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

third_party/bazel/rules_haskell/tests/external-haskell-repository/BUILD.bazel

@@ -0,0 +1,17 @@
+# Tests correct linking of haskell packages that were created
+# in a different bazel repository, e.g. with hazel.
+
+load(
+    "@io_tweag_rules_haskell//haskell:haskell.bzl",
+    "haskell_test",
+)
+
+haskell_test(
+    name = "external-haskell-repository",
+    srcs = ["Main.hs"],
+    visibility = ["//visibility:public"],
+    deps = [
+        "//tests/hackage:base",
+        "@haskell_package_repository_dummy//:library-with-cbits",
+    ],
+)

third_party/bazel/rules_haskell/tests/external-haskell-repository/Main.hs

@@ -0,0 +1,6 @@
+module Main where
+
+import AddOne
+import Control.Exception (assert)
+
+main = assert (addOne 41 == 42) $ return ()

third_party/bazel/rules_haskell/tests/external-haskell-repository/workspace_dummy.bzl

@@ -0,0 +1,64 @@
+# This file constructs a dummy workspace to test
+# haskell binaries that are included from outside repositories
+# (because linking external repositories works differently).
+
+# Repo-ception, in the sense that we build a WORKSPACE
+# that references the workspaces already set up in the
+# `rules_haskell` WORKSPACE.
+def _haskell_package_repository_dummy_impl(rep_ctx):
+    rep_ctx.file(
+        "WORKSPACE",
+        executable = False,
+        content = """
+repository(name={name})
+
+register_toolchains(
+  "@io_tweag_rules_haskell//tests/:ghc"
+)
+""".format(name = rep_ctx.name),
+    )
+
+    # this mirrors tests/library-with-cbits
+
+    rep_ctx.file(
+        "BUILD",
+        executable = False,
+        content = """
+load(
+  "@io_tweag_rules_haskell//haskell:haskell.bzl",
+  "haskell_toolchain",
+  "haskell_library",
+)
+load(
+  "@io_tweag_rules_haskell//:constants.bzl",
+  "test_ghc_version",
+)
+
+haskell_library(
+  name = "library-with-cbits",
+  srcs = ["AddOne.hs"],
+  deps = [
+      "@io_tweag_rules_haskell//tests/data:ourclibrary",
+      "@io_tweag_rules_haskell//tests/hackage:base",
+  ],
+
+  linkstatic = False,
+  visibility = ["//visibility:public"],
+)
+""",
+    )
+
+    rep_ctx.file(
+        "AddOne.hs",
+        executable = False,
+        content = """
+module AddOne where
+
+foreign import ccall "c_add_one" addOne :: Int -> Int
+""",
+    )
+
+haskell_package_repository_dummy = repository_rule(
+    _haskell_package_repository_dummy_impl,
+    local = True,
+)