Reject top-level typed TH splices. Fixes #10945

When TemplateHaskell language extension is enabled it is valid to have
top-level expressions.  Each such expression is treated as a contents
of a splice.  The problem arises with typed splices.  They are not valid
at the top level and therefore we should interpret them not as a splice
but as a top-level expression (aka. implicit splice).  So saying:

$$foo

is equivalent of:

$( $$foo )

This patch makes sure that this is indeed the case.  Until now we
incorrectly treated typed splices as explicit splices.

1 files changed, 11 insertions, 4 deletions

diff --git a/compiler/parser/RdrHsSyn.hs b/compiler/parser/RdrHsSyn.hs
index 8bc4f6c076..e64a57519d 100644
--- a/compiler/parser/RdrHsSyn.hs
+++ b/compiler/parser/RdrHsSyn.hs
@@ -263,11 +263,18 @@ mkSpliceDecl :: LHsExpr RdrName -> HsDecl RdrName
 -- but if she wrote, say,
 --      f x            then behave as if she'd written $(f x)
 --                     ie a SpliceD
+--
+-- Typed splices are not allowed at the top level, thus we do not represent them
+-- as spliced declaration.  See #10945
 mkSpliceDecl lexpr@(L loc expr)
-  | HsSpliceE splice <- expr = SpliceD (SpliceDecl (L loc splice) ExplicitSplice)
-  | otherwise                = SpliceD (SpliceDecl (L loc splice) ImplicitSplice)
-  where
-    splice = mkUntypedSplice lexpr
+  | HsSpliceE splice@(HsUntypedSplice {}) <- expr
+  = SpliceD (SpliceDecl (L loc splice) ExplicitSplice)
+
+  | HsSpliceE splice@(HsQuasiQuote {}) <- expr
+  = SpliceD (SpliceDecl (L loc splice) ExplicitSplice)
+
+  | otherwise
+  = SpliceD (SpliceDecl (L loc (mkUntypedSplice lexpr)) ImplicitSplice)
 
 mkRoleAnnotDecl :: SrcSpan
                 -> Located RdrName                   -- type being annotated