[ghc-steering-committee] Fine-Grained Unused Warnings (#42)

[Chris Dornan]

Thanks Simon, Moritz and Adam,

I asked Jakob to address Simon's and Tom's suggestions, at least to explain why they don't feature in the current draft.

I have also made it clear we need some downstream tooling input.

Personally, I still like the proposal in the current draft and am hoping Jakob will see a way to resolve the points raised by Tom and Simon without too much disruption.

Chris

> On 9 Sep 2023, at 03:12, Moritz Angermann <moritz.angermann at gmail.com> wrote:
> 
> I’m supportive of this proposal. I think Adam raised a good concern on the discussion with respect to tooling. As this does not impact GHCs acceptance of existing code, I’m more lenient towards these changes.
> 
> Moritz
> 
> On Sat, 9 Sep 2023 at 5:43 AM, Simon Peyton Jones <simon.peytonjones at gmail.com <mailto:simon.peytonjones at gmail.com>> wrote:
>> I'm supportive of this proposal in general -- that is, make it easy to find what the "root" unused bindings are, without cluttering up the warnings with all the transitively unused ones.
>> 
>> But I have a question (added on the discussion thread) about the ergonomics.
>> 
>> On Fri, 8 Sept 2023 at 03:16, Chris Dornan <chris at chrisdornan.com <mailto:chris at chrisdornan.com>> wrote:
>>> Proposal: Fine-Grained Unused Warnings (#42)
>>> Author: Jakob Brünker
>>> Rendered proposal: https://github.com/JakobBruenker/ghc-proposals/blob/fine-grained-unused/proposals/0000-fine-grained-unused-warnings.rst
>>> Discussion: https://github.com/ghc-proposals/ghc-proposals/pull/434
>>> Recommendation: Acceptance
>>> 
>>> ## Summary
>>> 
>>> GHC currently warns equally about any superfluous binding that it discovers, regardless of whether
>>> the definition is unreferenced anywhere itself, or is merely mentioned by other definitions that are
>>> similarly superfluous. The proposal proposes to replace these warnings with just the warnings about
>>> definitions that are not referenced anywhere, but list within those warnings the entities it
>>> references that would otherwise not be required. The same information is being conveyed under this
>>> proposal as previously, but in a more structured manner.
>>> 
>>> The proposal is careful to ensure the -Wunused-* controls (-Wunused-top-binds, etc.) are respected,
>>> so the subwarnings of transitively unused entities are only listed if their corresponding -Wunused-*
>>> control is active.
>>> 
>>> As Jakob points out in the proposal, getting these warnings into some structure is partly motivated
>>> by IDE usage where the 'additional [transitive] warnings take up a lot of valuable screen real
>>> estate'.
>>> 
>>> ## Example [From the proposal]
>>> 
>>>     In the following code,
>>> 
>>>         module Foo ()
>>> 
>>>         import Data.List as L
>>> 
>>>         foo = L.intercalate
>>> 
>>>     `intercalate` is transitively unused, since it is only used by `foo`, which is unused. The warning
>>>     that's produced will be
>>> 
>>>         Foo.hs:5:1: warning: [-Wunused-top-binds]
>>>             Defined but not used: ‘foo’
>>>             as a consequence the following imports are transitively unused [-Wunused-imports]:
>>>               Data.List imported at foo.hs:3:1:
>>> 
>>>     The warning about transitively unused bindings only appears if both the warning flag for the unused binding (in this case -Wunused-top-binds) and the the one for the transitively unused binding itself (in this case -Wunused-imports) are enabled.
>>> 
>>> 
>>> ## Recommendation
>>> 
>>> This proposal is not at all disruptive (arguably to the extent of not requiring a GHC proposal
>>> review), is well thought out, and can improve the GHC/IDE UI so I recommend that we accept it.
>>> 
>>> _______________________________________________
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