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<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif">Dear GHC devops group<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif">The conversation on
<a href="https://ghc.haskell.org/trac/ghc/ticket/14558">Trac #14558</a> suggests that we might want to consider reviewing
<a href="https://ghc.haskell.org/trac/ghc/wiki/WorkingConventions/Releases">GHC’s release policies</a>. This email is to invite your input.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif">The broad questions is this. We want GHC to serve the needs of all its users, including downstream tooling that uses GHC. What release policies will best support that goal? For example, we
already ensure that GHC 8.4 can be compiled with 8.2 and 8.0. This imposes a slight tax on GHC development, but it means that users don't need to upgrade quite as often. (If the tempo of releases increases, we might want to increase the window.)<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif">Trac #14558 suggests that we might want to ensure the metadata on GHC’s built-in libraries is parsable with older Cabals. One possibility would be this:<o:p></o:p></span></p>
<ul style="margin-top:0cm" type="disc">
<li class="MsoListParagraph" style="margin-left:0cm;mso-list:l1 level1 lfo1"><span style="font-family:"Calibri",sans-serif">Ensure that the Cabal metadata of non-reinstallable packages (e.g. integer-gmp) shipped with GHC be parsable by the Cabal versions shipped
with the last two major GHC releases [i.e. have a sufficiently old cabal-version field]. That is, in general a new Cabal specification will need to be shipped with two GHC releases before GHC will use start using its features in non-reinstallable packages.<o:p></o:p></span></li><li class="MsoListParagraph" style="margin-left:0cm;mso-list:l1 level1 lfo1"><span style="font-family:"Calibri",sans-serif">Upholding this policy won't always be possible. There may be cases (as is the case Hadrian for GHC 8.4) where the benefit of quickly
introducing incompatible syntax outweighs the need for compatibility. In this (hopefully rare) case we would explicitly advertise the incompatibility in the release documentation, and give as much notice as possible to users to allow downstream tools to adapt.<o:p></o:p></span></li><li class="MsoListParagraph" style="margin-left:0cm;mso-list:l1 level1 lfo1"><span style="font-family:"Calibri",sans-serif">For reinstallable packages, of which GHC is simply a client (like text or bytestring), we can’t reasonably enforce such a policy, because
GHC devs have no control over what the maintainers of external core libraries put in their Cabal files.<o:p></o:p></span></li></ul>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif">This is just a proposal. The narrow questions are these:<o:p></o:p></span></p>
<ul style="margin-top:0cm" type="disc">
<li class="MsoListParagraph" style="margin-left:0cm;mso-list:l0 level1 lfo2"><span style="font-family:"Calibri",sans-serif">Would this be sufficient to deal with the concerns raised in #14558?<o:p></o:p></span></li><li class="MsoListParagraph" style="margin-left:0cm;mso-list:l0 level1 lfo2"><span style="font-family:"Calibri",sans-serif">Is it necessary, ow would anything simpler be sufficient?<o:p></o:p></span></li><li class="MsoListParagraph" style="margin-left:0cm;mso-list:l0 level1 lfo2"><span style="font-family:"Calibri",sans-serif">What costs would the policy impose on GHC development?<o:p></o:p></span></li><li class="MsoListParagraph" style="margin-left:0cm;mso-list:l0 level1 lfo2"><span style="font-family:"Calibri",sans-serif">There may be matters of detail: e.g. is two releases the right grace period. Would one do?<o:p></o:p></span></li></ul>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif">Both the broad question and the narrow ones are appropriate for the Devops group.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif">Thanks!<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif">Simon<o:p></o:p></span></p>
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