Add show @printer support for polymorphic variants
#286
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gasche
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Jun 1, 2024
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Thanks! This is a nice thing to have, and the implementation in this PR is slightly better than #267. Let's not make it wait as long...
Could you maybe include a CHANGELOG entry to credit both you and @ghuysmans, so that we don't forget to do so later?
| @@ -23,6 +23,7 @@ let attr_printer context = Attribute.declare "deriving.show.printer" context | |||
| Ast_pattern.(single_expr_payload __) (fun e -> e) | |||
| let ct_attr_printer = attr_printer Attribute.Context.core_type | |||
| let constr_attr_printer = attr_printer Attribute.Context.constructor_declaration | |||
| let rtag_attr_printer = attr_printer Attribute.Context.rtag | |||
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I was lost for a while as to what rtag means. The answer is that this obscure name comes from the parsetree, and it means "a constructor declaration in a polymorphic variant type" (r means row and tag is supposed to suggest constructor, I guess). The other PR #267 uses attr_printer field.prf_attributes directly, and I suppose that usig the ppxlib mechanism as in here is better.
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This missing support is listed as one of the motivations for ppx_deriving_variant_string:
I quickly implemented this and only then discovered that #267 already exists.
The difference is that this is for the migrated ppxlib attributes and does use
wrap_printer.