Suggest FFI extensions as hints (#20116)

- Use extension suggestion hints instead of suggesting extensions in the
error message body for several FFI errors.
- Adds a test case for `TcRnForeignImportPrimExtNotSet`

6 files changed, 26 insertions, 10 deletions

diff --git a/compiler/GHC/Tc/Errors/Ppr.hs b/compiler/GHC/Tc/Errors/Ppr.hs
index 6cdfe963c7..29da277c8d 100644
--- a/compiler/GHC/Tc/Errors/Ppr.hs
+++ b/compiler/GHC/Tc/Errors/Ppr.hs
@@ -48,7 +48,6 @@ import {-# SOURCE #-} GHC.Tc.Types (getLclEnvLoc)
 import GHC.Tc.Types.Origin
 import GHC.Tc.Types.Rank (Rank(..))
 import GHC.Tc.Utils.TcType
-import GHC.Types.Basic (UnboxedTupleOrSum(..), unboxedTupleOrSumExtension)
 import GHC.Types.Error
 import GHC.Types.FieldLabel (flIsOverloaded)
 import GHC.Types.Hint.Ppr () -- Outputable GhcHint
@@ -715,7 +714,7 @@ instance Diagnostic TcRnMessage where
 
     TcRnForeignImportPrimExtNotSet _decl
       -> mkSimpleDecorated $
-           text "Use GHCForeignImportPrim to allow `foreign import prim'."
+           text "`foreign import prim' requires GHCForeignImportPrim."
 
     TcRnForeignImportPrimSafeAnn _decl
       -> mkSimpleDecorated $
@@ -771,7 +770,7 @@ instance Diagnostic TcRnMessage where
                     text "because the data constructor for"
                     <+> quotes (ppr tc) <+> text "is not in scope"
                 UnliftedFFITypesNeeded ->
-                  innerMsg $$ text "To marshal unlifted types, use UnliftedFFITypes"
+                  innerMsg $$ text "UnliftedFFITypes is required to marshal unlifted types"
                 NotABoxedMarshalableTyCon -> innerMsg
                 ForeignLabelNotAPtr ->
                   innerMsg $$ text "A foreign-imported address (via &foo) must have type (Ptr a) or (FunPtr a)"
@@ -1298,7 +1297,7 @@ instance Diagnostic TcRnMessage where
     TcRnWarnDefaulting {}
       -> noHints
     TcRnForeignImportPrimExtNotSet{}
-      -> noHints
+      -> [suggestExtension LangExt.GHCForeignImportPrim]
     TcRnForeignImportPrimSafeAnn{}
       -> noHints
     TcRnForeignFunctionImportAsValue{}
@@ -1313,6 +1312,7 @@ instance Diagnostic TcRnMessage where
       -> case reason of
            TypeCannotBeMarshaled _ why
              | NewtypeDataConNotInScope{} <- why -> [SuggestImportingDataCon]
+             | UnliftedFFITypesNeeded <- why -> [suggestExtension LangExt.UnliftedFFITypes]
            _ -> noHints
     TcRnInvalidCIdentifier{}
       -> noHints
diff --git a/compiler/GHC/Tc/Errors/Types.hs b/compiler/GHC/Tc/Errors/Types.hs
index 7a44ab08ef..78be225cf9 100644
--- a/compiler/GHC/Tc/Errors/Types.hs
+++ b/compiler/GHC/Tc/Errors/Types.hs
@@ -1701,7 +1701,7 @@ data TcRnMessage where
      Example(s):
      foreign import prim "foo" foo :: ByteArray# -> (# Int#, Int# #)
 
-    Test cases: None
+    Test cases: ffi/should_fail/T20116
   -}
   TcRnForeignImportPrimExtNotSet :: ForeignImport -> TcRnMessage
 
diff --git a/testsuite/tests/ffi/should_fail/T10461.stderr b/testsuite/tests/ffi/should_fail/T10461.stderr
index 3421467715..47df47b97f 100644
--- a/testsuite/tests/ffi/should_fail/T10461.stderr
+++ b/testsuite/tests/ffi/should_fail/T10461.stderr
@@ -1,7 +1,8 @@
 
 T10461.hs:6:1: error:
-    Unacceptable result type in foreign declaration:
-      ‘Word#’ cannot be marshalled in a foreign call
-      To marshal unlifted types, use UnliftedFFITypes
-    When checking declaration:
-      foreign import prim safe cheneycopy :: Any -> Word#
+    • Unacceptable result type in foreign declaration:
+        ‘Word#’ cannot be marshalled in a foreign call
+        UnliftedFFITypes is required to marshal unlifted types
+    • When checking declaration:
+        foreign import prim safe cheneycopy :: Any -> Word#
+    Suggested fix: Perhaps you intended to use UnliftedFFITypes
diff --git a/testsuite/tests/ffi/should_fail/T20116.hs b/testsuite/tests/ffi/should_fail/T20116.hs
new file mode 100644
index 0000000000..ca8c4fbbdf
--- /dev/null
+++ b/testsuite/tests/ffi/should_fail/T20116.hs
@@ -0,0 +1,8 @@
+{-# LANGUAGE MagicHash #-}
+{-# LANGUAGE ForeignFunctionInterface #-}
+
+module Foo where
+
+import GHC.Exts
+
+foreign import prim "test_lt" lt_s :: Int64# -> Int64# -> Int#
diff --git a/testsuite/tests/ffi/should_fail/T20116.stderr b/testsuite/tests/ffi/should_fail/T20116.stderr
new file mode 100644
index 0000000000..dbc06bf9a0
--- /dev/null
+++ b/testsuite/tests/ffi/should_fail/T20116.stderr
@@ -0,0 +1,6 @@
+
+T20116.hs:8:1: error:
+    • `foreign import prim' requires GHCForeignImportPrim.
+    • When checking declaration:
+        foreign import prim safe "test_lt" lt_s :: Int64# -> Int64# -> Int#
+    Suggested fix: Perhaps you intended to use GHCForeignImportPrim
diff --git a/testsuite/tests/ffi/should_fail/all.T b/testsuite/tests/ffi/should_fail/all.T
index ce1c10534e..24210dcca6 100644
--- a/testsuite/tests/ffi/should_fail/all.T
+++ b/testsuite/tests/ffi/should_fail/all.T
@@ -16,6 +16,7 @@ test('T7506', normal, compile_fail, [''])
 test('T7243', normal, compile_fail, [''])
 test('T10461', normal, compile_fail, [''])
 test('T16702', normal, compile_fail, [''])
+test('T20116', normal, compile_fail, [''])
 
 # UnsafeReenter tests implementation of an undefined behavior (calling Haskell
 # from an unsafe foreign function) and only makes sense in non-threaded way