fix Issue 23606 - betterC with CTFE and gc

[WalterBright]

The comment says it won't work. Let's see what happens.

[dlang-bot]

Thanks for your pull request, @WalterBright!

Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	23606	normal	betterC with CTFE and gc

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "master + dmd#14791"

[WalterBright]

The missing symbol errors all seem to be instantiations of Object.RTInfoImpl

[WalterBright]

Boiled the problem down to this:

class C {  int a,b,c;   int* p,q; }
void test() {    C c = new C(); }

which does not put the RTInfoIml in the object file which it should.

[WalterBright]

Ok, I abandoned the last approach for a new one. This allows GC operations to be done in betterC, but any functions that do them are not emitted to the object file. This enables them to be used for CTFE.

[WalterBright]

The Azure failure looks unrelated.

[dkorpel]

This is redundant with FUNCFLAG.isCompileTimeOnly

[WalterBright]

Unfortunately, isCompileTimeOnly doesn't do what it says it does. That logic is a mess. So I avoided it pending a future refactoring.

[dkorpel]

With a nested function, you can remove the duplicated branches which aren't covered by tests.

[ibuclaw]

Bug fixes should really target stable.

[RazvanN7]

The problem with this approach is that you might have a template function that is GC and is both used at compile at and runtime. What will happen in this case: you get a link error that leaves you scratching your head.

Also, this seems to have caused a regression: https://issues.dlang.org/show_bug.cgi?id=23799

[RazvanN7]

Actually, Issue 23799 has simply been exposed by this implementation. However, this has caused another regression:

string foo()()
{
    string a, b;
    return a ~ b;
}

enum s = foo();

extern(C) void main()
{
    foo();                                                                                                              
}

This code used to give a good error message, but now it just fails to link.