Test Trac #10248

testsuite/tests/ghci/scripts/T10248.script

+:set -fdefer-type-errors
+Just <$> _

testsuite/tests/ghci/scripts/T10248.stderr

+
+<interactive>:3:10: warning:
+    Found hole ‘_’ with type: IO ()
+    In the second argument of ‘(<$>)’, namely ‘_’
+    In the first argument of ‘ghciStepIO ::
+                                IO a_alT -> IO a_alT’, namely
+      ‘Just <$> _’
+    In a stmt of an interactive GHCi command:
+      it <- ghciStepIO :: IO a_alT -> IO a_alT (Just <$> _)
+*** Exception: <interactive>:3:10: error:
+    Found hole ‘_’ with type: IO ()
+    In the second argument of ‘(<$>)’, namely ‘_’
+    In the first argument of ‘ghciStepIO ::
+                                IO a_alT -> IO a_alT’, namely
+      ‘Just <$> _’
+    In a stmt of an interactive GHCi command:
+      it <- ghciStepIO :: IO a_alT -> IO a_alT (Just <$> _)
+(deferred type error)

testsuite/tests/ghci/scripts/all.T

@@ -216,3 +216,4 @@ test('T10408A', normal, run_command,
     ['$MAKE -s --no-print-directory T10408A'])
 test('T10408B', normal, run_command,
     ['$MAKE -s --no-print-directory T10408B'])
+test('T10248', normal, ghci_script, ['T10248.script'])