Add regression test for #12926

Closes #12926

2 files changed, 37 insertions, 0 deletions

diff --git a/testsuite/tests/typecheck/should_compile/T12926.hs b/testsuite/tests/typecheck/should_compile/T12926.hs
new file mode 100644
index 0000000000..a642e67053
--- /dev/null
+++ b/testsuite/tests/typecheck/should_compile/T12926.hs
@@ -0,0 +1,36 @@
+{-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE MultiParamTypeClasses #-}
+
+module A where
+
+import GHC.Base
+import qualified Data.Vector.Unboxed.Base
+import qualified Data.Vector.Generic.Base
+import Data.Vector.Generic.Mutable
+import qualified Data.Vector.Generic.Mutable.Base
+import Data.Vector.Generic (fromList)
+
+data A = A Int Int Int
+
+instance Data.Vector.Unboxed.Base.Unbox A
+
+newtype instance Data.Vector.Unboxed.Base.MVector s_a4iX A
+  = MV_A (Data.Vector.Unboxed.Base.MVector s_a4iX (Int, Int, Int))
+
+instance MVector Data.Vector.Unboxed.Base.MVector A where
+  basicLength (MV_A v) =
+    basicLength v
+  basicUnsafeSlice idx len (MV_A v) =
+    MV_A (basicUnsafeSlice idx len v)
+  basicUnsafeNew len =
+    MV_A `liftM` (basicUnsafeNew len)
+  basicUnsafeWrite (MV_A v) idx val_a4iW =
+    basicUnsafeWrite v idx ((\ (A a_a4iT b_a4iU c_a4iV) -> (a_a4iT, b_a4iU, c_a4iV)) val_a4iW)
+
+newtype instance Data.Vector.Unboxed.Base.Vector A =
+  V_A (Data.Vector.Unboxed.Base.Vector (Int, Int, Int))
+
+instance Data.Vector.Generic.Base.Vector Data.Vector.Unboxed.Base.Vector A where
+
+mkA :: Data.Vector.Unboxed.Base.Vector A
+mkA = fromList []
diff --git a/testsuite/tests/typecheck/should_compile/all.T b/testsuite/tests/typecheck/should_compile/all.T
index e80a82fc98..d143251f9b 100644
--- a/testsuite/tests/typecheck/should_compile/all.T
+++ b/testsuite/tests/typecheck/should_compile/all.T
@@ -696,3 +696,4 @@ test('T17343', exit_code(1), compile_and_run, [''])
 test('T17566', [extra_files(['T17566a.hs'])], makefile_test, [])
 test('T12760', unless(compiler_debugged(), skip), compile, ['-O'])
 test('T13142', normal, compile, ['-O2'])
+test('T12926', reqlib('vector'), compile, ['-O2'])