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, 9 insertions, 9 deletions

diff --git a/testsuite/tests/typecheck/should_fail/T20588.stderr b/testsuite/tests/typecheck/should_fail/T20588.stderr
index b9b7ed3f38..50e7bbec77 100644
--- a/testsuite/tests/typecheck/should_fail/T20588.stderr
+++ b/testsuite/tests/typecheck/should_fail/T20588.stderr
@@ -1,29 +1,29 @@
 
-T20588.hs-boot:8:1: error:
+T20588.hs-boot:8:1: error: [GHC-15843]
     Class ‘C’ has conflicting definitions in the module
-    and its hs-boot file
+    and its hs-boot file.
     Main module: type C :: * -> Constraint
                  class C a where
                    meth :: a -> a
                    {-# MINIMAL meth #-}
-    Boot file:   type C :: * -> Constraint
+      Boot file: type C :: * -> Constraint
                  class C a where
                    meth :: a -> a
                    {-# MINIMAL meth #-}
-    The methods do not match:
-      The default methods associated with ‘meth’ are different
+    The class methods do not match:
+      The default methods associated with ‘meth’ are different.
 
-T20588.hs-boot:11:1: error:
+T20588.hs-boot:11:1: error: [GHC-15843]
     Class ‘D’ has conflicting definitions in the module
-    and its hs-boot file
+    and its hs-boot file.
     Main module: type D :: * -> Constraint
                  class D a where
                    type T :: * -> *
                    type family T a
                      Default: Int
-    Boot file:   type D :: * -> Constraint
+      Boot file: type D :: * -> Constraint
                  class D a where
                    type T :: * -> *
                    type family T a
     The associated types do not match:
-      The associated type defaults differ
+      The types of the second associated type default differ.