Migrate errors to diagnostics in GHC.Tc.Module

This commit migrates the errors in GHC.Tc.Module to use the new
diagnostic infrastructure.

It required a significant overhaul of the compatibility checks between
an hs-boot or signature module and its implementation; we now use
a Writer monad to accumulate errors; see the BootMismatch datatype
in GHC.Tc.Errors.Types, with its panoply of subtypes.
For the sake of readability, several local functions inside the
'checkBootTyCon' function were split off into top-level functions.

We split off GHC.Types.HscSource into a "boot or sig" vs "normal hs file"
datatype, as this mirrors the logic in several other places where we
want to treat hs-boot and hsig files in a similar fashion.

This commit also refactors the Backpack checks for type synonyms
implementing abstract data, to correctly reject implementations that
contain qualified or quantified types (this fixes #23342 and #23344).

1 files changed, 47 insertions, 0 deletions

diff --git a/testsuite/tests/backpack/should_fail/bkpfail54.bkp b/testsuite/tests/backpack/should_fail/bkpfail54.bkp
new file mode 100644
index 0000000000..4248390c91
--- /dev/null
+++ b/testsuite/tests/backpack/should_fail/bkpfail54.bkp
@@ -0,0 +1,47 @@
+
+-- Check that we do something sensible when we implement
+-- abstract data with a quantified type.
+
+{-# LANGUAGE StandaloneKindSignatures #-}
+{-# LANGUAGE TypeFamilies #-}
+
+unit p where
+  module M where
+    import Data.Kind ( Type, Constraint )
+
+    type C :: Type -> Constraint
+    class C a where
+      type family F a :: Type
+
+unit q where
+  dependency p
+  signature H where
+    data T1
+    data T2
+    data T3
+  module N where
+    import M ( C(F) )
+    import H ( T1, T2, T3 )
+
+    instance C T1 where
+      type F T1 = T2
+    instance C T2 where
+      type F T2 = T3
+    instance C T3 where
+      type F T3 = T1
+
+unit r where
+  dependency p
+  module H where
+
+    class C2 a where {}
+    data S = MkS
+
+    type T1 = forall a. a -> a
+    type T2 = forall a. C2 a => a
+    type T3 = C2 S => S -> S
+
+unit s where
+  dependency p
+  dependency r
+  dependency q[H=r:H]