[Haskell-cafe] Ambiguous occurence error, despite use of DuplicateRecordFields (worked with ghc 8.10.7, not with 9.6.4)

[Tom Ellis]

Hello Han,

Would it be possible to produce a minimal example that demonstrates
the problem?  Or at the very least share the code?  It's very hard to
know where to start diagnosing.  (Although perhaps someone else knows
without having to see code.)

At a wild guess, have you been hit by this?

> As of GHC 9.4.1, selector names have to be entirely unambiguous
> (under the usual name resolution rules), while for record updates,
> there must be at most one datatype that has all the field names
> being updated.

https://ghc.gitlab.haskell.org/ghc/doc/users_guide/exts/duplicate_record_fields.html#extension-DuplicateRecordFields

Tom



On Tue, Apr 09, 2024 at 12:18:14PM +0200, Han Joosten wrote:
> Hi all,
> 
> I am currently migrating a Haskell project that uses ghc 8.10.7 to ghc
> 9.6.4.
> 
> Using the new version, I get errors like
> 
> ~~~.haskell
> Ambiguous occurrence ‘pos’
> It could refer to
>    either the field ‘pos’ of record ‘PClassify’,
>           defined at
> /workspaces/AmpersandNamespace/src/Ampersand/Core/ParseTree.hs:1265:5
>        or the field ‘pos’ of record ‘PPurpose’,
>           defined at
> /workspaces/AmpersandNamespace/src/Ampersand/Core/ParseTree.hs:1186:5
>        or the field ‘pos’ of record ‘P_ViewSegment’,
>           defined at
> /workspaces/AmpersandNamespace/src/Ampersand/Core/ParseTree.hs:1129:5
>        or the field ‘pos’ of record ‘P_ViewD’,
>           defined at
> /workspaces/AmpersandNamespace/src/Ampersand/Core/ParseTree.hs:1080:5
>        or the field ‘pos’ of record ‘P_IdentDf’,
>           defined at
> /workspaces/AmpersandNamespace/src/Ampersand/Core/ParseTree.hs:1024:5
>        or the field ‘pos’ of record ‘P_BoxItem’,
>           defined at
> /workspaces/AmpersandNamespace/src/Ampersand/Core/ParseTree.hs:981:9
>        or the field ‘pos’ of record ‘TemplateKeyValue’,
>           defined at
> /workspaces/AmpersandNamespace/src/Ampersand/Core/ParseTree.hs:959:5
>        or the field ‘pos’ of record ‘BoxHeader’,
>           defined at
> /workspaces/AmpersandNamespace/src/Ampersand/Core/ParseTree.hs:947:5
>        or the field ‘pos’ of record ‘P_SubIfc’,
>           defined at
> /workspaces/AmpersandNamespace/src/Ampersand/Core/ParseTree.hs:934:9
>        or the field ‘pos’ of record ‘P_Interface’,
>           defined at
> /workspaces/AmpersandNamespace/src/Ampersand/Core/ParseTree.hs:899:5
>        or the field ‘pos’ of record ‘P_Population’,
>           defined at
> /workspaces/AmpersandNamespace/src/Ampersand/Core/ParseTree.hs:870:9
>        or the field ‘pos’ of record ‘P_Rule’,
>           defined at
> /workspaces/AmpersandNamespace/src/Ampersand/Core/ParseTree.hs:806:5
>        or the field ‘pos’ of record ‘PairViewSegment’,
>           defined at
> /workspaces/AmpersandNamespace/src/Ampersand/Core/ParseTree.hs:740:9
>        or the field ‘pos’ of record ‘P_NamedRel’,
>           defined at
> /workspaces/AmpersandNamespace/src/Ampersand/Core/ParseTree.hs:591:5
>        or the field ‘pos’ of record ‘PAtomPair’,
>           defined at
> /workspaces/AmpersandNamespace/src/Ampersand/Core/ParseTree.hs:467:5
>        or the field ‘pos’ of record ‘Pragma’,
>           defined at
> /workspaces/AmpersandNamespace/src/Ampersand/Core/ParseTree.hs:415:5
>        or the field ‘pos’ of record ‘P_Relation’,
>           defined at
> /workspaces/AmpersandNamespace/src/Ampersand/Core/ParseTree.hs:408:5
>        or the field ‘pos’ of record ‘Representation’,
>           defined at
> /workspaces/AmpersandNamespace/src/Ampersand/Core/ParseTree.hs:339:5
>        or the field ‘pos’ of record ‘PConceptDef’,
>           defined at
> /workspaces/AmpersandNamespace/src/Ampersand/Core/ParseTree.hs:268:5
>        or the field ‘pos’ of record ‘P_Pattern’,
>           defined at
> /workspaces/AmpersandNamespace/src/Ampersand/Core/ParseTree.hs:209:5
>        or the field ‘pos’ of record ‘Role’,
>           defined at
> /workspaces/AmpersandNamespace/src/Ampersand/Core/ParseTree.hs:185:5
>        or the field ‘pos’ of record ‘P_RoleRule’,
>           defined at
> /workspaces/AmpersandNamespace/src/Ampersand/Core/ParseTree.hs:172:5
>        or the field ‘pos’ of record ‘P_Enforce’,
>           defined at
> /workspaces/AmpersandNamespace/src/Ampersand/Core/ParseTree.hs:152:5
>        or the field ‘pos’ of record ‘MetaData’,
>           defined at
> /workspaces/AmpersandNamespace/src/Ampersand/Core/ParseTree.hs:136:5
> 
> Previously, it was totally fine to have different data types each have a
> field with the same name, as long as you used `DuplicateRecordFields`
> 
> I have searched the migration documentation but I couldn't find any clue on
> why this has been changed or how to deal with it. I probably missed it.
> Any help is mostly appreciated!
> 
> Thanks for reading
> Cheers,
> Han Joosten

> _______________________________________________
> Haskell-Cafe mailing list
> To (un)subscribe, modify options or view archives go to:
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> Only members subscribed via the mailman list are allowed to post.