[ghc-steering-committee] Please review: #454 Custom type warnings

[Vladislav Zavialov (int-index)]

Can we guarantee erasure? Is `Warning flag msg => t` the same operationally as just `t`?

The proposal does not say that. And it’s not what I would’ve expected from a constraint. Yet it’s something I expect from a warning.

I am not comfortable with a design where adding a custom warning, the purpose of which is to improve developer experience, comes at a cost of potential performance regression.

This isn’t a trade off that users of GHC should be facing.

- Vlad

> On 14 Jan 2022, at 00:47, Richard Eisenberg <lists at richarde.dev> wrote:
> 
> I vote to accept.
> 
> Thanks,
> Richard
> 
>> On Jan 13, 2022, at 11:19 AM, Tom Harding <i.am.tom.harding at gmail.com> wrote:
>> 
>> Hi all,
>> 
>> As Joachim noted, #454 is extracted from Adam’s previous efforts with the Unsatisfiable constraint proposal (which has since been accepted). In short, it covers an interface for custom warnings, and I can already think of plenty of ways I’d use it. I’d therefore like to recommend acceptance, and discuss any issues or changes.
>> 
>> Thanks,
>> Tom
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