Clearer error msg for newtype GADTs with defaulted kind

When a newtype introduces GADT eq_specs due to a defaulted
RuntimeRep, we detect this and print the error message with
explicit kinds.

This also refactors newtype type checking to use the new
diagnostic infra.

Fixes #21447

14 files changed, 53 insertions, 34 deletions

diff --git a/testsuite/tests/gadt/T14719.stderr b/testsuite/tests/gadt/T14719.stderr
index cfac00c0c0..e71f0e78e5 100644
--- a/testsuite/tests/gadt/T14719.stderr
+++ b/testsuite/tests/gadt/T14719.stderr
@@ -8,9 +8,10 @@ T14719.hs:5:3: error:
 5 |   MkFoo1 :: Bool
   |   ^^^^^^^^^^^^^^
 
-T14719.hs:8:3: error:
-    • The constructor of a newtype must have exactly one field
+T14719.hs:8:3: error: [GHC-23517]
+    • A newtype constructor must have exactly one field
         but ‘MkFoo2’ has none
+      MkFoo2 :: Foo2
     • In the definition of data constructor ‘MkFoo2’
       In the newtype declaration for ‘Foo2’
   |
diff --git a/testsuite/tests/indexed-types/should_fail/T14033.stderr b/testsuite/tests/indexed-types/should_fail/T14033.stderr
index fbc6b54486..d302c6dfdc 100644
--- a/testsuite/tests/indexed-types/should_fail/T14033.stderr
+++ b/testsuite/tests/indexed-types/should_fail/T14033.stderr
@@ -1,6 +1,7 @@
 
-T14033.hs:5:16: error:
-    • The constructor of a newtype must have exactly one field
+T14033.hs:5:16: error: [GHC-23517]
+    • A newtype constructor must have exactly one field
         but ‘Zero’ has none
+      Zero :: Zero
     • In the definition of data constructor ‘Zero’
       In the newtype declaration for ‘Zero’
diff --git a/testsuite/tests/indexed-types/should_fail/T2334A.stderr b/testsuite/tests/indexed-types/should_fail/T2334A.stderr
index d4cd3285c2..75d33cd3eb 100644
--- a/testsuite/tests/indexed-types/should_fail/T2334A.stderr
+++ b/testsuite/tests/indexed-types/should_fail/T2334A.stderr
@@ -1,13 +1,14 @@
 
-T2334A.hs:9:26: error:
-    • The constructor of a newtype must have exactly one field
-        but ‘F’ has two
+T2334A.hs:9:26: error: [GHC-23517]
+    • A newtype constructor must have exactly one field but ‘F’ has two
+      F :: () -> () -> F ()
     • In the definition of data constructor ‘F’
       In the newtype instance declaration for ‘F’
 
-T2334A.hs:10:27: error:
-    • The constructor of a newtype must have exactly one field
+T2334A.hs:10:27: error: [GHC-23517]
+    • A newtype constructor must have exactly one field
         but ‘H’ has none
+      H :: F Int
     • In the definition of data constructor ‘H’
       In the newtype instance declaration for ‘F’
 
diff --git a/testsuite/tests/linear/should_fail/LinearGADTNewtype.stderr b/testsuite/tests/linear/should_fail/LinearGADTNewtype.stderr
index 42207d4f72..465476d603 100644
--- a/testsuite/tests/linear/should_fail/LinearGADTNewtype.stderr
+++ b/testsuite/tests/linear/should_fail/LinearGADTNewtype.stderr
@@ -1,5 +1,6 @@
 
-LinearGADTNewtype.hs:3:4: error:
+LinearGADTNewtype.hs:3:4: error: [GHC-38291]
     • A newtype constructor must be linear
+      A :: Int -> A
     • In the definition of data constructor ‘A’
       In the newtype declaration for ‘A’
diff --git a/testsuite/tests/parser/should_fail/readFail008.stderr b/testsuite/tests/parser/should_fail/readFail008.stderr
index 8fd289a301..e79a4ef8f2 100644
--- a/testsuite/tests/parser/should_fail/readFail008.stderr
+++ b/testsuite/tests/parser/should_fail/readFail008.stderr
@@ -1,6 +1,5 @@
 
-readFail008.hs:5:15:
-    A newtype constructor cannot have a strictness annotation,
-      but ‘T’ does
-    In the definition of data constructor ‘T’
-    In the newtype declaration for ‘N’
+readFail008.hs:5:15: error: [GHC-04049]
+    • A newtype constructor must not have a strictness annotation
+    • In the definition of data constructor ‘T’
+      In the newtype declaration for ‘N’
diff --git a/testsuite/tests/polykinds/T11459.stderr b/testsuite/tests/polykinds/T11459.stderr
index 724395ecd7..ae65ea5613 100644
--- a/testsuite/tests/polykinds/T11459.stderr
+++ b/testsuite/tests/polykinds/T11459.stderr
@@ -1,6 +1,6 @@
 
-T11459.hs:9:20: error:
-    • A newtype constructor cannot have existential type variables
+T11459.hs:9:20: error: [GHC-07525]
+    • A newtype constructor must not have existential type variables
       Parser :: forall a {k}.
                 (forall (f :: k -> *) (r :: k).
                  Failure f r -> Success a f r -> f r)
diff --git a/testsuite/tests/typecheck/should_fail/T15523.stderr b/testsuite/tests/typecheck/should_fail/T15523.stderr
index 83b7cdbc60..07133257c5 100644
--- a/testsuite/tests/typecheck/should_fail/T15523.stderr
+++ b/testsuite/tests/typecheck/should_fail/T15523.stderr
@@ -1,6 +1,7 @@
 
