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, 36 insertions, 0 deletions

diff --git a/testsuite/tests/backpack/should_compile/bkp61.bkp b/testsuite/tests/backpack/should_compile/bkp61.bkp
new file mode 100644
index 0000000000..3ad7d721bb
--- /dev/null
+++ b/testsuite/tests/backpack/should_compile/bkp61.bkp
@@ -0,0 +1,36 @@
+-- Check that we can implement abstract data using a data family.
+
+{-# LANGUAGE DataKinds #-}
+{-# LANGUAGE TypeFamilies #-}
+
+unit p where
+  signature H where
+    import Data.Kind
+    type T :: Bool -> Type
+    data T b
+    turnOff :: T True  -> T False
+    turnOn  :: T False -> T True
+  module A where
+    import H
+    foo :: T True -> T True
+    foo = turnOn . turnOff
+
+unit q where
+  module H where
+    import Data.Kind
+    type D :: Bool -> Type
+    data family D a
+    data instance D True  = DT
+    data instance D False = DF
+    turnOff DT = DF
+    turnOn  DF = DT
+
+    type S = D
+    type T = S
+
+unit r where
+  dependency q
+  dependency p[H=q:H]
+  module N where
+    import A
+    bar = foo . foo