feat(third_party/bazel): Check in rules_haskell from Tweag

third_party/bazel/rules_haskell/tests/java_classpath/BUILD.bazel

@@ -0,0 +1,17 @@
+load(
+    "@io_tweag_rules_haskell//haskell:haskell.bzl",
+    "haskell_test",
+)
+
+package(default_testonly = 1)
+
+haskell_test(
+    name = "java_classpath",
+    srcs = ["Main.hs"],
+    visibility = ["//visibility:public"],
+    deps = [
+        "//tests/hackage:base",
+        "//tests/hackage:template-haskell",
+        "@org_apache_spark_spark_core_2_10//jar",
+    ],
+)

third_party/bazel/rules_haskell/tests/java_classpath/Main.hs

@@ -0,0 +1,17 @@
+{-# LANGUAGE LambdaCase      #-}
+{-# LANGUAGE TemplateHaskell #-}
+module Main (main) where
+
+import qualified Language.Haskell.TH as TH (runIO)
+import qualified Language.Haskell.TH.Syntax as TH (lift)
+import           System.Environment (lookupEnv)
+
+main :: IO ()
+main = putStrLn $(
+  let ensureClassPath :: IO String
+      ensureClassPath = lookupEnv "CLASSPATH" >>= \case
+        Nothing -> error "CLASSPATH not set when it was expected to be."
+        Just "" -> error "CLASSPATH empty when it was expected to have content."
+        Just cpath -> pure $ "java-classpath at compile time: " ++ cpath
+  in TH.runIO ensureClassPath >>= TH.lift
+  )