-T15523.hs:5:20: error:
-    • The constructor of a newtype must have exactly one field
+T15523.hs:5:20: error: [GHC-23517]
+    • A newtype constructor must have exactly one field
         but ‘Foo’ has none
+      Foo :: Duration
     • In the definition of data constructor ‘Foo’
       In the newtype declaration for ‘Duration’
diff --git a/testsuite/tests/typecheck/should_fail/T15796.stderr b/testsuite/tests/typecheck/should_fail/T15796.stderr
index 3aa7ae8d65..81cbc85b63 100644
--- a/testsuite/tests/typecheck/should_fail/T15796.stderr
+++ b/testsuite/tests/typecheck/should_fail/T15796.stderr
@@ -1,6 +1,6 @@
 
-T15796.hs:6:3: error:
-    • A newtype constructor cannot have a context in its type
+T15796.hs:6:3: error: [GHC-17440]
+    • A newtype constructor must not have a context in its type
       MkN :: forall a. Show a => a -> N a
     • In the definition of data constructor ‘MkN’
       In the newtype declaration for ‘N’
diff --git a/testsuite/tests/typecheck/should_fail/T17955.stderr b/testsuite/tests/typecheck/should_fail/T17955.stderr
index 0762facf45..3b5a5b2676 100644
--- a/testsuite/tests/typecheck/should_fail/T17955.stderr
+++ b/testsuite/tests/typecheck/should_fail/T17955.stderr
@@ -1,6 +1,6 @@
 
-T17955.hs:6:13: error:
-    • A newtype constructor cannot have a context in its type
+T17955.hs:6:13: error: [GHC-17440]
+    • A newtype constructor must not have a context in its type
       T :: Coercible () T => () -> T
     • In the definition of data constructor ‘T’
       In the newtype declaration for ‘T’
diff --git a/testsuite/tests/typecheck/should_fail/T18891a.stderr b/testsuite/tests/typecheck/should_fail/T18891a.stderr
index 881924c8a1..a1ef9607bf 100644
--- a/testsuite/tests/typecheck/should_fail/T18891a.stderr
+++ b/testsuite/tests/typecheck/should_fail/T18891a.stderr
@@ -1,12 +1,12 @@
 
-T18891a.hs:8:4: error:
-    • A newtype constructor must have a return type of form T a1 ... an
-      MkN1 :: N1 -> N1
+T18891a.hs:8:4: error: [GHC-89498]
+    • A newtype must not be a GADT
+      MkN1 :: N1 @GHC.Types.LiftedRep -> N1 @GHC.Types.LiftedRep
     • In the definition of data constructor ‘MkN1’
       In the newtype declaration for ‘N1’
 
-T18891a.hs:12:3: error:
-    • A newtype constructor must have a return type of form T a1 ... an
-      MkN2 :: N2 -> N2
+T18891a.hs:12:3: error: [GHC-89498]
+    • A newtype must not be a GADT
+      MkN2 :: N2 @GHC.Types.LiftedRep -> N2 @GHC.Types.LiftedRep
     • In the definition of data constructor ‘MkN2’
       In the newtype declaration for ‘N2’
diff --git a/testsuite/tests/typecheck/should_fail/T21447.hs b/testsuite/tests/typecheck/should_fail/T21447.hs
new file mode 100644
index 0000000000..7a6938d5ad
--- /dev/null
+++ b/testsuite/tests/typecheck/should_fail/T21447.hs
@@ -0,0 +1,8 @@
+module T21447 where
+
+import Data.Kind (Type)
+import GHC.Exts  (TYPE)
+
+type H :: TYPE r -> Type
+newtype H a where
+  H :: a -> H a
diff --git a/testsuite/tests/typecheck/should_fail/T21447.stderr b/testsuite/tests/typecheck/should_fail/T21447.stderr
new file mode 100644
index 0000000000..aeba975cba
--- /dev/null
+++ b/testsuite/tests/typecheck/should_fail/T21447.stderr
@@ -0,0 +1,6 @@
+
+T21447.hs:8:3: error: [GHC-89498]
+    • A newtype must not be a GADT
+      H :: forall a. a -> H @GHC.Types.LiftedRep a
+    • In the definition of data constructor ‘H’
+      In the newtype declaration for ‘H’
diff --git a/testsuite/tests/typecheck/should_fail/all.T b/testsuite/tests/typecheck/should_fail/all.T
index 51d73be7ed..efad13aacd 100644
--- a/testsuite/tests/typecheck/should_fail/all.T
+++ b/testsuite/tests/typecheck/should_fail/all.T
@@ -659,3 +659,4 @@ test('T21338', normal, compile_fail, [''])
 test('T21158', normal, compile_fail, [''])
 test('T21583', normal, compile_fail, [''])
 test('MissingDefaultMethodBinding', normal, compile_fail, [''])
+test('T21447', normal, compile_fail, [''])
diff --git a/testsuite/tests/typecheck/should_fail/tcfail156.stderr b/testsuite/tests/typecheck/should_fail/tcfail156.stderr
index 280f118f90..e50ebcbde4 100644
--- a/testsuite/tests/typecheck/should_fail/tcfail156.stderr
+++ b/testsuite/tests/typecheck/should_fail/tcfail156.stderr
@@ -1,6 +1,6 @@
 
-tcfail156.hs:7:15:
-    A newtype constructor cannot have existential type variables
-    Foo :: forall a. a -> Foo
-    In the definition of data constructor ‘Foo’
-    In the newtype declaration for ‘Foo’
+tcfail156.hs:7:15: error: [GHC-07525]
+    • A newtype constructor must not have existential type variables
+      Foo :: forall a. a -> Foo
+    • In the definition of data constructor ‘Foo’
+      In the newtype declaration for ‘Foo’