update to current master againwip/T13904

1 files changed, 69 insertions, 0 deletions

diff --git a/testsuite/tests/quantified-constraints/T15244.hs b/testsuite/tests/quantified-constraints/T15244.hs
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index 0000000000..16d2b65d53
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+++ b/testsuite/tests/quantified-constraints/T15244.hs
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+{-# LANGUAGE QuantifiedConstraints, TypeFamilies #-}
+
+module T15244 where
+class (forall t . Eq (c t)) => Blah c
+
+-- Unquantified works
+foo :: (Eq (a t), Eq (b t), a ~ b) => a t -> b t -> Bool
+foo a b = a == b
+-- Works
+
+-- Two quantified instances fail with double ambiguity check errors
+bar :: (forall t . Eq (a t), forall t . Eq (b t), a ~ b) => a t -> b t -> Bool
+bar a b = a == b
+-- Minimal.hs:11:8: error:
+--     • Could not deduce (Eq (b t1))
+--       from the context: (forall t1. Eq (a t1), forall t1. Eq (b t1),
+--                          a ~ b)
+--         bound by the type signature for:
+--                    bar :: forall (a :: * -> *) (b :: * -> *) t.
+--                           (forall t1. Eq (a t1), forall t1. Eq (b t1), a ~ b) =>
+--                           a t -> b t -> Bool
+--         at Minimal.hs:11:8-78
+--     • In the ambiguity check for ‘bar’
+--       To defer the ambiguity check to use sites, enable AllowAmbiguousTypes
+--       In the type signature:
+--         bar :: (forall t. Eq (a t), forall t. Eq (b t), a ~ b) =>
+--                a t -> b t -> Bool
+--    |
+-- 11 | bar :: (forall t . Eq (a t), forall t . Eq (b t), a ~ b) => a t -> b t -> Bool
+--    |
+-- [And then another copy of the same error]
+
+-- Two copies from superclass instances fail
+baz :: (Blah a, Blah b, a ~ b) => a t -> b t -> Bool
+baz a b = a == b
+-- Minimal.hs:34:11: error:
+--     • Could not deduce (Eq (b t)) arising from a use of ‘==’
+--       from the context: (Blah a, Blah b, a ~ b)
+--         bound by the type signature for:
+--                    baz :: forall (a :: * -> *) (b :: * -> *) t.
+--                           (Blah a, Blah b, a ~ b) =>
+--                           a t -> b t -> Bool
+--         at Minimal.hs:33:1-52
+--     • In the expression: a == b
+--       In an equation for ‘baz’: baz a b = a == b
+--    |
+-- 34 | baz a b = a == b
+--    |
+
+-- Two copies from superclass from same declaration also fail
+mugga :: (Blah a, Blah a) => a t -> a t -> Bool
+mugga a b = a == b
+--     • Could not deduce (Eq (a t)) arising from a use of ‘==’
+--       from the context: (Blah a, Blah a)
+--         bound by the type signature for:
+--                    mugga :: forall (a :: * -> *) t.
+--                             (Blah a, Blah a) =>
+--                             a t -> a t -> Bool
+--         at Minimal.hs:50:1-47
+--     • In the expression: a == b
+--       In an equation for ‘mugga’: mugga a b = a == b
+--    |
+-- 51 | mugga a b = a == b
+--    |
+
+-- One copy works
+quux :: (Blah a, a ~ b) => a t -> b t -> Bool
+quux a b = a == b
+-- Works