Add a pattern-syn form of PromotionErr

The main change is to add PatSynPE to PromotionErr, so that
when we get an ill-staged use of a pattern synonym we get a
civilised error message.

We were already doing this in half-baked form in tcValBinds, but
this patch tidies up the impl (which previously used a hack rather
than APromotionErr), and does it in tcTyClsInstDecls too.

5 files changed, 21 insertions, 6 deletions

diff --git a/testsuite/tests/patsyn/should_fail/T11265.hs b/testsuite/tests/patsyn/should_fail/T11265.hs
new file mode 100644
index 0000000000..a7ee5c4fbf
--- /dev/null
+++ b/testsuite/tests/patsyn/should_fail/T11265.hs
@@ -0,0 +1,6 @@
+{-# LANGUAGE PatternSynonyms, DataKinds #-}
+
+pattern A = True
+
+class    F a
+instance F A
diff --git a/testsuite/tests/patsyn/should_fail/T11265.stderr b/testsuite/tests/patsyn/should_fail/T11265.stderr
new file mode 100644
index 0000000000..eda5d35a9d
--- /dev/null
+++ b/testsuite/tests/patsyn/should_fail/T11265.stderr
@@ -0,0 +1,6 @@
+
+T11265.hs:6:12: error:
+    • Pattern synonym ‘A’ cannot be used here
+        (Pattern synonyms cannot be promoted)
+    • In the first argument of ‘F’, namely ‘A’
+      In the instance declaration for ‘F A’
diff --git a/testsuite/tests/patsyn/should_fail/T9161-1.stderr b/testsuite/tests/patsyn/should_fail/T9161-1.stderr
index 4e744694e2..04d9b31bf7 100644
--- a/testsuite/tests/patsyn/should_fail/T9161-1.stderr
+++ b/testsuite/tests/patsyn/should_fail/T9161-1.stderr
@@ -1,5 +1,6 @@
-

-T9161-1.hs:6:14: error:

-    Pattern synonym ‘PATTERN’ used as a type

-    In the type signature:

-      wrongLift :: PATTERN

+
+T9161-1.hs:6:14: error:
+    • Pattern synonym ‘PATTERN’ cannot be used here
+        (Pattern synonyms cannot be promoted)
+    • In the type signature:
+        wrongLift :: PATTERN
diff --git a/testsuite/tests/patsyn/should_fail/T9161-2.stderr b/testsuite/tests/patsyn/should_fail/T9161-2.stderr
index b7a1f360d7..409b922776 100644
--- a/testsuite/tests/patsyn/should_fail/T9161-2.stderr
+++ b/testsuite/tests/patsyn/should_fail/T9161-2.stderr
@@ -1,6 +1,7 @@
 
 T9161-2.hs:8:20: error:
-    • Pattern synonym ‘PATTERN’ used as a type
+    • Pattern synonym ‘PATTERN’ cannot be used here
+        (Pattern synonyms cannot be promoted)
     • In the first argument of ‘Proxy’, namely ‘PATTERN’
       In the type signature:
         wrongLift :: Proxy PATTERN ()
diff --git a/testsuite/tests/patsyn/should_fail/all.T b/testsuite/tests/patsyn/should_fail/all.T
index 6ef64ae5ed..eeb405b316 100644
--- a/testsuite/tests/patsyn/should_fail/all.T
+++ b/testsuite/tests/patsyn/should_fail/all.T
@@ -27,3 +27,4 @@ test('export-type-synonym', normal, compile_fail, [''])
 test('export-ps-rec-sel', normal, compile_fail, [''])
 test('T11053', normal, compile, ['-fwarn-missing-pat-syn-sigs'])
 test('T10426', normal, compile_fail, [''])
+test('T11265', normal, compile_fail, [''])