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

third_party/bazel/rules_haskell/haskell/private/java.bzl

@@ -0,0 +1,48 @@
+"""Interop with Java."""
+
+load("@bazel_skylib//lib:collections.bzl", "collections")
+
+JavaInteropInfo = provider(
+    doc = "Information needed for interop with Java rules.",
+    fields = {
+        "inputs": "Files needed during build.",
+        "env": "Dict with env variables that should be set during build.",
+    },
+)
+
+def java_interop_info(ctx):
+    """Gather information from any Java dependencies.
+
+    Args:
+      ctx: Rule context.
+
+    Returns:
+      JavaInteropInfo: Information needed for Java interop.
+    """
+
+    inputs = depset(
+        transitive = [
+            # We only expose direct dependencies, though we could
+            # expose transitive ones as well. Only exposing the direct
+            # ones corresponds to Bazel's "strict Java dependencies"
+            # mode. See
+            # https://github.com/tweag/rules_haskell/issues/96.
+            dep[JavaInfo].compile_jars
+            for dep in ctx.attr.deps
+            if JavaInfo in dep
+        ],
+    )
+
+    env_dict = dict()
+    uniq_classpath = collections.uniq([
+        f.path
+        for f in inputs
+    ])
+
+    if len(uniq_classpath) > 0:
+        env_dict["CLASSPATH"] = ":".join(uniq_classpath)
+
+    return JavaInteropInfo(
+        inputs = inputs,
+        env = env_dict,
+    )