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> 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> *On Behalf Of *Alfredo Di > Napoli > *Sent:* 06 July 2021 10:14 > *To:* Simon Peyton Jones via ghc-devs <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
