[dub-reference/dependencies] For Have_x versions, be clear that these should ONLY be used to tell if a dependency is present

[WebFreak001]

@schveiguy

Using the Have_x versions should have the possible drawbacks discussed.

If you use version(Have_x), then that version might be defined when importing modules from a project, even if the project does not have a dependency on x. This can lead to bizarre behaviors like versioning out symbols that look like they should be present, resulting in linker errors.

A dependency is never built with Have_x unless x is actually a dependency.

I'm not sure how to describe this in a concise or non-confusing fashion. Maybe a simple example.

The current dub documentation is very sparse on the subject.

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@WebFreak001

A dependency is never built with Have_x unless x is actually a dependency.

wait do you mean that x is a direct dependency? (optional or not)

I think it would probably rather be a bug if it was included without it being a direct dependency. (optional or not)

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@schveiguy

Not direct, but a dependency. The example from discord was something like:

module b; // project b
version(Have_a) int x;

And then in project a, it thinks there's an x int variable when it imports b, but when b is built, it omits that. This is because b doesn't build with Have_a as a version.

If a becomes a dependency of b, then it is OK.

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@WebFreak001

ah right, a note / warning for this would probably be nice on the documentation page then.

It's probably a bug that the dependency even has that version (Have_a) statement without having a as dependency, as it would always be false then.

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@schveiguy

Right, that int will never be defined. That's probably the easiest way to explain it.