Solo instance heads are printed incorrectly

[treeowl]

The documentation of GHC.Generics shows the instance for Generic1 Solo, but not the instance for Generic (Solo a). The instance is definitely there; indeed, if you click through to the source, you'll see it derived.

[treeowl]

Interestingly, the documentation for that module also has a mysterious extra instance: instance Generic (a).

[treeowl]

Aha! These are connected! For some reason, Haddock displays fully-applied Solo in instances as parentheses. So instance Generic (Solo a) is displayed as Generic (a) even though a function f :: Solo a -> Solo a will have its type displayed correctly.

[phadej]

This is even "worse": Solo a is systematically printed as (a) e.g. in Solo instance list:

It might be the

haddock/haddock-api/src/Haddock/Backends/Xhtml/Decl.hs

Lines 1255 to 1256 in 4cf2f4d

	ppr_mono_ty (HsTupleTy _ con tys) u q _ =
	tupleParens con (map (ppLType u q HideEmptyContexts) tys)

(and similar place in PDF backend).

EDIT: I'd rename this issue to Solo instance heads are printed incorrectly

[treeowl]

@phadej, renamed. I missed your request.