fix issue 13262 - Cannot send certain shared data to another thread

[schveiguy]

There were 2 major issues:

1. Variant was not properly removing the shared qualifier when copying data from the stack into the payload (this is always safe, as the Variant itself is not shared, so the payload, which is never accessible by reference, is also not actually shared).
2. std.traits.ImplicitConversionTargets incorrectly returned const(T)[] as a valid conversion target for shared(T)[]. It should have been const(shared(T))[].

All the tests for the bug were ported to verifying Variant could accept the types, and this in turn fixes the send and receive functions (I added one unit test to verify the original test case to std/concurrency.d).

[dlang-bot]

Thanks for your pull request, @schveiguy!

Bugzilla references

Auto-close	Bugzilla	Description
✓	13262	Cannot send certain shared data to another thread

[MetaLang]

Variant was not properly removing the shared qualifier when copying data from the stack into the payload (this is always safe, as the Variant itself is not shared, so the payload, which is never accessible by reference, is also not actually shared).

What if the user creates a shared Variant?

[schveiguy]

What if the user creates a shared Variant?

Then nothing will work I think :)

[schveiguy]

In other words, if you create a shared(Variant), you have to cast away shared to do any operations, so you better know what you are doing.

[atilaneves]

It might be good to ensure that a struct that does have a shared postblit can be used.

[schveiguy]

I tried. It can't, but not because of this code, there are a whole bunch of places where it fails. I didn't want to fix everything 😉

[atilaneves]

Fair enough :)

[atilaneves]

LGTM

[schveiguy]

I've updated to avoid using typeid's destroy and postblit anywhere, since these do not take into account whether the postblit and destructor are properly attributed. This should eliminate some invalid types from being incorrectly used.

[wilzbach]

Thanks!