-Wmissing-signatures should warn when top-level signature is partial

I'd like GHC to emit a warning for the following definition:

g :: _
g = True

But not for that one:

f :: Int
f = x
  where
    x :: _
    x = 1

The context is that I'm using partial signatures to help the type checker give the right type to a binding, with no intention of filling the holes later. (what Richard calls elision here)

The warning accompanying partial signatures (-Wpartial-type-signatures) effectively treats _-s in type signatures as holes which are meant to be filled (the type-level equivalent of typed holes). Which is not useful to my usage.

I can deactivate -Wpartial-type-signatures, however, it seems to me that, in that case, a partial top-level signature is just as bad as a missing top-level signature. So it seems to me that whenever I have -Wmissing-signatures enabled I also want to warn for partial top-level signatures.

Trac metadata

Trac field	Value
Version	8.6.3
Type	FeatureRequest
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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CC	goldfire, simonpj
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