PartialTypeSignatures trigger bogus "unbound implicit parameter" error

GHC seems to forget about in-scope implicit parameters when there's a hole in the type signature. Given

{-# LANGUAGE ImplicitParams, PartialTypeSignatures #-}

module Bad where

f1 :: (?loc :: Int, _) => Int
f1 = ?loc

f2 :: (?loc :: Int) => _
f2 = ?loc

GHC incorrectly reports the following errors.

% ghc -fforce-recomp Bad.hs
[1 of 1] Compiling Bad              ( Bad.hs, Bad.o )

Bad.hs:8:6:
    Unbound implicit parameter (?loc::Int)
      arising from a use of implicit parameter ‘?loc’
    In the expression: ?loc
    In an equation for ‘f1’: f1 = ?loc

Bad.hs:11:1:
    Occurs check: cannot construct the infinite type:
      _ ~ (?loc::Int) => _
    When checking that ‘f2’ has the specified type
      f2 :: (?loc::Int) => _
    Probable cause: the inferred type is ambiguous

Bad.hs:11:6:
    Unbound implicit parameter (?loc::_)
      arising from a use of implicit parameter ‘?loc’
    Relevant bindings include f2 :: _ (bound at Bad.hs:11:1)
    In the expression: ?loc
    In an equation for ‘f2’: f2 = ?loc

?loc is very clearly bound by both f1 and f2's signature. f2 additionally reports what looks to me to be a bogus occurs-check error; we know from the theta that ?loc :: Int so the hole should be solved for Int.

I suspect this is all related to the fact that PartialTypeSignatures triggers tcPolyInfer instead of tcPolyCheck.

I think this is the same underlying bug as #10846 (closed).

Trac metadata

Trac field	Value
Version	7.10.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture