Commit 4212674b authored by Simon Peyton Jones's avatar Simon Peyton Jones Committed by Ben Gamari
Browse files

Fix inference of partial signatures

When we had
  f :: ( _ ) => blah
we were failing to call growThetaTyVars, as we do in the
no-type-signature case, and that meant that we weren't generalising
over the right type variables.  I'm quite surprised this didn't cause
problems earlier.

Anyway Trac #12844 showed it up and this patch fixes it

(cherry picked from commit 1bfff60f)
parent 80c26da8
......@@ -778,8 +778,11 @@ chooseInferredQuantifiers inferred_theta tau_tvs qtvs
| PartialSig { sig_cts = extra } <- bndr_info
, Just loc <- extra
= do { annotated_theta <- zonkTcTypes annotated_theta
; let free_tvs = closeOverKinds (tyCoVarsOfTypes annotated_theta
`unionVarSet` tau_tvs)
; let free_tvs = closeOverKinds (growThetaTyVars inferred_theta seed_tvs)
-- growThetaVars just like the no-type-sig case
-- Omitting this caused #12844
seed_tvs = tyCoVarsOfTypes annotated_theta -- These are put there
`unionVarSet` tau_tvs -- by the user
my_theta = pickQuantifiablePreds free_tvs annotated_theta inferred_theta
-- Report the inferred constraints for an extra-constraints wildcard/hole as
......
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE PartialTypeSignatures #-}
{-# LANGUAGE PolyKinds #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE TypeOperators #-}
module T12844 where
barWraper :: ('(r,r') ~ Head rngs, Foo rngs) => FooData rngs
barWraper = bar
bar :: (_) => FooData rngs
bar = foo
data FooData rngs
class Foo xs where foo :: (Head xs ~ '(r,r')) => FooData xs
type family Head (xs :: [k]) where Head (x ': xs) = x
T12844.hs:12:9: warning: [-Wpartial-type-signatures (in -Wdefault)]
Found constraint wildcard ‘_’ standing for ‘(Head rngs ~ '(r, r'),
Foo rngs)’
In the type signature:
bar :: _ => FooData rngs
......@@ -64,3 +64,4 @@ test('T11016', normal, compile, [''])
test('T11192', normal, compile, [''])
test('T12156', normal, compile_fail, ['-fdefer-typed-holes'])
test('T12531', normal, compile, ['-fdefer-typed-holes'])
test('T12844', normal, compile, [''])
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