Add TemplateHaskell support for Overlapping pragmas

Reviewers: hvr, goldfire, austin, RyanGlScott, bgamari

Reviewed By: RyanGlScott, bgamari

Subscribers: RyanGlScott, thomie

Differential Revision: https://phabricator.haskell.org/D2118

1 files changed, 29 insertions, 0 deletions

diff --git a/testsuite/tests/th/TH_overlaps.hs b/testsuite/tests/th/TH_overlaps.hs
new file mode 100644
index 0000000000..9fd2180dcb
--- /dev/null
+++ b/testsuite/tests/th/TH_overlaps.hs
@@ -0,0 +1,29 @@
+{-# LANGUAGE TemplateHaskell, FlexibleInstances #-}
+module TH_overlaps where
+
+import Language.Haskell.TH
+
+class C1 a where c1 :: a
+class C2 a where c2 :: a
+class C3 a where c3 :: a
+
+[d|
+  instance {-# OVERLAPPABLE #-} C1 [a]      where c1 = []
+  instance                      C1 [Int]    where c1 = [1]
+
+  instance                      C2 [a]      where c2 = []
+  instance {-# OVERLAPPING #-}  C2 [Int]    where c2 = [1]
+
+  instance                      C3 [a]      where c3 = []
+  instance {-# OVERLAPS #-}     C3 [[a]]    where c3 = [[]]
+  instance                      C3 [[Int]]  where c3 = [[1]]
+  |]
+
+test1 :: ([Char],[Int])
+test1 = (c1,c1)
+
+test2 :: ([Char],[Int])
+test2 = (c2,c2)
+
+test3 :: ([Char],[[Char]],[[Int]])
+test3 = (c3,c3,c3)