 (_, post_return_arg) = 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(())
                },
            )?
        };

        self.post_return_impl(store, post_return_arg)
    }