built failure

[phadej]

src/Graphics/SVGFonts/Text.hs:53:35: error:
    Ambiguous occurrence ‘Default’
    It could refer to
       either ‘Data.Default.Class.Default’,
              imported from ‘Data.Default.Class’ at src/Graphics/SVGFonts/Text.hs:34:1-25
           or ‘Diagrams.Prelude.Default’,
              imported from ‘Diagrams.Prelude’ at src/Graphics/SVGFonts/Text.hs:35:1-68
              (and originally defined in ‘data-default-0.8.0.0:Data.Default.Internal’)
   |
53 | instance (Read n, RealFloat n) => Default (TextOpts n) where

---

I think that recent revisions to diagrams ecosystem related to data-default-0.8 major breakage were handled too softly.

As Default is part of external interface, it's just created a mess.

Latest diagrams-lib uses data-default, but SVGFonts depends on data-default-class. Old data-default-class and new data-default can co-exist, which causes install plans like above having two different Default in scope possible.

---

IMHO the only clean solution is to have major releases of everything (withDefault in public API), and only use the later data-default. data-default change was big and disruptive, I don't see a way to go around it in non-major way.

[phadej]

But one can begin with by having

data-default-class (>=0.1 && <0.3)

revised to

data-default-class (>=0.2 && <0.3)

---

It still may cause problems to the end users, but at least it won't fail to compile itself.

[byorgey]

Thanks for reporting, I'll look into this soon!