ReadOnlyMemory<T> rewrites to ReadOnlySpan<T> across yield

[PetarIsakovic]

[Zomp.SyncMethodGenerator.CreateSyncVersion] generates invalid sync code for an async iterator method that uses ReadOnlyMemory<T> and yield return.

The generated method rewrites a ReadOnlyMemory<T> local into ReadOnlySpan<T> inside an iterator and emits assignments that don’t type-check.

Minimal repro

using System;
using System.Collections.Generic;
using System.Runtime.CompilerServices;
using System.Threading;

public static partial class Repo
{
    [Zomp.SyncMethodGenerator.CreateSyncVersion]
    public static async IAsyncEnumerable<int> Foo(IAsyncEnumerable<ReadOnlyMemory<bool>> input, [EnumeratorCancellation] CancellationToken ct = default)
    {
        ReadOnlyMemory<bool> prev = default;
        var hasPrev = false;

        await foreach (var col in input.WithCancellation(ct))
        {
            if (hasPrev)
            {
                Helper(prev, col);
            }

            prev = col;
            hasPrev = true;

            yield return 1;
        }
    }

    private static void Helper(ReadOnlyMemory<bool> a, ReadOnlyMemory<bool> b) { }
}