Combining #if SYNC_ONLY with if(...) or using(...) ends up with missing code

[persn]

I don't know how well supported #if SYNC_ONLY #else "endif is supposed to be, but if I try doing the following it works perfectly like expected

[Zomp.SyncMethodGenerator.CreateSyncVersion]
public static async Task Foo2Async()
{
#if SYNC_ONLY
    _ = true;
#else
    _ = true;
#endif
    await Task.Delay(100).ConfigureAwait(false);
}

However if I do something that has () like if or using inside the directives it'll lose all code after #endif

[Zomp.SyncMethodGenerator.CreateSyncVersion]
public static async Task FooAsync()
{
#if SYNC_ONLY
    if (true)
#else
    if (true)
#endif
        await Task.Delay(100).ConfigureAwait(false);
}

Because the generated code ends up like this

public static void Foo()
{
    if (true)
}

[lsoft]

@virzak I found that ISG does not like #else at any symbol:

        [Zomp.SyncMethodGenerator.CreateSyncVersion]
        public async Task<T> FooAsync<T>()
        {
#if MY_SPECIAL_SYMBOL
            if (true)
#else
            if (true)
#endif
            { }

            return default;
        }

gives me

        public T Foo<T>()
        {

            return default;
        }

It would be more correct if ISG converts these non-related symbols as is withot touching it:

        public T Foo<T>()
        {
#if MY_SPECIAL_SYMBOL
            if (true)
#else
            if (true)
#endif
            { }

            return default;
        }

I suspect this may become a very difficult task, for example this will fail:

#define MY_SPECIAL_SYMBOL

...

        [Zomp.SyncMethodGenerator.CreateSyncVersion]
        public async Task<T> FooAsync<T>()
        {
#if MY_SPECIAL_SYMBOL
            await Task.Delay(1);
#else
            await Task.Delay(1);
#endif
            return default;
        }

ISG should take a look inside of all branches to convert the code, now it looks only to the active branch, leave the other as is (with async style inside the sync method).

[virzak]

Yes, this is more complex than it seems. I can definitely look into this, however I'm wondering a workaround is feasible?

A statement like this:

#if SYNC_ONLY
    if (true)
#else
    if (true)
#endif
        await Task.Delay(100).ConfigureAwait(false);

would require the generator to construct if statement from disabled trivia.

Would this work for now?

#if SYNC_ONLY
        if (true)
            global::System.Threading.Thread.Sleep(100);
        
#else
        if (true)
            await Task.Delay(100).ConfigureAwait(false);
#endif

[persn]

That probably looks reasonable for a naive one-liner, but in production code there's usually many lines within curly brackets which the code generator handles equally poorly. I should mention that the same problem also happens for usings, so then I would need to copy-paste the same code twice.

Right now it looks like to me that for the methods where this is a problem it's better to not use the code generator at all and just keep and maintain a sync and a async manually.

[GerardSmit]

As workaround: it's also possible to define a constant value in the method like this:

#if SYNC_ONLY
    const bool isAsync = false;
#else
    const bool isAsync = true;
#endif

When C# compiles the if-statements:

if (isAsync) await Task.Delay(100).ConfigureAwait(false);

it sees that isAsync is a constant value, and removed the if-statement in the release build.
See the SharpLab here, you can see that "Async" is not in the decompiled C#-code on the right.