Argh!! Cyclic dependencies!!!

[Steven Schveighoffer]

On Fri, 18 Mar 2011 17:42:58 -0400, Nick Sabalausky <a at a.a> wrote:

> These module constructor "Cyclic dependencies" errors are really  
> starting to
> piss me off. I feel like I'm back in the days when you'd sneeze and DMD
> would vomit out 100 forward reference errors just because you didn't  
> write
> your whole damn app in one giant ultra-module. (/me takes a breather to
> chill out...Ok...)
>
> I don't suppose there's any chance we could get a quick little:
>
> import foo;
>
> pragma(staticCtorsAvoid, foo);
> // Or
> pragma(staticCtorsRunBefore, foo);
> // Or
> pragma(staticCtorsRunAfter, foo);
>
> static this()
> {
>     // do trivial shit that doesn't touch foo
> }
>
> Could we? I don't care which it is. I don't care if it doesn't enforce  
> any
> safety at all. I don't care if it gets depricated in favor of an  
> alternate
> solution in a later version. I just need a way to say "this'll work, dmd,
> just do it and quit yer damn whinin'!!" Doesn't need to be perfect, just
> needs to work. At the very least, if I manage to be able to hack  
> something
> like that it in, would there be any chance of it getting accepted?

If you are interested, the code that runs the static ctors is in druntime,  
not the compiler.  So you can turn off the errors if you want in your  
local copy of druntime.

FWIW, there is a "standalone" flag which allows you to skip cycle  
detection on that module.  I'm not quite sure why the compiler sets that  
flag, but it has something to do with little modules created by the  
compiler itself.  When I rewrote the cycle detection code, I used to have  
an idea of why, but it's faded from my memory.

In any case, I think you could do something repulsive like naming your  
module nodeps_x instead of x, and have the cycle detection skip over that  
module when detecting cycles.  Bottom line is, there is no valid static  
data before static ctors run, so you must figure out how to get the info  
to the cycle detection routine without static data.

If we are changing the compiler, I'd like this:

@standalone module foo;

which would tell the compiler to set the standalone flag, no proof  
required.  I don't think it's really possible to verify that a static ctor  
does not depend on outside data without full analysis which isn't  
currently possible.

-Steve