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

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

@@ -0,0 +1,94 @@
+"""Package list handling"""
+
+load(":private/set.bzl", "set")
+
+def pkg_info_to_compile_flags(pkg_info, for_plugin = False):
+    """Map package info to GHC command-line arguments.
+
+    Args:
+      pkg_info: Package info collected by `ghc_info()`.
+      for_plugin: Whether the package is a plugin dependency.
+
+    Returns:
+      The list of command-line arguments that should be passed to GHC.
+    """
+    namespace = "plugin-" if for_plugin else ""
+    args = [
+        # In compile.bzl, we pass this just before all -package-id
+        # arguments. Not doing so leads to bizarre compile-time failures.
+        # It turns out that equally, not doing so leads to bizarre
+        # link-time failures. See
+        # https://github.com/tweag/rules_haskell/issues/395.
+        "-hide-all-{}packages".format(namespace),
+    ]
+
+    if not pkg_info.has_version:
+        args.extend([
+            # Macro version are disabled for all packages by default
+            # and enabled for package with version
+            # see https://github.com/tweag/rules_haskell/issues/414
+            "-fno-version-macros",
+        ])
+
+    for package in pkg_info.packages:
+        args.extend(["-{}package".format(namespace), package])
+
+    for package_id in pkg_info.package_ids:
+        args.extend(["-{}package-id".format(namespace), package_id])
+
+    for package_db in pkg_info.package_dbs:
+        args.extend(["-package-db", package_db])
+
+    return args
+
+def expose_packages(hs_info, lib_info, use_direct, use_my_pkg_id, custom_package_databases, version):
+    """
+    Returns the information that is needed by GHC in order to enable haskell
+    packages.
+
+    hs_info: is common to all builds
+    version: if the rule contains a version, we will export the CPP version macro
+
+    All the other arguments are not understood well:
+
+    lib_info: only used for repl and linter
+    use_direct: only used for repl and linter
+    use_my_pkg_id: only used for one specific task in compile.bzl
+    custom_package_databases: override the package_databases of hs_info, used only by the repl
+    """
+    has_version = version != None and version != ""
+
+    # Expose all prebuilt dependencies
+    #
+    # We have to remember to specify all (transitive) wired-in
+    # dependencies or we can't find objects for linking
+    #
+    # Set use_direct if hs_info does not have a direct_prebuilt_deps field.
+    packages = []
+    for prebuilt_dep in set.to_list(hs_info.direct_prebuilt_deps if use_direct else hs_info.prebuilt_dependencies):
+        packages.append(prebuilt_dep.package)
+
+    # Expose all bazel dependencies
+    package_ids = []
+    for package in set.to_list(hs_info.package_ids):
+        # XXX: repl and lint uses this lib_info flags
+        # It is set to None in all other usage of this function
+        # TODO: find the meaning of this flag
+        if lib_info == None or package != lib_info.package_id:
+            # XXX: use_my_pkg_id is not None only in compile.bzl
+            if (use_my_pkg_id == None) or package != use_my_pkg_id:
+                package_ids.append(package)
+
+    # Only include package DBs for deps, prebuilt deps should be found
+    # auto-magically by GHC
+    package_dbs = []
+    for cache in set.to_list(hs_info.package_databases if not custom_package_databases else custom_package_databases):
+        package_dbs.append(cache.dirname)
+
+    ghc_info = struct(
+        has_version = has_version,
+        packages = packages,
+        package_ids = package_ids,
+        package_dbs = package_dbs,
+    )
+    return ghc_info