cyclic redundancy

[Steven Schveighoffer]

On 6/18/18 3:19 AM, Mr.Bingo wrote:
> I have static this scattered throughout. Some are module static this and 
> some are struct and class.
> 
> 
> In a test case I have reduced to a struct that uses a static this and I 
> get a cycle... even though, of course, the static this does nothing 
> accept internal things.
> 
> It is very annoying to have to hack these cycles. while they can be 
> bypassed for testing but production requires passing a runtime argument 
> which is useless for distribution to users.
> 
> The cyclic testing is so ignorant that it effectively makes using any 
> static this with any type of complex importing impossible, even though 
> no cycles actually exist.

Indeed, the module dependency information is very coarse, so it's very 
easy to have "fake" cycles. All we look at is which modules import other 
modules.

Note that the cycle detection and ordering is correct, given the limited 
information the compiler provides.

> Something new has to be done.
> 
> I propose that some way be made to disable a static this from being 
> included in the testing:
> 
> @NoCyclicRedundancyCheck static this()
> {
> 
> }

I'd love to see something like this. Note that the cycle check is not 
for redundancy, but for ordering how to call the static ctors. What you 
really want to call this is @IndependentCtor or something like that. 
This means that this segment of the static ctor does not depend on 
anything initialized by other static ctors, and so can be called at any 
time.

> I'm not sure if attributes will persist at runtime though. Any method is 
> better than what we have now which essentially prevents all static this 
> usage because one can't guarantee that the future won't create a cycle 
> and then the program will break with no easy fix.

It would effectively split the static ctors into 2 functions, one that 
can be called independently, and one that has to be sorted. How this is 
normally handled is the compiler makes "fake" modules so it can put that 
moduleinfo somewhere.

-Steve