[swift-evolution] Make non-void functions @warn_unused_result by default

[Janosch Hildebrand]

No worries, there should be plenty of time for discussion.

Swift 3 contains many changes that will require libraries to be updated anyway, so I don’t think this would prove to be an undue burden.
But yes, weighing cost vs. benefit will certainly be part of the proposal evaluation.

As for whom we want to help, it’s predominantly API users.
Ideally every function would be perfectly annotated but ultimately not every API developer will know about, remember or put in the effort to annotate with @warn_unused_result. Making the inverse the default should hopefully be “safer” by warning by default.

Extraneous warnings are also much more obvious than missing warnings, encouraging potential annotation.

The expectation that many if not most functions (with return values) should warn is, I believe, mostly motivating in the sense of hopefully making this change (more) palatable.

- Janosch

> On 24 Feb 2016, at 23:47, Gwendal Roué <gwendal.roue at gmail.com> wrote:
> 
> Oh yes please, don't rush on this...
> 
> Who do we want to help here? API users, or API developers?
> 
> Considering that Swift may be on the verge of a great breakthrough, plenty of immature yet popular libraries will ship. Plenty have already shipped. This is a great sign of vitality. Should @warn_unused_result become the default, the quality of the code of the users of those libraries risks a brutal degradation, full of poor `let _ = ...`.
> 
> Gwendal
> 
>> Le 24 févr. 2016 à 16:01, Jean-Daniel Dupas via swift-evolution <swift-evolution at swift.org> a écrit :
>> 
>> IMHO, before any decision, it may be interesting to write a quick patch and run the modified compiler on real code to see how much false positive it would generate.
>> 
>>> Le 24 févr. 2016 à 16:13, Janosch Hildebrand via swift-evolution <swift-evolution at swift.org> a écrit :
>>> 
>>> Erica's proposal about "Modernizing Attribute Case and Attribute Argument Naming" made me remember this discussion.
>>> 
>>> I don't think a proposal was ever submitted? If no one else is working on a proposal already I would offer myself up for writing this up.
>>> 
>>> - Janosch
>>> 
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