Fix tweag#236: allow files in "data" attributes.

Also adds a test that the data file is passed transitively through runfiles.

haskell/haskell.bzl

@@ -60,6 +60,7 @@ _haskell_common_attrs = {
   ),
   "data": attr.label_list(
     doc = "See [Bazel documentation](https://docs.bazel.build/versions/master/be/common-definitions.html#common.data).",
+    allow_files = True,
     cfg = "data",
   ),
   "compiler_flags": attr.string_list(

tests/binary-with-data/BUILD

@@ -10,6 +10,8 @@ haskell_binary(
   main_file = "bin1.hs",
   prebuilt_dependencies = ["base"],
   visibility = ["//visibility:public"],
+  # Regular file input:
+  data = ["bin1-input"],
 )
 
 haskell_binary(

tests/binary-with-data/bin1-input

@@ -0,0 +1 @@
+contents

tests/binary-with-data/bin1.hs

@@ -1,3 +1,9 @@
 module Main where
 
-main = return ()
+import Control.Monad (unless)
+
+main :: IO ()
+main = do
+    contents <- readFile "tests/binary-with-data/bin1-input"
+    unless (contents == "contents\n")
+      $ error $ "Incorrect input; got " ++ show contents

tests/binary-with-data/bin3.cc

@@ -0,0 +1,3 @@
+int main() {
+  return 0;
+}