Add tests for T17820

testsuite/tests/th/T17820a.hs

+{-# LANGUAGE TemplateHaskell #-}
+
+module Main where
+
+data D = C ()
+
+$( const mempty C )

testsuite/tests/th/T17820a.stderr

+
+T17820a.hs:7:17: error:
+    GHC stage restriction:
+      ‘C’ is used in a top-level splice, quasi-quote, or annotation,
+      and must be imported, not defined locally

testsuite/tests/th/T17820b.hs

+{-# LANGUAGE TemplateHaskell #-}
+
+module Main where
+
+data D = C { f :: () }
+
+$( const mempty f )

testsuite/tests/th/T17820b.stderr

+
+T17820b.hs:7:17: error:
+    GHC stage restriction:
+      ‘f’ is used in a top-level splice, quasi-quote, or annotation,
+      and must be imported, not defined locally

testsuite/tests/th/T17820c.hs

+{-# LANGUAGE TemplateHaskell #-}
+
+module Main where
+
+class C t where
+  meth :: t ()
+
+$( const mempty (meth :: forall t. C t => t ()) )

testsuite/tests/th/T17820c.stderr

+
+T17820c.hs:8:18: error:
+    GHC stage restriction:
+      ‘meth’ is used in a top-level splice, quasi-quote, or annotation,
+      and must be imported, not defined locally

testsuite/tests/th/T17820d.hs

+{-# LANGUAGE TemplateHaskell #-}
+
+module Main where
+
+decls = [d| data D = MkD { foo :: Int }
+            blargh = $(const [| 0 |] foo) |]

testsuite/tests/th/T17820d.stderr

+
+T17820d.hs:6:38: error:
+    • Stage error: ‘foo’ is bound at stage 2 but used at stage 1
+    • In the untyped splice: $(const [| 0 |] foo)
+      In the Template Haskell quotation
+        [d| data D = MkD {foo :: Int}
+            blargh = $(const [| 0 |] foo) |]

testsuite/tests/th/T17820e.hs

+{-# LANGUAGE TemplateHaskell, TypeFamilies #-}
+
+module Main where
+
+data family F a
+
+data instance F () = C ()
+
+$( const mempty C )

testsuite/tests/th/T17820e.stderr

+
+T17820e.hs:9:17: error:
+    GHC stage restriction:
+      ‘C’ is used in a top-level splice, quasi-quote, or annotation,
+      and must be imported, not defined locally

testsuite/tests/th/all.T

@@ -534,3 +534,8 @@ test('T19737', normal, compile, [''])
 test('T19759', normal, compile, [''])
 test('T20060', normal, compile, [''])
 test('T20179', normal, compile_fail, [''])
+test('T17820a', normal, compile_fail, [''])
+test('T17820b', normal, compile_fail, [''])
+test('T17820c', normal, compile_fail, [''])
+test('T17820d', normal, compile_fail, [''])
+test('T17820e', normal, compile_fail, [''])