[SAoC] New proposal: solve dependency hell for dub

[Joseph Rushton Wakeling]

On Monday, 12 August 2019 at 11:20:53 UTC, Seb wrote:
> This was my personal opinion.

It would be good if you could highlight opinions as such -- 
you're a figure of some authority and standing here, so if you 
say something like "it's vital" it's good to be clear whether 
this is something collectively agreed or not.

In particular, the arguments why this is a _requirement_ to move 
phobos to DUB need to be really clearly laid out in the proposal.

> Also, as far as I am aware the Rust solution has been extremely 
> successful for them and a vital part of their flourishing 
> ecosystem. I'm open to better solutions though ;-)

Just because Rust has a flourishing ecosystem, does not 
necessarily mean that we should just copy the surface details of 
what they do ;-)

It really feels like this approach works around one set of 
problems (which are mostly library maintenance problems) while 
opening up a whole can of others (e.g. what happens when you get 
multiple versions of libraries that expect to be the sole owner 
of some important program component, such as a task scheduler?).

I don't object per se to the idea of customizable mangling (in 
particular I like that the proposed solution is not 
DUB-specific), but before rolling that into DUB as a dependency 
resolution system, I think it would be really helpful to first 
resolve the existing issues with single dependency resolution.

One particular thing I'd like to understand about the proposal: 
how does the custom mangling interact with templates?

Suppose I have v1.x and v2.x of some project, and both versions 
define (an identical) SomeTemplate, and that's used in my 
project.  Given how templates are incorporated into programs 
(i.e. we can't pre-build it at the build-library stage, it's 
instantiated only when the main program is built), how is it 
decided which version's template to use, and hence which mangling 
will be used?