GHCi should not defer typed holes

In the function `tcUserStmt` in compiler/typecheck/TcRnDriver.hs, before
going over the different ways ('plans') to lift an expression typed at
the prompt into the GHCi monad, `Opt_DeferTypeErrors` is disabled. Here is
the accompanying comment:

```
-- Ensure that type errors don't get deferred when type checking the
-- naked expression. Deferring type errors here is unhelpful because the
-- expression gets evaluated right away anyway. It also would potentially
-- emit redundant type-error warnings, one from each plan.
; plan <- unsetGOptM Opt_DeferTypeErrors $
```

Since `Opt_DeferTypeErrors` implies `Opt_DeferTypedHoles`,
`Opt_DeferTypedHoles` should be disabled here as well. This improves
the error message for T10248 (it doesn't mention ghciStepIO anymore).
This is a partial fix for #10249, and a complete fix for #11130.

Depends on D1526

Reviewers: simonpj, austin, bgamari

Reviewed By: simonpj

Subscribers: simonpj

Differential Revision: https://phabricator.haskell.org/D1527

GHC Trac Issues: #10249, #11130

1 files changed, 14 insertions, 16 deletions

diff --git a/testsuite/tests/ghci/scripts/T10248.stderr b/testsuite/tests/ghci/scripts/T10248.stderr
index 59b0b29078..86b8c8d688 100644
--- a/testsuite/tests/ghci/scripts/T10248.stderr
+++ b/testsuite/tests/ghci/scripts/T10248.stderr
@@ -1,16 +1,14 @@
-

-<interactive>:2:10: warning:

-    Found hole: _ :: IO ()

-    In the second argument of ‘(<$>)’, namely ‘_’

-    In the first argument of ‘ghciStepIO :: IO a -> IO a’, namely

-      ‘Just <$> _’

-    In a stmt of an interactive GHCi command:

-      it <- ghciStepIO :: IO a -> IO a (Just <$> _)

-*** Exception: <interactive>:2:10: error:

-    Found hole: _ :: IO ()

-    In the second argument of ‘(<$>)’, namely ‘_’

-    In the first argument of ‘ghciStepIO :: IO a -> IO a’, namely

-      ‘Just <$> _’

-    In a stmt of an interactive GHCi command:

-      it <- ghciStepIO :: IO a -> IO a (Just <$> _)

-(deferred type error)

+
+<interactive>:2:10: error:
+    Found hole: _ :: f a
+    Where: ‘f’ is a rigid type variable bound by
+               the inferred type of it :: Functor f => f (Maybe a)
+               at <interactive>:2:1
+           ‘a’ is a rigid type variable bound by
+               the inferred type of it :: Functor f => f (Maybe a)
+               at <interactive>:2:1
+    In the second argument of ‘(<$>)’, namely ‘_’
+    In the expression: Just <$> _
+    In an equation for ‘it’: it = Just <$> _
+    Relevant bindings include
+      it :: f (Maybe a) (bound at <interactive>:2:1)