[Haskell-cafe] Versioning of libraries bundled with GHC pre-releases

Oleg Grenrus oleg.grenrus at iki.fi
Tue Jan 16 20:14:22 UTC 2018

Hi Ben,

Note that PVP dictates to do _major_ bump every time a breaking changes
is introduced:

1. Breaking change. If any entity was removed, or the types of any
entities or the definitions of datatypes or classes were changed, or
orphan instances were added or any instances were removed, then the
new A.B MUST be greater than the previous A.B.

This means that first alpha-release for e.g. GHC-8.4.1/base- or
GHC-8.6.1/base- will force to freeze both GHC and base.

For example "Make the Div and Mod type families `infixl 7`" commit
is a breaking change. OTOH it's pity not to fix new feature before it's
officially released.

I cannot judge how much ghc-the-lib public API changes.

TL;DR first alpha release is too early to do "PVP dictated freeze".

I think that we need *staging* (mutable) package repository, where
package authors can upload packages using lighter release procedure.
Let's keep Hackage to high standards, and test in a staging environment,
not the production one.

- Oleg

On 16.01.2018 20:35, Ben Gamari wrote:
> TL;DR. We propose to start following the PVP for core libraries shipped
>        with GHC alpha release. Let us know what you think.
> Hello everyone,
> GHC has recently been reworking its release policy, increasing the
> release cadence to two releases per year. We hope that this change
> facilitates earlier and more thorough testing of GHC. Of course,
> a compiler is worth little if no real-world packages can be built with
> it.
> Historically library maintainers have been reluctant to offer releases
> claiming compatibility with pre-release GHCs due to the lax versioning
> guarantees offered by such pre-releases. Specifically, changes to
> libraries shipped with GHC pre-releases have historically not had
> proper distinct version numbers, causing unnecessary breakage for
> released code (e.g. [1]).
> To make maintainers feel more at ease with releasing libraries
> compatible with GHC alpha releases, we propose to start using the
> Package Versioning Policy (PVP) [2] to version GHC's core libraries with
> each alpha release. That is, libraries which are not source-identical
> will get at very least a minor bump with each alpha release.
> By "core libraries" we mean the set of:
>  * base
>  * template-haskell
>  * integer-gmp
>  * integer-simple
>  * hpc
>  * ghci
>  * ghc-compact
>  * all GHC dependencies not maintained by GHC HQ
>  * ghc-prim
>  * ghc-boot
>  * ghc-boot-th
> Following the PVP will allow maintainers to safely release libraries to
> Hackage without fear that they will break when the final GHC 8.4.1
> release is made, easing the testing process for everyone.
> If you have an opinion one way or another on this matter please do share
> it on this list.
> Cheers,
> - Ben
> [1] https://github.com/tibbe/hashable/issues/143
> [2] https://pvp.haskell.org/
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