Fix printing of promoted MkSolo datacon (#22785)

Problem: In 2463df2f, the Solo data constructor was renamed to MkSolo,
and Solo was turned into a pattern synonym for backwards compatibility.
Since pattern synonyms can not be promoted, the old code that pretty-printed
promoted single-element tuples started producing ill-typed code:
   t :: Proxy ('Solo Int)
This fails with "Pattern synonym ‘Solo’ used as a type"

The solution is to track the distinction between type constructors and data
constructors more carefully when printing single-element tuples.

6 files changed, 25 insertions, 9 deletions

diff --git a/testsuite/tests/printer/T22785.hs b/testsuite/tests/printer/T22785.hs
new file mode 100644
index 0000000000..1db6b7d88d
--- /dev/null
+++ b/testsuite/tests/printer/T22785.hs
@@ -0,0 +1,8 @@
+{-# LANGUAGE DataKinds #-}
+module T22785 where
+import Data.Proxy
+import Data.Tuple
+
+
+p :: Proxy ('MkSolo Int)
+p = Proxy :: Proxy Int
diff --git a/testsuite/tests/printer/T22785.stderr b/testsuite/tests/printer/T22785.stderr
new file mode 100644
index 0000000000..05bf7bfb3d
--- /dev/null
+++ b/testsuite/tests/printer/T22785.stderr
@@ -0,0 +1,7 @@
+
+T22785.hs:8:5: [GHC-83865]
+     Couldn't match type ‘Int’ with ‘MkSolo Int’
+      Expected: Proxy (MkSolo Int)
+        Actual: Proxy Int
+     In the expression: Proxy :: Proxy Int
+      In an equation for ‘p’: p = Proxy :: Proxy Int
diff --git a/testsuite/tests/printer/all.T b/testsuite/tests/printer/all.T
index 409c9f2b13..cc4e4b3324 100644
--- a/testsuite/tests/printer/all.T
+++ b/testsuite/tests/printer/all.T
@@ -187,4 +187,5 @@ test('T22488_docHead', normal, compile_and_run, ['-package ghc'])
 test('T20531', extra_files(['T20531_defs.hs']), ghci_script, ['T20531.script'])
 test('T20531_red_ticks', extra_files(['T20531_defs.hs']), ghci_script, ['T20531_red_ticks.script'])
 test('HsDocTy', [ignore_stderr, req_ppr_deps], makefile_test, ['HsDocTy'])
-test('Test22765', [ignore_stderr, req_ppr_deps], makefile_test, ['Test22765'])
\ No newline at end of file
+test('Test22765', [ignore_stderr, req_ppr_deps], makefile_test, ['Test22765'])
+test('T22785', normal, compile_fail, [''])
diff --git a/testsuite/tests/th/T17380.stderr b/testsuite/tests/th/T17380.stderr
index d1f4684062..b5e79ffb63 100644
--- a/testsuite/tests/th/T17380.stderr
+++ b/testsuite/tests/th/T17380.stderr
@@ -25,17 +25,17 @@ T17380.hs:18:7: error: [GHC-83865]
 
 T17380.hs:21:8: error: [GHC-83865]
     • Couldn't match type: Maybe String
-                     with: 'Solo (Maybe String)
-      Expected: Proxy ('Solo (Maybe String))
+                     with: MkSolo (Maybe String)
+      Expected: Proxy (MkSolo (Maybe String))
         Actual: Proxy (Maybe String)
     • In the expression: Proxy :: Proxy (Maybe String)
       In an equation for ‘quuz’: quuz = Proxy :: Proxy (Maybe String)
 
 T17380.hs:24:8: error: [GHC-83865]
-    • Couldn't match type: 'Solo (Maybe String)
+    • Couldn't match type: MkSolo (Maybe String)
                      with: Maybe String
       Expected: Proxy (Maybe String)
-        Actual: Proxy ('Solo (Maybe String))
-    • In the expression: Proxy :: Proxy ('Solo Maybe String)
+        Actual: Proxy (MkSolo (Maybe String))
+    • In the expression: Proxy :: Proxy ('MkSolo Maybe String)
       In an equation for ‘fred’:
-          fred = Proxy :: Proxy ('Solo Maybe String)
+          fred = Proxy :: Proxy ('MkSolo Maybe String)
diff --git a/testsuite/tests/th/T18612.stderr b/testsuite/tests/th/T18612.stderr
index 0865ddc17b..b710dc3b39 100644
--- a/testsuite/tests/th/T18612.stderr
+++ b/testsuite/tests/th/T18612.stderr
@@ -1,7 +1,7 @@
 T18612.hs:14:11-68: Splicing type
     conT ''Proxy `appT` (promotedTupleT 1 `appT` (tupleT 0))
   ======>
-    Proxy ('Solo ())
+    Proxy ('MkSolo ())
 T18612.hs:(10,7)-(11,75): Splicing type
     arrowT `appT` (conT ''Identity `appT` (tupleT 1 `appT` (tupleT 0)))
       `appT` (conT ''Identity `appT` (tupleT 1 `appT` (tupleT 0)))
diff --git a/testsuite/tests/th/TH_Promoted1Tuple.stderr b/testsuite/tests/th/TH_Promoted1Tuple.stderr
index bd71507e2e..2453cb26d5 100644
--- a/testsuite/tests/th/TH_Promoted1Tuple.stderr
+++ b/testsuite/tests/th/TH_Promoted1Tuple.stderr
@@ -1,3 +1,3 @@
 
 TH_Promoted1Tuple.hs:7:2: error:
-    Illegal type: ‘'Solo Int’ Perhaps you intended to use DataKinds
+    Illegal type: ‘'MkSolo Int’ Perhaps you intended to use DataKinds