Enable CI tests

.bazelci/presubmit.yml

@@ -1,14 +1,41 @@
 ---
+build_targets: &build_targets
+  - "//..."
+  # TODO: Look into broken targets in //toolchains
+  - "-//toolchains/..."
+
+build_targets_bzlmod: &build_targets_bzlmod
+  - "//..."
+  - "-//toolchains/..."
+  # TODO(pcloudy): pkg_tar doesn't work with Bzlmod due to https://github.com/bazelbuild/bazel/issues/14259
+  # Enable once the issue is fixed.
+  - "-//distro/..."
+
 buildifier:
   version: latest
   warnings: "all"
 tasks:
   ubuntu2004:
-    build_targets:
-    - "//..."
+    build_targets: *build_targets
   macos:
-    build_targets:
-    - "//..."
+    build_targets: *build_targets
   windows:
-    build_targets:
-    - "//..."
+    build_targets: *build_targets
+  ubuntu2004_bzlmod:
+    bazel: last_green
+    platform: ubuntu2004
+    build_flags:
+      - "--config=bzlmod"
+    build_targets: *build_targets_bzlmod
+  macos_bzlmod:
+    bazel: last_green
+    platform: macos
+    build_flags:
+      - "--config=bzlmod"
+    build_targets: *build_targets_bzlmod
+  windows_bzlmod:
+    bazel: last_green
+    platform: windows
+    build_flags:
+      - "--config=bzlmod"
+    build_targets: *build_targets_bzlmod

.bazelrc

@@ -0,0 +1,6 @@
+build:bzlmod --experimental_enable_bzlmod
+# @local_config_cc and @local_config_xcode are no longer available as canonical repo name,
+# therefore we have to override the default value of the following flags.
+# TODO: Figure out a way to get rid of this.
+build:bzlmod --crosstool_top=@rules_cc.0.0.1.cc_configure.local_config_cc//:toolchain
+build:bzlmod --xcode_version_config=@rules_cc.0.0.1.cc_configure.local_config_xcode//:host_xcodes

examples/hello-world/BUILD

@@ -0,0 +1,7 @@
+load("//java:defs.bzl", "java_binary")
+
+java_binary(
+    name = "hello-world",
+    srcs = ["HelloWorld.java"],
+    main_class = "HelloWorld",
+)

examples/hello-world/HelloWorld.java

@@ -0,0 +1,19 @@
+// Copyright 2021 The Bazel Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+public class HelloWorld {
+  public static void main (String[] args) {
+    System.out.println("Hello World!");
+  }
+}