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

[Moritz Angermann]

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> 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> 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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