Re: Breaking changes to the base library

20 Jun 2021

      What is the reason that -Wcompat flags are not enabled by -Wall? The
unqualified Data.List import was warned by -Wcompat about since
GHC-8.10, I'm surprised that it still surprise people.

Should -Wcompat be implied by -Wall? Why not? I think that people who
won't ever consider upgrading GHC to be a very very small minority, and
they can suppress these warnings with `-Wall -Wno-compat`.

- Oleg

On 20.6.2021 17.57, Edward Kmett wrote:
...
The breakage concern is why Data.List wound up in its limbo-like state
of re-exporting the Foldable-polymorphic combinators since 7.10 --
while "weird", it was the only option that didn't have to choose
between removing the names from Data.List exports entirely and
breaking unqualified imports of Data.List.
With the monomorphized combinators in place, Data.List should be
considered a 'qualified' import like Data.Map. We definitely need to
do more to communicate that this is changing and how users should
adjust their code to suit. After all, by far the most common intended
import from Data.List is the humble 'sort', which doesn't conflict.
-Edward
On Sun, Jun 20, 2021 at 4:45 AM Chris Smith mailto:cdsmith@gmail.com> wrote:
Yikes, this is going to break nearly everything.  Definitely good
    to let people know.
On Sun, Jun 20, 2021 at 7:43 AM Ben Gamari mailto:ben@smart-cactus.org> wrote:
Harendra Kumar mailto:harendra.kumar@gmail.com> writes:
> I see the following errors when compiling with ghc head version:
        >
        > $ ghc-stage2 --version
        > The Glorious Glasgow Haskell Compilation System, version
        9.3.20210608
        >
        > $ cabal build --with-compiler ghc-stage2 --allow-newer
        >
        > Data/Colour/CIE.hs:80:12: error:
        >     Ambiguous occurrence ‘sum’
        >     It could refer to
        >        either ‘Prelude.sum’,
        >               imported from ‘Prelude’ at
        Data/Colour/CIE.hs:25:8-22
        >               (and originally defined in ‘Data.Foldable’)
        >            or ‘Data.List.sum’,
        >               imported from ‘Data.List’ at
        Data/Colour/CIE.hs:41:1-16
        >               (and originally defined in ‘GHC.List’)
        >    |
        > 80 |    total = sum $ map fst l
        >    |            ^^^
        >
        > Can someone briefly describe this change and what's the
        recommended way of
        > fixing this? Just hide the Data.List definition? I do not
        see this
        > mentioned in the release notes of 9.2/9.4 here:
        >
        https://ghc.gitlab.haskell.org/ghc/doc/users_guide/9.2.1-notes.html
        >
        Indeed, this is due to the monomorphic Data.List proposal,
        which the
        CLC decided would accompany the addition of
        Data.List.singleton. The
        correct fix here is to either qualify the import of
        `Data.List` or add
        an explicit import list. I'll try to remember to add a note
        about this
        to the release notes and migration guide.
Cheers,
- Ben
_______________________________________________
        ghc-devs mailing list
        ghc-devs@haskell.org mailto:ghc-devs@haskell.org
        http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs
_______________________________________________
    ghc-devs mailing list
    ghc-devs@haskell.org mailto:ghc-devs@haskell.org
    http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs
_______________________________________________
ghc-devs mailing list
ghc-devs@haskell.org
http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs

Re: Breaking changes to the base library

Oleg Grenrus