I think we just go ahead and rename the constructor. We don't have back-compat guarantees at this level. Simplicity is a virtue, too!
Thanks, Richard > On Jul 6, 2021, at 5:59 AM, Alfredo Di Napoli <alfredo.dinap...@gmail.com> > wrote: > > > Hello Simon, > > Yes, renaming and perhaps keeping `RecordPuns` as a pattern synonym to not > break backward-compat, if that's feasible to define as we are in > `ghc-boot-th` here. Not sure if `PatternSynonyms` and `COMPLETE` would be > available there. > > I am not sure how many libs that depend on the ghc API would break (I haven't > grepped on Hackage yet), but that might tip the benefits/troubles ratio > towards keeping the status quo. > > This is not a "problem" I have to solve today, and it might not be considered > a problem by others (just an inconsistency I guess): as a colleague of mine > pointed out, GHC is not necessarily "lying" here. It's still the same > underlying extension, it just happens that there are two names that refer to > it. > > Perhaps I could think about adding to `GhcHint` some kind of mapping which > would give to IDEs or third-party libs the correct extension name given an > input `LangExt.Extension`, the problem then becomes making sure that we keep > this mapping in sync with the information contained in `GHC.Driver.Session`. > > I will let it simmer. > > Thanks! > > A. > > On Tue, 6 Jul 2021 at 11:19, Simon Peyton Jones <simo...@microsoft.com > <mailto:simo...@microsoft.com>> wrote: > 1. What prevents us from adding `NamedFieldPuns` as a proper constructor for > the `Extension` type and in principle remove `RecordPuns`? Backward > compatibility I assume? > > You mean, essentially, rename `LangExt.RecordPuns` to `NamedFieldPuns`. > > > > I’d be fine with that. There might be back-compat issues, but only with > other plugins, and probably with vanishingly few of them. Grep in Hackage! > > > > Simon > > > > From: ghc-devs <ghc-devs-boun...@haskell.org > <mailto:ghc-devs-boun...@haskell.org>> On Behalf Of Alfredo Di Napoli > Sent: 06 July 2021 10:14 > To: Simon Peyton Jones via ghc-devs <ghc-devs@haskell.org > <mailto:ghc-devs@haskell.org>> > Subject: Can NamedFieldPuns be added to > `GHC.LanguageExtensions.Types.Extension`? > > > > Dear all, > > > > As some of you might know, for the past few months I have been working on > changing GHC's diagnostic messages from plain SDocs to richer Haskell types. > > > > As part of this work, I have added a mechanism to embed hints into > diagnostics, defined in `GHC.Types.Hint` in `HEAD`. One of the main workhorse > of this `GhcHint` type is the `SuggestExtension LangExt.Extension` > constructor, which embeds the extension to enable to use a particular > feature. The `LangExt.Extension` type comes from > `GHC.LanguageExtensions.Types`, and up until now there has always been a 1:1 > mapping between the language pragma for the extension and the type itself. > > > > Today I was working on turning this error into a proper Haskell type: > > > > badPun :: Located RdrName -> TcRnMessage > > badPun fld = TcRnUnknownMessage $ mkPlainError noHints $ > > vcat [text "Illegal use of punning for field" <+> quotes (ppr fld), > > text "Use NamedFieldPuns to permit this"] > > > > I was ready to yield a `SuggestExtension LangExt.NamedFieldPuns` when I > discovered that there is no `NamedFieldPuns` constructor. Rather, there is a > `RecordPuns` , which refer to a deprecated flag, and we simply map > `NamedFieldPuns` back to it in `GHC.Driver.Session`: > > > > ... > > depFlagSpec' "RecordPuns" LangExt.RecordPuns > > (deprecatedForExtension "NamedFieldPuns"), > > ... > > flagSpec "NamedFieldPuns" LangExt.RecordPuns, > > ... > > > > This is problematic for the `GhcHint` type, because now if I was to yield > `SuggestExtension LangExt.RecordPuns` to the user, I could still pretty-print > the suggestion to turn `RecordPuns` into `NamedFieldPuns`, but this means > that IDEs or third-party library would have access to the > > "raw" Haskell datatype, and at that point they will be stuck with a > suggestion to enable a deprecated extension! (or best case scenario they will > have to transform the suggestion into something more sensible, which > partially defeats the point of this refactoring work I have been doing). > > > > I am not sure this behaviour is unique for just `NamedFieldPuns`, but my > question is: > > > > 1. What prevents us from adding `NamedFieldPuns` as a proper constructor for > the `Extension` type and in principle remove `RecordPuns`? Backward > compatibility I assume? > > > > > > Many thanks, > > > > Alfredo > > > > > > > > > > > > > > > > > > _______________________________________________ > ghc-devs mailing list > ghc-devs@haskell.org > http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs
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