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

third_party/bazel/rules_haskell/tests/repl-flags/BUILD.bazel

@@ -0,0 +1,45 @@
+load("@io_tweag_rules_haskell//haskell:haskell.bzl", "haskell_test")
+
+package(default_testonly = 1)
+
+# This test the `compiler` flags in many ways:
+# - the test needs to be built with `-DTESTS_TOOLCHAIN_COMPILER_FLAGS`, provided by the toolchain attribute `compiler_flags`
+# - the test needs `-XOverloadedStrings`, provided by this rule `compiler_flags`
+# - toolchain and rule `compiler_flags` are additive, else one of the previous test will fail
+# - the ordering is as such as rule flags are more important that toolchain flags
+
+# This rule must build correctly (using `bazel build`), but also as a repl (using `bazel run //tests/repl-flags:compiler_flags@repl`)
+haskell_test(
+    name = "compiler_flags",
+    srcs = ["CompilerFlags.hs"],
+
+    # This also ensure that local `compiler_flags` does not override the `global ones`
+    compiler_flags = ["-XOverloadedStrings"],
+    visibility = ["//visibility:public"],
+    deps = [
+        "//tests/hackage:base",
+        "//tests/hackage:bytestring",
+    ],
+)
+
+# This test the `repl_ghci_args` flags in a similar way
+# - the test needs to be built with `-DTESTS_TOOLCHAIN_REPL_FLAGS`, provided by the toolchain attribute `compiler_flags`
+# - the test needs `-XOverloadedStrings`, provided by toolchain `repl_ghci_args`
+# - toolchain and rule `compiler_flags` are additive, else one of the previous test will fail
+# - the ordering is as such as rule flags are more important that
+#    toolchain flags and that repl flags are more important that
+#    copmiler flags
+
+# This rule must build correctly (using `bazel build`), but also as a repl (using `bazel run //tests/repl-flags:compiler_flags@repl`). The final result between the repl and the binary must be different
+haskell_test(
+    name = "repl_flags",
+    srcs = ["ReplFlags.hs"],
+
+    # This also ensure that local `repl_flags` does not override the `global ones`
+    repl_ghci_args = ["-DTESTS_TOOLCHAIN_REPL_FLAGS"],
+    visibility = ["//visibility:public"],
+    deps = [
+        "//tests/hackage:base",
+        "//tests/hackage:bytestring",
+    ],
+)

third_party/bazel/rules_haskell/tests/repl-flags/CompilerFlags.hs

@@ -0,0 +1,10 @@
+{-# LANGUAGE CPP #-}
+
+module Main where
+
+import Data.ByteString
+
+#ifdef TESTS_TOOLCHAIN_COMPILER_FLAGS
+main = print ("hello" :: ByteString)
+#endif
+

third_party/bazel/rules_haskell/tests/repl-flags/ReplFlags.hs

@@ -0,0 +1,17 @@
+{-# LANGUAGE CPP #-}
+module Main where
+
+import Data.ByteString
+
+-- Ensure that `compiler-flags` are correctly set
+#ifdef TESTS_TOOLCHAIN_COMPILER_FLAGS
+main = print "hello"
+#endif
+
+-- Ensure that `repl_ghci_args` are correctly set
+-- OverloadedString is passed by toolchain
+-- The CPP constant is unset by toolchain and set by rule, so ordering must be ensured
+#ifdef TESTS_TOOLCHAIN_REPL_FLAGS
+foo = ("world" :: ByteString)
+#endif
+